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1. (WO2005060620) CATALYSEURS ET MATERIAUX D'ACCUMULATION D'HYDROGENE DEMONTRANT DES EFFETS QUANTIQUES
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CATALYSTS AND HYDROGEN STORAGE MATERIALS
EXHIBITING QUANTUM EFFECTS

FIELD OF INVENTION
This invention pertains to catalysts comprised of atomic aggregations having length scales in the quantum regime and to supported catalytic materials exhibiting quantum mechanical interactions. More particularly, this invention relates to catalysts having catalytic sites whose catalytic properties result from quantum mechanically induced modifications of electron density originating from wavefunction overlap of atoms comprising the catalytic material or between the catalytic material and the support. Most particularly, this invention relates to hydrogen storage materials having hydrogen storage sites with binding energies for atomic hydrogen that provide high hydrogen storage densities as well as favorable hydrogen release rates at temperatures only modestly above room temperature and to customization of catalytic function through the engineering of wavefunction overlap between metal particles and a surrounding support matrix.
BACKGROUND OF THE INVENTION
Hydrogen has been identified as a readily available fuel source with desirable combustion properties that can reduce the need for fossil fuels. The realization of a hydrogen based fuel economy requires the development of an infrastructure for making hydrogen accessible to the public. A key element of this infrastructure is a safe and reliable means for storing and delivering hydrogen. The storage of hydrogen in the solid state is the preferred method for storing hydrogen because it avoids the high pressures required for gas phase storage of hydrogen and the low temperatures required for liquid phase storage of hydrogen. The solid state storage of hydrogen is most effectively realized through hydrogen storage alloy materials. A hydrogen storage alloy is a solid state material that is capable of reversibly storing hydrogen, typically in the form of atomic hydrogen.
A conventional hydrogen storage alloy is a metal or metal alloy that includes catalytic sites and hydrogen storage sites. Storage of hydrogen is accomplished through the conversion of hydrogen gas to atomic hydrogen at catalytic sties followed by the binding or retention of hydrogen at hydrogen storage sites. In the hydrogen storage process, a hydrogen storage alloy is exposed to hydrogen gas, which adsorbs onto, diffuses into or otherwise interacts with the hydrogen storage alloy to reach the catalytic sites that convert it to atomic hydrogen. The atomic hydrogen subsequently migrates to a hydrogen storage site, where it is stably retained until the release process is initiated. The release of hydrogen is accomplished by adding thermal energy to the hydrogen storage alloy to free atomic hydrogen from hydrogen storage sites and induce migration of atomic hydrogen to catalytic sites that subsequently effect recombination of atomic hydrogen to form hydrogen gas, which then desorbs, diffuses or otherwise vacates the alloy to provide hydrogen fuel.
An important objective in hydrogen storage is the development of hydrogen storage alloys that are capable of storing large amounts of hydrogen in small volumes with rapid uptake and release of hydrogen. The realization of high hydrogen storage density and rapid kinetics for the storage and release processes requires careful consideration of the chemical and physical factors that contribute to the mechanisms that underlie the hydrogen storage and release processes. The kinetics of the hydrogen storage and release processes are promoted through the presence of a high number of catalytic sites having sufficient activity in a hydrogen storage alloy as well as through the existence of a sufficiently porous surrounding structural matrix to support the catalytic sites. A porous support matrix is desirable because it facilitates access of hydrogen gas to and from the catalytic sites during storage and release, respectively. A porous support matrix is also desirable because it promotes migration of atomic hydrogen to and from hydrogen storage sites during storage and release, respectively.
High hydrogen storage density is promoted through the presence of a high number of hydrogen storage sites that provide sufficient stabilizing interactions to bind or otherwise retain atomic hydrogen. Strong stabilizing interactions, however, precariously compete with the requirements for rapid release kinetics and release at reasonable temperatures. Although the strong binding of hydrogen is conducive to high hydrogen storage density, strongly bound hydrogen is difficult to liberate and is therefore detrimental to the objective of achieving rapid release kinetics. Strongly bound hydrogen can be released at reasonable rates only at high, and oftentimes inconvenient or impractical, temperatures.

Conventional hydrogen storage alloys are metals or metal alloys. The low porosity, high hydrogen binding energy and low concentration of catalytic sites limits the range of application of conventional hydrogen storage alloys. Since conventional hydrogen storage alloys present a trade-off between the two principal desired characteristics (high hydrogen storage density and rapid kinetics), products and applications of hydrogen storage materials have typically focused on optimizing one of the principle characteristics at the expense of the other. Current hydrogen storage alloys are incapable of providing the high hydrogen storage densities and rapid kinetics at reasonable temperatures required for a wide range of practical applications, including storage and delivery of hydrogen as a fuel for automobiles and other vehicles. The needs of this and other applications requires the development of new hydrogen storage materials based on new and non-conventional chemical and physical paradigms.
In addition to storage and retrieval of hydrogen, it is further necessary to find efficient ways to produce hydrogen from raw materials or chemical feedstocks. This goal implicates chemical reactions generally and specifically concerns rates of chemical reactions because the rate of a chemical reaction typically controls whether a particular reaction is practical or not. Much of the effort in the development of chemical reactions is directed toward the goal of increasing the reaction rate. The most common strategy for increasing the rate of a reaction is through the use of a catalyst.
An important class of existing catalytic materials is the so-called supported catalyst. A supported catalyst consists of a dispersed catalytic phase that is mechanically stabilized on an inert support matrix. The dispersed catalytic phase is typically a metal in the form of small particles (e.g. platinum or nickel) and the support is typically a metal oxide such as alumina or silica. Supported catalysts are highly effective because the dispersed catalytic phase has a high surface area and the catalytic particles are supported independently in a relatively unaggregated state. Although supported catalysts have for many reactions have been discovered, suitable catalysts for many reactions have yet to be discovered and many of the discovered catalysts are only partially effective. In order to extend the range of practical chemical reactions, it is necessary to identify new supported catalytic materials.

SUMMARY OF THE INVENTION
This invention provides a new class of catalytic and hydrogen storage materials that include chemical bonding and atomic arrangements that deviate from the atomic configurations found in conventional hydrogen storage alloys to provide new degrees of freedom in controlling hydrogen storage density and the kinetics of hydrogen storage and retrieval. The instant materials exploit beneficial properties that arise as the dimensions of the structural units of a catalytic or hydrogen storage material transcend the macroscopic length scales of conventional materials and enter the quantum regime. In the quantum limit, atomic arrangements become possible in which bond angles, bond lengths, coordination number and composition deviate from the prescribed conformity of the macroscopic limit. As a result, it becomes possible to control the distribution of electron density throughout the instant hydrogen storage materials and to thereby control the binding strength of hydrogen within the instant hydrogen storage materials. Catalytic activity is also beneficially affected in the quantum limit.
The instant catalytic or hydrogen storage materials comprise metals or metal alloys in angstrom scale atomic configurations. The bond angles and bond lengths within the configurations deviate from those of conventional materials. Enhanced catalytic activity and a broader spectrum of hydrogen binding energies is achieved by managing the intermolecular interactions responsible for chemical reactivity and binding through control of the local electron density within the instant catalytic or hydrogen storage materials. Bond angle deviations influence electron density by influencing wavefunction or orbital overlap and the degree of electron delocalization. Bond length deviations can also influence wavefunction or orbital overlap as well as the volume of space occupied by bonding electrons. Through the creation of materials in the quantum limit of dimensionality, the instant inventors have greatly expanded the range of atomic configurations available to metal atoms, thereby providing unprecedented control over the competing electronic interactions that govern catalytic performance in general, including the hydrogen storage and retrieval processes in hydrogen storage materials. Representative quantum limit materials according to the instant invention include Mg, Fe, Co, and V as well as alloys of these elements with each other and other elements in a supported or unsupported form. In supported embodiments, a catalytic phase is formed on, dispersed on or otherwise chemically or physically attached to a substrate or support matrix. In the quantum limit, interactions originating from wavefunction overlap develop between the catalytic phase and support matrix to provide modifications in electron density at catalytic sites and in portions of the support matrix in the vicinity of supported catalytic particles. These modifications constitute a quantum induced electronic interaction that enhances catalytic performance.
In one embodiment, the instant quantum limit materials are formed in an ultrasonic process. In this embodiment, one or more organometalUc precursor compounds is dissolved or suspended in a liquid and subjected to ultrasound. The ultrasound provides local heating and acoustic cavitation that lead to a concentration of energy in the vicinity of the precursor compounds. The energy concentration induces bond cleavage within molecules of the precursor compounds and prompts a reconfiguration of metal atoms or fragments liberated from molecular precursors to form the instant quantum limit materials.

In another embodiment, the instant quantum limit materials are formed in a thermal decomposition process. In this embodiment, one or more organometalUc precursor compounds is subjected to a heating treatment that induces thermal cleavage of bonds within molecules of the precursor compounds and a reorganization of metal atoms or fragments to form the instant quantum limit materials.
In yet another embodiment, the instant quantum limit materials are formed in a reductive chemical process. In this embodiment, one or more inorganic salts of one or more metals are combined in solution and subjected to chemical action through a strong reducing species. The reducing species reduces one or more metals from an oxidized state to a neutral state and promotes the formation of metallic clusters or aggregations having dimensions and atomic configurations in the quantum regime. The instant invention further presents a new concept in the design of supported catalysts.
Heretofore the catalytic function of supported catalysts has been provided by catalytic particles, typically metals, that are attached to a support matrix that is chemically inert and whose role is limited to one of providing mechanical support. The instant invention provides supported catalytic materials in which the support matrix interacts electronically with supported catalytic particles to influence the catalytic properties thereof to provide materials having new catalytic functionality. The electronic interaction between the support and the catalytic particles originates from the overlap of the wavefunctions of electrons associated with the catalytic particles and the support matrix. The wavefunction overlap provides a degree of freedom that may be used to modulate, alter or otherwise modify electron density at or near the surface of the catalytic particles to thereby influence the catalytic performance thereof. Representative materials according to the instant invention include catalytic metal or metal alloy particles supported on a metalUc or oxide support matrix.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1. PCT measurements of four samples of a hydrogen storage alloy. One sample was a control sample and three samples were mechanical alloys of the control sample with a quantum limit catalyst according to the instant invention.
Fig. 2. Hydrogen absorption characteristics of a Mg catalyst according to the instant invention at 30 °C,

50 °C, and l50 °C.
Fig. 3. Hydrogen absorption kinetics of a Mg catalyst according to the instant invention at 250 °C.

Fig. 4. Hydrogen absorption kinetics of a Mg catalyst according to the instant invention at 300 °C. Fig. 5A-5C. Schematic depictions of a catalytic phase supported by a support matrix.
DETAILED DESCRIPTION OF THE INVENTION
The instant invention provides quantum limit metals and metal alloys that provide superior catalytic and hydrogen storage properties. Catalysis (as well as chemical reactivity in general) and the energetics of binding and releasing adsorbed or absorbed species within a material ultimately depend on a balance of competing and oftentimes opposing steric and/or electronic interactions. Catalysis is a process that typically involves the binding of one or more reactant molecules to a catalytic site of a compound or material followed by reaction or rearrangement of the reactant species to form one or more product species, hi addition to providing a binding site, an important role of the catalytic site is a mediation of the electron density in the vicinity of the bound species. Depending on the reaction, catalysis typically involves an ability of a catalytic site to donate or withdraw electron density at the site of catalytic activity. This abiUty is required because the transformation of a reactant species to a product species inevitably involves a redistribution of electron density as some bonds break, other bonds form or the structure of a reactant species is rearranged. In a pure gas or liquid phase reaction, reactant molecules can to some extent accommodate a need to redistribute electron density through structurally distorted, transient intermediate states. At the surface of a solid state catalyst or in the coordination shell of a gas or liquid phase catalyst, however, the degrees of freedom of structural motion of a reactant species are limited and the ability of a catalyst to receive or donate electron density assumes increasing importance.
A hydrogen storage material is an example of a catalytic material. In a typical hydrogen storage material, hydrogen gas adsorbs onto the surface and becomes bound to a catalytic site at or near the surface. At the catalytic site, hydrogen gas is dissociated into hydrogen atoms that subsequently migrate or diffuse away from the catalytic site to a storage site. Since the number of surface sites is low, high hydrogen storage density requires efficient diffusion or migration of atomic hydrogen to storage sites in the interior of a hydrogen storage material. Atomic hydrogen becomes bound to the storage sites until energy is provided to initiate a release process. In the release process, atomic hydrogen departs storage sites, migrates or diffuses to a catalytic site where recombination of atomic hydrogen to form molecular hydrogen occurs. The molecular hydrogen so formed, subsequently departs the material and becomes available as hydrogen gas.
Electronic interactions, dictated by the distribution of electron density within a hydrogen storage material, influence the important processes associated with the storage and retrieval of hydrogen. The affected processes include: die binding of hydrogen gas to catalytic sites, the catalytic dissociation of molecular hydrogen, the diffusion or migration of atomic hydrogen to and from storage sites, the binding energy of atomic hydrogen in storage sites, and the catalytic association of atomic hydrogen to form molecular hydrogen.
From an applications standpoint, Uydrogen storage materials are required that show high hydrogen storage density and rapid hydrogen release at convenient operating temperatures. These two requirements, however, impose conflicting demands on the properties of a hydrogen storage material because high hydrogen storage density is promoted through storage sites having high binding energies, while rapid release of hydrogen from storage sites is promoted through low binding energies at desired operating temperatures. The design of hydrogen storage materials has thus represented a compromise between two competing influences.
An important class of conventional hydrogen storage materials is metals or metal alloys prepared, for example, by melting metalUc starting materials followed by subsequent cooling from the melt state. These materials include catalytic sites and storage sites where the storage sites have a distribution of binding energies. Many conventional metals and metal alloys exhibit high hydrogen storage densities (e.g. Mg and Mg-based alloys) due to high binding energies, but are limited in practice to operation at high temperatures (typically 150 °C and above) due to the slow hydrogen release kinetics that result from the need for stored hydrogen to overcome a high energy barrier to become liberated from a storage site. The high energy barrier is a consequence of the high binding energy associated with the hydrogen storage sites of conventional hydrogen storage materials. The predominant storage sites within the distribution of storage binding energies of conventional hydrogen storage materials have sufficiently high binding energies that appreciable hydrogen release rates occur only at higher operating temperatures.
In order to achieve acceptable hydrogen release rates at more convenient temperatures
(temperatures closer to room temperature), it is necessary to identify hydrogen storage materials that include a greater number of storage sites having binding energies conducive to rapid hydrogen release at temperatures below those of conventional hydrogen storage materials. In practice, this requires discovering new materials or modifying existing materials to provide a high concentration of hydrogen storage sites having binding energies that are lower than the binding energies of the predominant storage sites of conventional materials. In principle, lower binding energy sites can be produced through the creation of new types of storage sites or a shifting of the distribution of binding energies of existing materials to lower energy.
The binding energy of particular storage sites and the number of storage sites having a particular binding energy ultimately depend on the distribution of electron density within a hydrogen storage material, which, in turn, ultimately depends on the underlying structure and arrangement of atoms within a hydrogen storage material. The key to optimizing the properties of hydrogen storage materials Ues in achieving new degrees of freedom in controlling the structure and atomic configurations of hydrogen storage materials (or regions therein). Similar considerations apply to the optimization of the selectivity, efficiency, stabiUty and kinetics of catalytic materials generally where the structure, atomic configuration, and electron density (magnitude and spatial distribution thereof) within the material are essential to catalytic performance.
One of the instant inventors, S.R. Ovshinsky, has made numerous seminal contributions to fundamental and appUed chemistry and physics with a particular emphasis on the intelligent design of advanced chemical, electrical and optical materials with new and/or expanded functionality. A key concept advanced by Ovshinsky is an understanding of the new and varied degrees of freedom afforded by the disordered and amorphous states of matter. Ovshinsky recognized that the ordered crystalline lattice imposed many constraints on the structure and properties of materials due to a rigid adherence of atoms to a prescribed structural lattice and instead embraced the disordered and amorphous states for the enormous flexibility in chemical bonding, intermolecular interactions and structural configurations that they provide. Ovshinsky viewed disordered and amorphous materials in terms of constituent local structures, each of which has unique properties according to the chemical elements and topology present, which collectively and synergistically interact to produce macroscopic materials having macroscopic structures and properties that ultimately depend on the local compositions and orbital interactions of the constituent local structures.
Representative examples of the application of the Ovshinsky principles of materials design may be found, for example, in U.S. Pat. Nos. 4,177,473; 4,520,039; 4,664,960; 5,536,591; 5,616,432;
5,840,440 and 6,270,719 to the instant assignee, the disclosures of which are hereby incorporated by reference.
The instant hydrogen storage materials are aimed at controlling the binding strength of hydrogen in hydrogen storage alloys and at resolving the seeming conflict between simultaneously achieving high hydrogen storage capacity and fast hydrogen release kinetics at reasonable temperatures. In the instant invention, the Ovshinsky principles are further extended to address the need for achieving hydrogen storage materials having storage binding energies favorable to operation at temperatures below those of current materials. Although the Ovshinsky principles have been successfully applied to the enhancement in the activity and number of catalytic sites in hydrogen storage materials, the best hydrogen storage aUoys currently available still include hydrogen storage sites that are reminiscent of those that occur in conventional hydrogen storage alloys. More specifically, the hydrogen storage sites of the current hydrogen storage alloys are comprised of extended assemblies of metal atoms that are in close proximity to each other and that experience strong mutual electronic interactions. The binding strength of hydrogen to the storage sites of existing hydrogen storage alloys are accordingly high and as a result, commensurately high temperatures are needed to realize release of hydrogen at reasonable rates for practical appUcations, as described hereinabove.
Previous implementations of the Ovshinsky principles to the hydrogen storage sites have demonstrated the beneficial effects associated with creating hydrogen storage sites based on disordered assemblies of metal atoms. Disorder permits the creation and assemblage of local structures having unique topologies and electronic interactions and provides hydrogen storage materials that possess a broader spectrum of hydrogen storage sites than equilibrium Uydrogen storage alloys. The broader spectrum of sites includes non-conventional sites not found in equilibrium hydrogen storage alloys that are capable of binding hydrogen (see, for example U.S. Pat. No. 5,840,440).
In the instant hydrogen storage materials, the spectrum of hydrogen storage sites is enlarged to obtain storage sites displaying a wider range of binding strengths for hydrogen storage. Whereas previous work by Ovshinsky has emphasized the formation of a large number of storage sites, the instant invention emphasizes the formation of storage sites having a broader ranger of binding strengths. More specifically, the instant invention demonstrates the creation of hydrogen storage sites having reduced binding strengths relative to storage sites found in the currently available hydrogen storage materials. The binding strengths of the new storage sites are sufficiently high to effectively bind hydrogen, but not so high as to significantly inhibit discharge kinetics at temperatures only sUghtly above room temperature. As a result, the new class of hydrogen storage materials provides both high hydrogen storage capacity and rapid discharge kinetics at reasonable temperatures.
The instant inventors have recognized that the range of binding energies of storage sites in conventional hydrogen storage materials is necessarily limited because the structures of conventional hydrogen storage materials are rigidly prescribed by the constraints imposed by macroscopic length scales. In the instant invention, the inventors reaUze the release of these constraints through the formation of hydrogen storage materials having atomic configurations characterized by length scales in the quantum regime. The quantum regime is a non-macroscopic regime that offers new possibilities for structure and bonding within and between atomic aggregations. As a result, the quantum limit provides new opportunities for controlling tUe distribution of electron density within atomic aggregations and consequently, provides new opportunities for realizing hydrogen storage sites having unconventional binding energies better suited for hydrogen release at lower temperatures. Further rationale for working in the quantum limit is presented in the following discussion.
Motivation for the instant quantum limit materials originates from a consideration of the nature of the interaction of atomic hydrogen with hydrogen storage sites. The hydrogen storage process requires a localized stabilization of atomic hydrogen. This stabiUzation may be pbysical or cUemical in nature and is determined by a balance of intermolecular forces existing between tbe environment of a Uydrogen storage site and atomic Uydrogen. The stabilization may include covalent bond formation, ionic bond formation, dative bond formation, electrostatic interactions, or intermolecular interactions such as van der Waals interactions. The nature of the stabiUzing interaction influences the binding strength of hydrogen to a hydrogen storage site. Materials that stabilize hydrogen through direct bond formation generally have high binding strengths, whereas materials that stabilize hydrogen electrostatically generally have lower binding strengths.
Electron density at the hydrogen storage site is a fundamental property that underlies tUe binding strengtb of atomic Uydrogen. Hydrogen storage sites tUat exhibit high electron density tend to bind atomic hydrogen strongly and exhibit high heats of formation. In a Umiting case, sufficient electron density is available to permit formation of a metal-hydrogen bond at a single metal atom of the hydrogen storage alloy. While this limiting case may lead to high hydrogen storage density if sufficient sites are available, it also leads to strong binding of hydrogen, difficulties in liberating hydrogen during discharge and a requirement for high discharge temperatures. As the available electron density decreases, it becomes more difficult and ultimately impossible to form a direct metal-hydrogen bond and as a result, the binding strength of atomic hydrogen decreases and the heat of formation is reduced. At electron densities below those needed for formation of a direct metal-hydrogen bond, stabilization of atomic Uydrogen typically occurs over two or more metal atoms wUere each of the two or more atoms has insufficient electron density to stabiUze atomic hydrogen independently, but sufficient electron density to stabilize atomic Uydrogen in combination witU electron density available from neighboring atoms. Atomic hydrogen may bridge or otherwise be stabiUzed by two or more metal atoms. The mechanism of binding becomes less chemical and more physical in nature as bond formation becomes less important and electrostatic and intermolecular forces become more important. The binding energy of atomic hydrogen may be conceptually viewed in terms of a potential energy landscape that is characteristic of a hydrogen storage alloy. This potential energy landscape represents the spatial distribution of the binding energy of atomic hydrogen as a function of position within a hydrogen storage alloy. Examination of the potential energy landscape reveals a series of potential wells that correspond to hydrogen storage sites. The depth of the potential well associated with a hydrogen storage site is a measure of the binding strength of the site, while the width of the potential well is a measure of the spatial extent of the site. The depth and width of a potential well are reflections of the local electron density available for stabilizing hydrogen. Hydrogen storage sites that form direct metal-hydrogen bonds typically have deep and narrow potential wells that reflect the high binding strength and spatially localized nature of the metal-hydrogen bond formation mechanism of stabilization. As the available electron density decreases and stabilization occurs over a greater number of atoms, the potential well of a hydrogen storage site becomes wider and shallower.

The ability of a hydrogen storage site to retain atomic hydrogen depends on the depth of the potential well of the site and the thermal energy available to atomic hydrogen. The depth of a potential well corresponds to an activation barrier to motion of hydrogen trapped in the well and the available thermal energy is a measure of the ability of atomic hydrogen to overcome this activation barrier. Upon its formation, atomic hydrogen migrates through the hydrogen storage alloy and interacts with the potential energy well of one or more hydrogen storage sites. When the hydrogen encounters a potential well, its motion slows as it is trapped by the potential well. Spatially, the hydrogen is located at the minimum of the potential well and has a stabiUzation or binding energy that correlates with the depth of the potential well. The depth of the potential well presents an activation barrier to movement of the trapped hydrogen away from the hydrogen storage site. In order to move, the thermal energy available to the trapped hydrogen must be sufficient to overcome the activation energy of the hydrogen storage site. If the trapped hydrogen overcomes the activation barrier, it continues to migrate through tUe Uydrogen storage alloy until it is trapped at anotUer Uydrogen storage site or reacts at a catalytic site. If tUe tUermal energy available to trapped Uydrogen is insufficient, tUe trapped Uydrogen remains at tUe site and becomes stored at tUe site. Stored hydrogen can be released by increasing the temperature to make additional thermal energy available to the stored hydrogen. The additional thermal energy aUows the stored hydrogen to overcome the activation energy of the potential well. The amount of additional thermal energy required depends on the depth of the potential well.
From the viewpoint of the potential energy landscape, the design goal of releasing hydrogen at lower temperatures corresponds to creating hydrogen storage sites having potential wells with binding energies that permit the release of stored hydrogen at a preferred operating temperature. This goal requires creating hydrogen storage sites having shallower potential wells relative to existing hydrogen storage alloys. Decreasing the binding energy of a hydrogen storage site requires a reduction in the electron density that provides the stabiUzation necessary to store atomic hydrogen. In conventional hydrogen storage alloys, the electron density is varied by varying the chemical composition of the alloy. Different metal atoms have differing numbers of electrons, differing valence orbital occupancies and form bonds of different strength and orientation to other metal atoms. By combining metal atoms in unique ways to form new alloys, it becomes possible to exercise a degree of control over electron density and the binding energies of hydrogen storage sites in equilibrium hydrogen storage alloys. The instant materials represent a new class of hydrogen storage materials that include a fundamentally new type of hydrogen storage site that can be readily configured to provide a binding energy suitable for releasing hydrogen at any desired operating temperature. A characteristic feature of the hydrogen storage sites of conventional hydrogen storage alloys is the dominant presence of hydrogen storage sites in the bulk, as opposed to surface, phase of the alloy. The binding energies of the hydrogen storage sites are accordingly determined by the bulk properties of the hydrogen storage alloy. The bulk phase properties of a material are the properties that a material exhibits in the macroscopic regime. In practical terms, the macroscopic regime of most materials is reached for length scales beyond a few hundred to several hundred angstroms. Bulk material properties are the properties manifested by a large ensemble of atoms.

In the hydrogen storage sites of conventional hydrogen storage alloys, the binding energies associated with the potential wells are a consequence of the bulk properties of the hydrogen storage alloy. Extended metal-metal bonding and the formation of a metallic band structure are bulk characteristics of existing Uydrogen storage alloys tUat influence tUe potential wells of hydrogen storage sites. A metalUc band structure is the result of tUe metalUc bonding tbat occurs wUen a bulk ensemble of metal atoms comes togetber to form a soUd. A metalUc band structure is cbaracterized by empty, but readily accessible, conduction band states tUat correspond to spatially extended molecular orbitals. The molecular orbitals are quantum mechanical combinations of valence atomic orbitals of the individual atoms of the bulk ensemble of atoms that combine to form the hydrogen storage alloy. Since the conduction band states are essentially delocalized over the entire material, an electron promoted from any metal atom to the conduction band is essentially shared by aU atoms. This is a characteristic feature of metalUc bonding. In the context of hydrogen storage sites, a metallic band structure has the effect of deepening potential wells and increasing the binding energy of stored hydrogen. These effects are a consequence of the large number of metal atoms that influence the electron density present at a hydrogen storage site through the extended conduction band states. Metallic bonding leads to a sharing of electron density over large distances.
In order to reduce the number of metal atoms that influence a particular hydrogen storage site, tUe instant inventors have reasoned that it is necessary to disrupt the metalUc bonding tUat is characteristic of tUe Uydrogen storage sites of existing Uydrogen storage alloys. Since metalUc bonding is a consequence of extended metal-metal bonding over macroscopic lengtb scales, tUe instant inventors Uave further reasoned tUat a reduction in tUe number of atoms influencing or surrounding a Uydrogen storage site provides a new degree of freedom in controlling tUe binding energy of Uydrogen storage sites. More specifically, if tUe number of atoms can be reduced to tbe extent tUat bulk properties are not manifest, tben tUe extended metal-metal bonding required for metallic bonding cannot occur and the electron density at a hydrogen storage site is reduced. The binding energy of the site can therefore be reduced.
The extent to whicU the binding energy of a hydrogen storage site can be reduced depends on the extent to which metallic bonding is inhibited or precluded. In order to disrupt metallic bonding, it is necessary to create aggregates of metal atoms having length scales that are insufficient to permit attainment of bulk phase properties. The instant materials are comprised of an assembly of atomic aggregations having length scales in the quantum regime. The quantum regime is a sub-macroscopic regime characterized by atomic aggregations having length scales on the order of a few angstroms to several tens of angstroms. The quantum limit corresponds to a unique state of matter Uaving electronic, cUemical, pUysical or otUer properties not found in the macroscopic limit. Quantum scale aggregations possess structural degrees of freedom not available in macroscopic scale aggregations due to a Ufting of tUe constraints imposed in tUe macroscopic limit. Due to a relaxation of structural constraints, quantum scale aggregations are able to adopt structural configurations not available in macroscopic materials. Deviations from tUe bond angles, bond lengtbs and otUer structural variables tUat are standard in conventional materials become possible in tUe quantum limit.

Atomic aggregations in the quantum limit are able to adopt a wider range of structural configurations due to diminisbment of structural rigidity tUat occurs as tUe number of atoms in an aggregation is reduced. This greater topological flexibiUty results from a reduction in tUe resistance to structural rearrangement and distortions as the number of atoms in an aggregation is reduced. A large number of atoms imposes constraints on tUe topology and range of structures available for a material due to tUe need to mutually satisfy tUe bonding requirements of eacb of the atoms in the aggregation. The structure of continuous atomic aggregations must also be space filling and this requirement also constrains the allowed configuration of atomic aggregations. Although amorphous materials show greater flexibility and diversity in local structure than crystalline materials, conventional amorphous materials are nonetheless spatially extended over macroscopic length scales, require space fiUing as well as mutual satisfaction of local bonding requirements of a large number of atoms and tUus do not permit full reaUzation of tUe range of structural configurations available to smaller assemblages of atoms.
Tbe space filling and bonding requirements of macroscopic scale materials underUe tbe ubiquitous occurrence of the famπiar Unear, trigonal, tetrahedral, octabedral etc. bonding configurations of atoms in materials. In tUe absence of defects, deviations from regular bonding occur to some extent in the amorphous phase, but to a greater extent at the surface of a material. Surface atoms are partially unbonded due to the absence of atoms beyond the surface of a material. Surface atoms are accordingly bonded to fewer atoms than interior or bulk atoms of a material and therefore exhibit greater diversity in structure and bonding. Configurational parameters such as bond angles, bond lengths, hybridization, coordination number etc. vary over a wider range for surface atoms than bulk atoms and greater richness in topology and properties occurs as a result. As the number of surface atoms relative to bulk atoms increases for an aggregation of atoms, the structural diversity and structural degrees of freedom available increases. In one viewpoint, the quantum limit may be viewed as a limiting structural configuration in wUicU atomic aggregations approacU or acUieve configurations in wUicU most or all atoms are surface atoms. The structural flexibility and variabihty in structural configuration increases accordingly.
In addition to and in concert with new structural degrees of freedom, the quantum limit also provides mechanisms for controlUng or regulating tUe quantity and spatial distribution of electron density in the vicinity of catalytic sites. The greater ability to control structural configurations of atomic aggregations in the quantum limit provide a mechanism for modifying electron density at catalytic sites, thereby permitting unprecedented control over catalytic properties. The quantity and distribution of electron density within a catalyst and at catalytic sites ultimately originates from the wavefunctions and overlap thereof associated with the orbitals of the constituent atoms in an aggregation of atoms. The quantity and distribution of electron density at particular points such as catalytic sites within a catalytic material can be modified through electronic interactions that may occur between or among atoms. In quantum mechanical terms, the electronic interactions between atoms of a catalyst may be described in terms of an overlap of wavefunctions. The catalytic sites of a catalytic material are collections of atoms that are chemically bonded or physically connected where the electron density of each atom is describable by one or more wavefunctions. The electronic interaction present in the instant materials corresponds to the development of an overlap between wavefunctions of two or more atoms within the instant quantum limit aggregations.
The general effect of electronic interaction through wavefunction overlap between atoms comprising the instant quantum Umit aggregations is to perturb, redistribute or otherwise modify the magnitude and distribution of electron density. The specific effect of the electronic interaction present between the atoms depends on the strength and nature of the overlap of wavefunctions. As is known in quantum mechanics, the overlapping of wavefunctions (e.g. superpositions or combinations) may lead to the formation of bonding and/or anti-bonding orbitals. Bonding orbitals typically lead to an increase in electron density in the space between the interacting atoms associated with the overlapping wavefunctions. Such a bonding type electronic interaction results in a delocalization of electron density from one or more of the interacting atoms to others of the interacting atoms or to the space between the interacting atoms.
Anti-bonding orbitals formed by overlapping wavefunctions typically lead to a decrease in electron density in the space between the interacting atoms associated with the overlapping wavefunctions. Such an anti-bonding type electronic interaction prevents delocalization of electron density to tUe region between tbe interacting atoms associated with the overlapping wavefunctions. Instead, a repulsive type effect results that leads to a reduction in the spatial extent of electron density emanating from one or both of the interacting atoms. Electron density residing in the interacting atoms becomes more locaUzed and leads to an increase in electron density in tUe vicinity of the interacting atoms relative to a situation in which no anti-bonding electronic interaction is present.
In the instant quantum Umit catalysts, electronic interaction due to wavefunction overlap may occur in which electron density delocalizes from or localizes on one or more catalytic sites. Modification of electron density may occur tUrougU tUe bonding or anti-bonding mecbanisms as described bereinabove as well as tUrougU donor-acceptor type electronic interactions or tunneling type electronic interactions. A donor-acceptor interaction is an interaction between orbitals or wavefunctions of atoms within an atomic aggregation in whicU at least one of tUe interacting wavefunctions is unoccupied or only partly occupied. A donor-acceptor interaction is one in wUich electron density is transferred from the donor to the acceptor where the acceptor receives the transferred electron density in a partially occupied or unoccupied orbital. Tunneling is a quantum mecUanical process in wUicU electron density delocalizes from one atom to anotUer tUrougU penetration of an energy barrier. Tunneling is tUe basis of well-known effects sucU as field emission and scanning tunneling microscopy and is a consequence of the quantum mechanical tendency for electron density to extend beyond the physical boundaries of atoms.

The catalytic properties of a catalytic site are largely determined by the distribution of electron density at or near the site. Catalytic functionality requires an abiUty of catalytic sites to attract and stabilize one or more reactant species for a period of time sufficient to permit a cUemical reaction or molecular rearrangement to occur. TUe electron density at or near tUe catalytic site influences tUe strengtU of interaction between tbe catalytic site and potential reactants and also influences factors such as the geometric position or orientation of a reactant on the surface of a catalytic material.
The electronic interactions present in the instant quantum limit materials provide new degrees of freedom for modifying the distribution of electron density at or near catalytic sites. The strength and type (e.g. bonding, anti-bonding, donor-acceptor, tunneling) of the electronic interaction in the quantum limit ultimately depends on tUe extent and nature of wavefunction overlap between the atoms comprising a quantum Umit aggregation. The extent and nature of overlap depend on several factors. First, the spatial extent of the wavefunctions associated with the electron density of interacting atoms influences the extent of overlap. Of particular relevance is the extent to which the wavefunctions contributing to the overlap extend beyond the physical boundaries of the interacting atoms. Tightly bound electron density is described by wavefunctions that are essentially contained within the boundaries of the aggregate of atoms from which the wavefunctions originate. Such wavefunctions show little tendency to spatially overlap wavefunctions originating from nearby aggregates of atoms. Atoms wUose wavefunctions extend beyond tUe pUysical boundaries of tbe aggregate of atoms from wUicU the wavefunctions originate, in contrast, show greater tendency to exhibit the spatial overlap or barrier penetration necessary to provide the electronic interaction of the instant invention. Generally speaking, wavefunctions associated with electron density corresponding to higher energy occupied atomic and/or molecular orbitals are more spatially extensive than wavefunctions associated with lower energy orbitals. As orbital energy decreases, electrons on atoms become more tightly bound and interact to a lesser degree with electrons on neighboring atoms. Wavefunctions showing greater spatial extent are also more likely to participate in tunneling interactions tiian wavefunctions tUat are tightly bound.
A second factor contributing to the extent and nature of wavefunction overlap is the relative orientation of the interacting wavefunctions of the atoms comprising the instant quantum limit atomic aggregations. Wavefunctions are typically spatially non-isotropic and have characteristic directionality and reflect asymmetries of electron density. Even if wavefunctions show great spatial extent, the regions of space occupied by the wavefunctions of interacting must be co-extensive in order to create spatial overlap and to produce the electronic interaction of the instant invention. The requirement for spatial co-extensiveness is tantamount to a directionaUty or wavefunction orientation requirement.

Wavefunction directionaUty is also relevant to tunneling since electron density tUat penetrates a barrier must delocalize onto adjacent atoms through the occupation of orbitals.
The structural flexibility provided in the quantum Umit increases tUe likelihood of achieving wavefunction directionality conducive to spatial overlap and tunneling. TUe directionality of wavefunctions is intimately connected witU tUe structure of a group of atoms. A mutual dependence exists between the structural configuration of a group of atoms and wavefunction directionality since tUe spatial orientation of wavefunctions is cUaracteristic of tUe bonding scbeme tUat occurs between tbe atoms of an atomic aggregation. By providing new degrees of freedom in atomic configuration and topology, tUe quantum limit provides for wavefunction orientations not possible in conventional macroscopic scale materials and tUerefore provides for tUe creation or modification of wavefunction overlap and/or tunneling not otUerwise possible. Novel catalytic properties accordingly result.
A tbird factor contributing to tUe extent and nature of wavefunction overlap is tUe relative energy of tUe interacting wavefunctions of tUe atoms comprising tUe instant quantum Umit aggregations. It is known from quantum mecUanics tUat tUe relative energies of wavefunctions Uaving adequate spatial extent and suitable orientation influences tbe strengtU of interaction between tbe wavefunctions and the resulting effect on electron density. The closer in energy the interacting wavefunctions are, the stronger is their strength of interaction. Wavefunctions having identical or similar energies show stronger interactions than wavefunctions having dissimilar energies. A stronger electronic interaction between wavefunctions indicates a greater degree of mixing of wavefunctions from the catalytic phase and the support matrix to provide a new wavefunction that better reflects a combination of the properties of the properties of interacting atoms. As the mismatch in energy between contributing wavefunctions increases, mixing may still occur, but the resulting wavefunctions exUibit cUaracteristics tUat are predominantly controlled by tUe wavefunctions of the individual contributing atoms.
A fourth factor contributing to tUe extent and nature of wavefunction overlap is tUe relative phases of the interacting wavefunctions. The wavefunction phase can be positive or negative and the relative phases of the wavefunctions of the interacting atoms influences wUetUer tUe electronic interaction is, for example, of tUe bonding type or anti-bonding type. Wavefunctions Uaving tUe same pUase interact to provide a new wavefunction of tUe bonding type and result in a bonding-type electronic interaction between the atoms of a catalytic site. Wavefunctions having opposite phase interact to provide a new wavefunction of the anti-bonding type and result in an anti-bonding type electronic interaction between atoms of a catalytic site.
One or more catalytic properties may be improved through the electronic interactions present in the quantum limit atomic aggregations of the instant materials. These catalytic properties include reaction rate, overall catalytic activity, selectivity, range of catalytically affected reactants, and the range of environmental conditions under which catalytic effects are observed. Overall catalytic activity refers to the rate of reaction and/or the conversion efficiency of a catalyst. Selectivity refers to the ability of a catalyst to discriminate among potential reactants wUen in tUe presence of a plurality of reactants. Oftentimes a catalytic reaction is preferentially completed on a particular component witUin a mixture of components. Range of catalytically affected reactants refers to tUe range of cUemical species tUat undergo a catalyzed reaction in tUe presence of a catalyst. Catalysis of a particular species may become possible through the electronic interaction of the instant materials where said species was not catalyzed by the same catalytic phase in the macroscopic limit. TUe range of environmental conditions refers to external conditions sucU as temperature, pressure, concentration, pH, etc. under which a particular catalytic reaction may occur. The electronic interaction of the instant quantum limit catalyst may facilitate catalytic function at conditions tUat are more convenient tUan tUose for tUe corresponding reaction in the presence of a conventional catalyst in the macroscopic limit. TUe reaction temperature, for example, may be lowered tUrougU use of tUe instant catalytic materials. Similarly, tUe catalytic activity at a particular temperature may be greater for a particular reaction tUrougU use of tUe instant quantum limit catalytic materials. Of particular note in tUe context of tUe instant invention is tUe possibiUty of inducing a catalytic effect in a catalytic pUase wUere said catalytic pUase exUibits no catalytic activity witU respect to a particular reaction or process at a particular set of conditions in tUe macroscopic limit. Electrochemical, cUemical, tUermal, bond cleavage, bond formation,
rearrangements, isomerizations and otUer types of reactions are witUin the scope of the instant invention.

In terms of Uydrogen storage materials, tUe new structures acnievable in tUe quantum Umit lead to novel distributions of electron density and provide Uydrogen storage sites Uaving binding energies tbat provide lower desorption (release) or absorption (uptake) temperatures and/or faster desorption or absorption kinetics at a particular temperature relative to conventional Uydrogen storage materials. TUe binding energy of a storage site may be reduced in the quantum limit in a number of ways. In one embodiment, tbe bond lengtb between adjacent metal atoms in tbe instant materials is increased in tUe quantum limit relative to tUe bond lengtb of tUe corresponding bond in tbe macroscopic limit. A longer bond lengtb leads to a dilution of electron density and a weakening of tUe interaction of tUe bond witb Uydrogen due to an enlargement of tUe volume occupied by the electrons in the bond. As a result, the strength of interaction between the storage site and atomic hydrogen decreases. In another embodiment, the bond angles between neighboring atoms are increased or decreased relative to corresponding bond angles in the macroscopic Umit. Deviations in bond angles lead to a reduction in the extent of orbital overlap, a reduction in bond strength and rearrangement of electron density away from a hydrogen storage site. As a result, the interaction strength of the bond witb atomic Uydrogen decreases. In anotUer embodiment, tUe instant materials include bonds between metal atoms tbat are unable to bond in conventional hydrogen storage materials due to structural limitations imposed in tUe macroscopic Umit. TUe instant quantum limit Uydrogen storage materials include materials tUat Uave catalytic sites and Uydrogen storage sites. TUe catalytic and Uydrogen storage sites may be contained witUin a common atomic aggregation, different atomic aggregations or a combination thereof. The catalytic sites may be included in atomic scale aggregations or macroscopic scale aggregations. In the latter scenario, the instant materials include macroscopic catalytic regions in combination with quantum scale atomic aggregations for hydrogen storage where the catalytic regions may be of the same or different chemical composition than the hydrogen storage regions. Catalytic properties of hydrogen storage materials may include rate of hydrogen absorption or desorption as well as hydrogen storage capacity.
The instant catalytic and hydrogen storage materials preferably comprise transition metals, rare earth metals or a combination thereof. Single element as well as multi-element atomic aggregations in the quantum limit are witUin tUe scope of tUe instant invention. Preferred embodiments include quantum limit materials comprised of Ni or Ni alloy, Mg or Mg alloy, V or V alloy, Co or Co alloy, or Mn or Mn alloy.
In order to best reaUze tUe benefits of tbe quantum limit, tUe atomic aggregations of the instant materials preferably are metal or metal alloys in the form of particles having a size of 100 A or less. More preferably, the catalytic metal or metal alloy particles have a size of 50 A or less. Most preferably, the catalytic metal or metal alloy particles have a size of 20 A or less. As described hereinabove, as the size of a catalytic atomic aggregation decreases, the structural flexibiUty increases and new structural configurations result tUat reflect and provide novel distributions of electron density at catalytic sties tUrougU electronic interactions resulting from wavefunction overlap, wavefunction directionality and/or tunneUng effects not achievable in the macroscopic limit.
The instant quantum limit alloys may be viewed as virtual alloys in the sense that although they are comprised of chemical elements that are currently used in conventional catalytic materials, the novel structures, topologies and configurations available in the quantum limit provide for distributions of electron density, electronic interactions, wavefunction overlap and wavefunction directionaUty not achievable in the macroscopic limit. Since the spatial distribution of electron density and the orientation of orbitals constitute the essence of what a chemical element is, the modifications in electron density and wavefunction characteristics of atoms provided by the instant invention are tantamount to the creation of "new" chemical elements. These "new" chemical elements are virtual elements that are produced through the manipulations of the local environment that occur in the quantum limit and constitute an extension of Ovshinsky' s principle of total interactive environment discussed hereinabove. The instant materials exploit the new chemical and physical effects attainable through the combining of virtual elements to form virtual alloys having heretofore unachievable catalytic properties.
A further aspect of the virtual alloy concept is the possibility of forming alloy compositions that cannot be formed in macroscopic scale materials. It is well known in conventional materials that there are limitations on tUe cUemical compositions of alloys. CUemical bonds do not ubiquitously form between arbitrary pairs or collections of atoms. Instead, bonding is element specific and eacb element preferentially bonds with certain elements and is unable to bond with other elements. Bonding preferences are dictated by the electronic interactions and wavefunction characteristics of the elements. Since the virtual elements created in the quantum limit possess non-conventional electronic interactions, wavefunction characteristics, and electron density perturbed in magnitude or spatial distribution relative to conventional elements, the materials of the instant invention provide for the formation of chemical bonds between pairs or combinations of elements that are unable to bond in the macroscopic Umit. Thus, in addition to modified structural and electronic properties, the catalytic materials of the instant invention further provide for chemical compositions that are not possible in the macroscopic Umit.
As indicated hereinabove, the catalytic phase of the instant supported materials are preferably metals or metal alloys in the form of particles. More preferably, the catalytic particles comprise a transition metal and most preferably the catalytic particles comprise Ni. Transition metals are preferred because their valence electronic structure includes d-orbitals. As previously described by the instant inventor, d-orbitals provide for chemical modification effects through the concept of total interactive environment that lead to novel electronic environments in hydrogen storage materials. Further discussion of the concepts of chemical modification and total interactive environment may be found in the co-pending parent appUcation (U.S. Pat. Appl. Ser. No. 10/405,008) as well as in U.S. Patent Nos. 4,431,561; 4,623,597; 5,840,440; 5,536,591; 4,177,473; and 4,177,474 of wUicU the instant inventor is a co-inventor; the disclosures of which are herein incorporated by reference. In the instant invention, the concept of total interactive environment is extended to supported catalytic materials through the electronic interaction between the catalytic phase and support matrix due to wavefunction overlap as described hereinabove. d-orbitals facilitate wavefunction overlap because tbey are generally spatially well extended and are capable of hybridizing in many ways to achieve a variety of different spatial orientations. Transition metals thereby faciUtate the estabUshment, activation or inducement of the electronic interaction of the instant materials.

TUe instant quantum limit catalytic and hydrogen storage materials may be prepared in several ways. In one embodiment, an ultrasonic preparation is used. In this embodiment, sound waves are used to induce sonochemical reactions of starting materials. Sonochemistry is method whereby sound waves are used to drive an acoustic cavitation effect that induces chemical reactions. Acoustic cavitation refers to a process involving the formation, growth and collapse of bubbles in a liquid pUase medium. Bubble collapse is the driving force behind sonochemistry because bubble collapse is accompanied by intense local heating and high pressures over short time scales. The positions at which bubble collapse occurs may be viewed as local hot spots in the liquid pUase reaction medium. It is at tUese Uot spots that reactions occur. Representative conditions at the hot spots include temperatures of up to several thousand degrees, pressures of up to hundreds to tUousands of atmospUeres (comparable to pressures at the deepest points of an ocean), and heating and cooling rates on tUe order of up to a bilUon degrees per second. TUe actual conditions depend on tUe intensity and frequency of sound waves employed in a sonocUemical process. TUe extreme conditions are a consequence of the channeUng or localization of tUe energy of sound waves locally at tUe Uot spots and it is tUese extreme conditions tUat are responsible for the wide variety of chemical reactions possible in a sonochemical process. Sonochemical reactions may be completed in a homogeneous liquid pUase, Ueterogeneous liquid pUase (e.g. liquid pUase suspensions or incompletely miscible liquids), or Ueterogeneous Uquid-solid systems (e.g. slurry).

SonocUemical reactions are preferably completed in a homogeneous liquid pUase medium or slurry. Typically, one or more precursors (reactants, starting materials) is dissolved in a solvent and tUe mixture is sonicated (subjected to sound waves). Since tbe primary sonocUemical reaction site is in tUe vapor pUase of a bubble, it is preferable for the precursors to have a high vapor pressure and for the solvent to have a low vapor pressure. These conditions insure that the bubbles formed upon sonication contain, to the maximum extent possible, precursors, rather than solvent, and lead to higher sonochemical reaction efficiencies.
In the preparation of the instant quantum limit catalytic and Uydrogen storage materials, tUe preferred sonocUemical precursors are organometalUc compounds. TUese compounds include one or more transition metals tUat are coordinated by one or more ligands. Virtually any soluble
organometalUc precursor is suitable for reaction in a sonochemical process. Representative organometalUc precursors include metal carbonyls, metal alkyls, metal cyclopentadienyl compounds, and metal nitrosyls. In tUe sonocUemical reaction of tUese precursors, sonication leads to tUe decomposition of tUe precursor through cleavage of metal- ligand bonds to liberate metal atoms that subsequently agglomerate to form the quantum scale atomic configurations of the instant materials. In the instant invention, individual precursors may be sonicated to obtain product materials that include quantum scale aggregates of a single metal (quantum scale metals) or combinations of precursors may sonicated to obtain quantum scale metal alloys. Preferred solvents are those having high boiling points (e.g. long chain alkanes or alcohols).
In another embodiment, the instant quantum limit catalytic and Uydrogen storage materials are prepared tUrougU reduction reactions of metal salts. In tUese reactions, metal salts are precursors tUat are used to provide the metal atoms for a quantum limit metal or metal alloy. The metal salt precursors include metals in oxidized form that become reduced during reaction with a reducing agent to form neutral metal atoms that agglomerate to form the angstrom scale aggregations characteristic of the instant quantum limit materials. Alloy formation occurs through tUe simultaneous reduction of two or more metal salts.
In a typical reaction, one or more metal salts are reacted witU a reducing agent in a Uquid pUase solvent. Metal salts include salts tUat are soluble, insoluble or partially soluble in tbe solvent.
Representative metal salts include Ualides, nitrates, sulpUates, pUospUates etc. In a preferred embodiment, metal chlorides are used metal precursors. Preferred reducing agents include borohydrides or organoborates (e.g. hydrotriorganoborates such as NaB^Hs^H). Preferred solvents are liquids in wUicU tUe reducing agent is at least partially soluble.
In yet anotber embodiment, the instant quantum Umit catalytic and hydrogen storage materials are prepared in a thermal decomposition process. In this embodiment, a molecular precursor containing one or more metal atoms is thermally decomposed to liberate metal atoms tbat subsequently agglomerate to form quantum scale atomic aggregates. Preferred precursors are molecular systems having low decomposition temperatures. OrganometalUc precursors, for example, are desirable precursors because tbey include organic ligands tUat fragment under mild heating conditions. Metal-carbon and metal-nitrogen bonds, for example, typically cleave thermally at temperatures of 100 - 200 °C. Representative organometalUc precursors include metal alkyls, metal chelates, metal amines, metal aryls etc.
In tUe tUermal decomposition process, an organometalUc precursor compound may be Ueated to decomposition in eitUer a closed container or a flow reactor. In one embodiment, tbe precursor is a solid tUat is sublimed to form a gas phase reactant that subsequently decomposes thermally. The subUmed precursor is typically diluted witU a carrier gas in a continuous flow process or decomposed in a gas ambient in a closed reactor. The precursor may also be diluted with an organic compound, the thermal decomposition reaction, the organometalUc precursor decomposes to form a soUd metal or metal alloy product along witii one or more gas phase products (e.g. H2, N2, CO, C02, NO etc.) and sometimes a solid carbonaceous product. Multiple precursors that contain different metals or Ugands may be reacted simultaneously. The reaction conditions of the decomposition process can be designed to control the size and distribution of quantum scale aggregates within the instant materials.
EXAMPLE 1
In this example, the preparation and properties of a quantum limit iron catalyst is described. The catalyst includes atomic aggregations of Fe and is prepared using sonochemical synthesis. Iron carbonyl (Fe(CO)5) was used as the iron precursor. 19.5 g of iron carbonyl was placed in 80 mL of decahydronaphthalene (DecaUn) in a beaker and subjected to sonication. The iron carbonyl was protected from air and the sonication was completed in a dry box under a nitrogen atmosphere. A 750 W sonicator operating at 75% intensity was used to provide the'ultrasound used in the synthesis.

Sonication occurred for 8 hours using a 50% duty cycle (ultrasound was alternated on and off in equal time intervals over the 8 hours). Upon termination of the reaction, 0.5 g of quantum Umit iron product was recovered. The product was analyzed using X-ray diffraction (XRD) and found to consist of aggregations of Fe having an average size of 16 - 20 A.

TUe Uydrogen absorption and desorption characteristics of the quantum Umit Fe obtained in the sonochemical synthesis were investigated in a PCT (pressure-composition-temperature) experiment. The PCT measurement was completed at 90 °C. Two samples were compared. A first sample was a control sample that consisted of an Mg based hydrogen storage alloy. A second sample was a mechanical alloy (MA) of the control sample with 0.50 wt.% of the quantum limit Fe.
The control sample was an alloy comprising primarily Mg and Ni and smaller amounts of other transition metals and boron. The control sample was prepared by combining raw materials representing the desired alloy composition in a boron nitride crucible within a melt spinning chamber. Since Mg is volatile at high temperatures, excess magnesium was added in an amount necessary to compensate for evaporative losses. The crucible temperature was ramped up to a temperature over 1000 °C over a time period of about 40 minutes to form a melt. A plug at the bottom of the crucible was subsequently removed to allow tbe melt to flow from tUe crucible toward a l igb speed, water-cooled Be-Cu alloy melt-spinning wUeel rotating at a linear speed of about 10 m/s. TUe melt is quencUed and solidified to form ribbons of the alloy material when it hits the wheel. The ribbons of the alloy were collected and allowed to cool for more than 12 hours. After cooUng, tUe alloy was transferred under a protective argon atmospUere to an attritor for mecUanical alloying. Grapliite and heptane were included as grinding aids and grinding was performed for two hours to form the control sample of this experiment. A second sample was prepared in a similar manner except that quantum Umit Fe was added to the attritor for the last ten minutes of grinding.
PCT curves for the two samples on absorption and desorption of hydrogen were measured using a standard PCT apparatus. The results of the experiment are shown in Fig. 1, where MA QL Fe refers to the mechanical alloy of the control sample with quantum limit Fe as described above. The results for each sample are denoted with different symbols, as indicated in the legend. The plot shows the hydrogen pressure as a function of absorption wt.% where absorption wt.% is a measure of the amount hydrogen absorbed by the sample. The general appearance of the data curves for each of the samples is similar and each data curve consists of a hydrogen absorption portion and hydrogen desorption portion. The hydrogen absorption portion is an upward sloping curve beginning near 0 wt% and continuing up to an approximate saturation point as the absorption wt.% increased. After saturation, desorption was initiated. The desorption portion of the data curves begins at the saturation point and slopes downward in the direction of decreasing absorption wt.%. The hydrogen absorption wt.% and hydrogen desorption wt.% for each sample are reported in table form below the data plot. The reported hydrogen absorption wt.% of each sample corresponded to the approximate saturation point and the reported hydrogen desorption wt.% of each sample corresponded to the amount of hydrogen lost and was measured as the difference in absorption wt.% between the saturation point (initial point of the desorption portion of the data curve) and the terminal point of the desorption curve.
The experimental results show that inclusion of quantum Umit Fe in tUe Uydrogen storage material improved tUe Uydrogen absorption relative to the control sample. The wt.% absorbed hydrogen increased from 2.113 for the control sample to 2.396 for the mechanical alloy of the control sample with the instant quantum limit Fe catalyst. TUe UigUer Uydrogen absorption is a consequence of the greater overall catalytic activity provided by the quantum Umit Fe relative to a Fe catalyst in the macroscopic Umit. The quantum limit Fe facilitates the catalytic dissociation reaction of hydrogen gas to form atomic hydrogen for storage and/or provides a greater concentration of hydrogen storage sites. Inclusion of quantum Umit Fe did not benefit the desorption characteristics of the material in this experiment, however. The wt.% desorbed hydrogen decreased from 0.498 wt.% to 0,129 wt.% upon inclusion of the quantum Umit Fe.
TUis example sUows tUat the instant quantum limit Fe faciUtates tUe Uydrogen absorption properties of a Uydrogen storage material.
EXAMPLE 2
In this example, the preparation and properties of a quantum Umit Mg catalyst are described. Conventional Mg is a well known hydrogen storage material that provides a particularly high hydrogen storage capacity due to strong bonds between Mg and H. The practical difficulty associated with conventional Mg is its poor hydrogen release (desorption) characteristics. Because of the high Mg-H bond strength, it is difficult to remove hydrogen from the storage sites of conventional Mg and accordingly high desorption temperatures are required.
The instant Mg catalyst was prepared through a thermal decomposition reaction.
Mg(anthracene)-2THF was used as the Mg precursor. The precursor was an orange soUd. 5.8 g of the precursor were sublimed under vacuum. At a temperature of ca. 40 °C, the THF was liberated from the precursor and at a temperature of ca. 150 °C, anthracene was subUmed to leave a fine Mg black powder. Analysis of tUe sublimation process indicated that 2.2 g anthracene were produced.and ca. 0.5 g of the Mg catalyst product was obtained. XRD analysis of the Mg catalyst indicated that it consisted of atomic aggregations of Mg having an average size of 40 nm. This size is much smaller than the ca. 1 micron size Mg particles used in conventional ball-milled Mg catalysts.
The hydrogen absorption and desorption characteristics of the Mg catalyst were determined. A noteworthy feature of the experiments is that the Mg catalyst was employed directly in an unactivated state. Due to otherwise poor absorption and desorption kinetics, conventional Mg is used in an activated state. Although activation improves the kinetics, it is preferable to avoid activation since it adds additional processing steps in catalyst preparation. Fig. 2 shows the hydrogen absorption characteristics of tUe Mg catalyst at tUree different temperatures. Fig. 2 shows the wt.% absorbed hydrogen as a function of time for temperatures of 30 °C, 50 °C, and 150 °C. In the measurements, a sample of the Mg catalyst was placed in contact with hydrogen gas having a pressure of 390 psia. The sample was initially at 30 °C and was allowed to equilibrate. TUe temperature was tUen increased to 50 °C and tUe sample was allowed to re-equilibrate. Finally, the temperature was increased to 150 °C and allowed to re-equilibrate. The hydrogen absorption was measured repeatedly at each temperature to insure equilibration. The wt.% absorbed hydrogen was found to be ca. 0.19 at 30 °C, ca. 0.43 at 50 °C, and ca. 0.62 at 150 °C. The remarkable result of the experiment is the observation of a non-zero hydrogen absorption at 30 °C and 50 °C. Conventional Mg, even in an activated state, shows essentially no hydrogen absorption at 30 °C and 50 °C. The instant Mg catalyst, in contrast, shows measurable hydrogen absorption due to enhanced catalytic activity.
Figs. 3 and 4 show the absorption kinetics of the instant Mg catalyst, in unactivated form, at 250 °C and 300 °C, respectively. The figures show the hydrogen storage capacity (wt.% of absorbed hydrogen (upper curve at long time)) and the catalyst temperature (lower curve at long time) as a function of time. After a short term drop off upon initial exposure to hydrogen gas, die storage capacity shows a rapid increase at both temperatures before leveling off at or near an equilibrium value. At 300 °C, the equilibrium storage capacity is above 4.5%. Most of the equilibrium hydrogen content is stored in the first five minutes of exposure. At 250 °C, the equilibrium storage capacity is about 3.5% and is obtained after about 30 min. exposure. Tbe notewortUy feature of botU figures is tUe essentially instantaneous absorption of hydrogen upon exposure to hydrogen gas for a Mg based catalytic hydrogen storage material in an unactivated state. This behavior contrasts with conventional Mg alloys, which only show hydrogen absorption upon activation. The improved hydrogen absorption characteristics of the instant Mg catalyst are a consequence of an increased rate of hydrogen absorption for the instant quantum limit Mg catalyst relative to a conventional macroscopic Mg catalyst. TUe Uydrogen absorption observed for the instant unactivated Mg catalyst is a consequence of the improved catalytic activity resulting from the novel structure, topology, wavefunction characteristics, and electron density distribution associated with the quantum Umit.
EXAMPLE 3
In tiiis example, die preparation of a quantum Umit V catalyst is described. An organometalUc vanadium precursor, V(Cp)(CO)4 (Cp = cyclopentadienyl) is used in the preparation. 4.963 g of the vanadium precursor were placed in decane and refluxed until a black precipitate was formed. The precipitate was analyzed to be V and XRD and SEM analysis showed that the product consisted of aggregations of V having an average size of 40 A.
EXAMPLE 4
In this example, the sonochemical preparation of a quantum Umit Co catalyst is described. An organometalUc Co precursor, Co(CO)4(NO), was used as a starting material. The Co precursor was placed in DecaUn in a beaker and sonicated as described in EXAMPLE 1 hereinabove. Upon termination of the reaction, a black powder product was observed. XRD analysis indicated that the product was highly disordered and amorphous-Uke.
TUe instant invention further considers supported catalytic materials for general use in facilitating cUemical reactions, including reactions tUat produce Uydrogen. Conventional supported catalysts Uave been widely used to promote a variety of cUemical reactions. Conventional supported catalysts include a dispersed catalytic pUase tUat is supported on a support matrix. TUe role of tUe support matrix is to provide mecUanical support or stabilization of the dispersed catalytic phase. A conventional support is chemically and electronically inert with respect to the catalytic phase and merely provides a surface or structure upon which a catalytic phase can be formed and retained. A common method for preparing a conventional supported catalyst includes dissolving a precursor for the catalytic phase in a solution, depositing the solution on a support and forming the catalytic phase by allowing the solvent of the precursor solution to evaporate. The catalytic phase so formed is dispersed across the surface and pores of the support matrix. The interaction between the support matrix and the catalytic phase in a conventional supported catalyst is physical in nature. The support matrix functions as a substrate for holding or mechanically stabilizing a catalytic phase that is formed thereon through evaporation or some other method. The catalytic phase is akin to a layer, which is potentially heterogeneous and/or non-uniform, that conformally rests on the support. The catalytic properties of a conventional supported catalytic material are those that are intrinsic to the catalytic phase. Except for providing mechanical stabilization, dispersion and inhibiting aggregation, the support matrix has little or no influence on tUe catalytic properties of tUe catalytic pUase. TUe support matrix of a conventional supported catalyst is tUus referred to lierein as an inert or electronically inert support matrix.
TUe catalytic pUase of conventional supported catalysts is typically comprised of particles of a catalytic material. TUe beneficial properties of conventional supported catalytic materials accrue from the intrinsic catalytic properties of the catalytic phase in combination with the dispersed physical positioning provided by the inert support of the catalytic particles that comprise the catalytic phase. Dispersal of the catalytic phase prevents or inhibits aggregation of catalytic particles and improves catalytic performance by providing a high surface area for chemical reaction.
The instant invention is directed at creating next generation supported catalytic materials that have improved and/or heretofore unattainable catalytic performance. The instant invention provides a new degree of freedom in the design of supported catalytic materials to provide a new class of catalysts whose functionality extends beyond that of conventional supported catalytic materials. The instant catalytic materials are supported catalytic materials that include a catalytic phase and a support matrix where tUe support matrix provides more tUan simple mecUanical stabilization and physical dispersion of the catalytic phase. In the instant materials, the support matrix also interacts electronically with the catalytic phase to provide a mechanism for altering, enhancing or otherwise modifying the intrinsic catalytic properties of the catalytic phase. In the instant invention, an electronic interaction between the catalytic phase and support matrix is present and acts to modify the catalytic properties of the catalytic phase relative to a corresponding catalytic material that includes the catalytic phase supported by an electronically inert support matrix. The support matrix of the instant invention may hereinafter be referred to as an electronically active support matrix.
The catalytic phase of the instant materials is preferably a metal or metal alloy in the form of particles. The catalytic particles have a particle size distribution that is typically non-uniform and the catalytic particles are dispersed on the support matrix according to a spatial distribution. For a given particle size distribution and spatial distribution of catalytic particles on a support matrix, the electronic interaction between the catalytic particles and an electronically active support matrix provides for improved catalytic properties of the catalytic particles having the same particle size distribution and spatial distribution when supported by an inert support matrix. The electronic interaction of the instant invention may additionally create size and/or spatial distributions of catalytic particles not achievable on inert support matrices.
As in conventional supported catalysts, size influences the intrinsic catalytic properties of the catalytic particles. Smaller particles sizes provide higher surface area to volume ratios and are accordingly preferred since high surface areas promote catalytic activity. Sufficiently small particle sizes may also place a catalytic material into the quantum limit regime, tUereby providing unortbodox structure, bonding and catalytic sites. In addition to surface area and intrinsic catalytic activity, tbe size of tUe catalytic particles in tUe context of tUe instant invention furtUer influences the tendency of tUe catalytic pUase to interact electronically witU a support matrix. As used Uerein, electronic interaction refers to an interaction between a catalytic phase and an electronically active support matrix that involves a transfer or delocalization of electron density from tUe catalytic phase to the support matrix or from the support matrix to the catalytic phase or mutual transfer or delocaUzation between the catalytic phase and the support matrix. As used herein, electronic interaction may also refer to an interaction between a catalytic phase and a support matrix that involves an inhibition or localization of tUe spatial extent of electron density of tUe catalytic pUase and/or support matrix. As described more fully hereinbelow, the electronic interaction present in the instant materials arises from an overlap of the wavefunctions of electron density associated with the catalytic phase and an electronically active support matrix, where the overlap can lead to bonding or anti-bonding effects that may influence the electron density in the vicinity of or between the catalytic phase and support matrix. The delocalization or localization of electron density associated witU tUe electronic interaction of the instant materials distinguisUes tUe interaction of tUe catalytic pUase and tUe support from tUe Coulombic type electrostatic interaction tbat may be present in conventional supported catalysts. Whereas a Coulombic type interaction is physical in nature, delocaUzation or localization of electron density is cUemical in nature.
While not wisUing to be bound by theory, the instant inventor believes tUat tUe electronic interaction between the catalytic phase and electronically active support of the instant materials may be viewed in quantum mechanical terms. The cohesiveness of materials is ultimately due to chemical bonds that form between the atoms that comprise a material. Chemical bonds are essentially regions of electron density that stabiUze a collection of atoms. TUe electrons originate from atomic orbitals on atoms. The atomic orbitals of an atom, frequently in hybridized form, combine with atomic orbitals of neighboring atoms to form bonding and anti-bonding molecular orbitals. The stabilization associated with the occupation of bonding orbitals by electrons drives the formation of bonds and underUes the stability of materials.
In quantum mecUanical terms, the electron density associated with atomic and molecular orbitals can be described by wavefunctions and chemical bonding and anti-bonding can be described in terms of combining wavefunctions. The formation of bonding molecular orbitals from atomic orbitals results from the overlapping of the wavefunctions of atomic orbitals to produce new wavefunctions that may extend over multiple atoms. The extended wavefunctions signify the delocalization of electron density from one atom to other atoms in a material. The tendency for the electron density of an atom to delocaUze is related to tUe spatial extent of tUe wavefunction that describes the electron density and chemical bonding is related to the degree to which the wavefunction of one atom spatially overlaps the wavefunction of neighboring atoms. Wavefunctions that extend away from an atom show a greater tendency to overlap wavefunctions of neighboring atoms. Spatially locaUzed wavefunctions, in contrast, show little spatial extent and correspond to electron density that is closely held by or tightly bound to an atom. Tightly bound wavefunctions show little tendency to interact witU or overlap wavefunctions of neigUboring atoms. Electron density described by spatially extended wavefunctions is thus more likely to delocalize tUan electron density described by tightly bound wavefunctions.
Multi-electron atoms have multiple occupied atomic orbitals and form multiple molecular orbitals upon forming chemical bonds. Anti-bonding molecular orbitals may also form. The various atomic orbitals have varying spatial extents and show varying degrees of spatial overlap with atomic orbitals from neighboring atoms. It is generally accepted that the spatial extent of atomic orbitals increases in the following order: Is < 2s < 2p < 3s < 3p < 4s < 3d < 4p ... The outermost or valence electrons of an atom are generally the most spatially extended and therefore correspond to electron density having a wavefunction showing the greatest tendency to overlap spatially with wavefunctions from neighboring atoms to form bonding and/or anti-bonding molecular orbitals. Generally speaking, the spatial extent of a wavefunction increases as the energy of the orbital (atomic or molecular) increases. Higher energy electrons within atoms are thus more likely to locaUze or delocalize through interactions with neighboring atoms tUan are lower energy electrons.
TUe electronic interaction between the catalytic phase and electronically active support of the instant materials may be described in terms of an overlap of wavefunctions. The catalytic particles of the catalytic phase are collections of atoms that are chemically bonded with electron density describable by one or more wavefunctions. The support matrix is similarly a collection of atoms having its own electron density describable by a separate set of wavefunctions. The electronic interaction present in the instant materials corresponds to the development of an overlap between one or more wavefunctions of the catalytic particles and one or more wavefunctions of the support matrix.
The effect of the electronic interaction present between the catalytic particles and support matrix of the instant materials on the catalytic properties depends on the strength and nature of the overlap of wavefunctions. As is known in quantum mechanics, the overlapping of wavefunctions (e.g.
superpositions or combinations) may lead to the formation of bonding and or anti-bonding orbitals. Bonding orbitals typically lead to an increase in electron density in the space between the interacting entities associated with the overlapping wavefunctions. Such a bonding type electronic interaction results in a delocalization of electron density from one or more of the interacting entities to others of the interacting entities or to the space between the interacting entities. In the instant materials, a bonding type electronic interaction due to wavefunction overlap may occur in which electron density delocaUzes from one or both of the catalytic phase and support matrix.
It is to be understood in the context of the instant invention that a bonding type electronic interaction need not necessarily imply that a chemical bond forms between the catalytic phase and the support matrix. The attachment of the catalytic phase to the support matrix may remain physical or mechanical in nature in die presence of a bonding type electronic interaction. In this instance, a chemical bond per se may not form. The interaction is viewed as a bonding type of interaction when electron density delocalizes to or from the catalytic phase due to an overlapping of one or more wavefunctions of the catalytic phase with one or more wavefunctions of the support matrix. In the limit of a sufficiently strong bonding-type electronic interaction, a chemical bond may form between the catalytic phase and the support matrix.
Anti-bonding orbitals formed by overlapping wavefunctions typically lead to a decrease in electron density in the space between the interacting entities associated with the overlapping wavefunctions. Such an anti-bonding type electronic interaction prevents delocalization of electron density to tUe region between tUe interacting entities associated witU tUe overlapping wavefunctions. Instead, a repulsive type effect results tUat leads to a reduction in tUe spatial extent of electron density emanating from one or both of the catalytic phase and support matrix. Electron density residing in orbitals associated with the catalytic phase and/or support matrix becomes more localized and leads to an increase in electron density in the vicinity of the catalytic phase and/or support matrix relative to a situation in which no anti-bonding electronic interaction is present, hi the presence of an anti-bonding type electronic interaction, electron density originally associated with the catalytic phase and/or support matrix becomes denser and more localized.
TUe catalytic properties of tUe catalytic pUase are largely determined by the distribution of electron density at or near its surface. The catalytic phase of the instant invention is preferentially comprised of particles having catalytic activity where the catalytic activity depends on the electron density at or near the surface of the particles. Catalytic function requires an abiUty of catalytic particles to attract and stabilize one or more reactant species for a period of time sufficient to permit a cUemical reaction or molecular rearrangement to occur. TUe electron density at or near tUe surface of tUe catalytic particles influences tUe strengtU of interaction between the catalytic particle and potential reactants as well as factors such as the geometric position or orientation of a reactant on the surface of the catalytic particles. Catalytic reactions occur at selected sites on the surfaces of catalytic particles. These catalytic sites are catalytically active as a consequence of a favorable distribution of electron density. Effects that alter the distribution of electron density at or near the surface of a catalytic particle influence the catalytic activity.
The electronic interaction present in the instant materials, whether it be of the bonding-type or anti-bonding type, provides a new degree of freedom for modifying the distribution of electron density at or near the surface of the catalytic particles. A bonding-type electronic interaction may lead to a delocaUzation of electron density away from tUe surface of a catalytic particle and may result in a decrease in electron density at or near the surface of catalytic particles. An anti-bonding type electronic interaction may lead to a localization of electron density tUe vicinity of tUe surface of a catalytic particle and may result in an increase in electron density at or near tUe surface of tUe catalytic particles. By modifying tUe electron density at or near tUe surface of catalytic particles, tUe electronic interaction resulting from tUe wavefunction overlap present between tbe catalytic particles and support matrix of tUe instant materials provides a mechanism for modifying tUe catalytic properties of tUe catalytic phase and tUe supported material in general.
TUe strengtU and type (bonding vs. anti-bonding) of tbe electronic interaction in tUe instant supported catalytic materials ultimately depends on tUe extent and nature of wavefunction overlap between tbe catalytic pUase and electronically active support matrix. TUe extent and nature of overlap depend on several factors. First, tUe spatial extent of tUe wavefunctions associated witU tUe electron density of tUe catalytic pUase and support matrix influences tUe extent of overlap. Of particular relevance is the extent to which the wavefunctions contributing to the overlap extend beyond the physical boundaries of the catalytic phase and support matrix. Tightly bound electron density is described by wavefunctions that are essentially contained within the boundaries of the aggregate of atoms from which the wavefunctions originate. Such wavefunctions show little tendency to spatially overlap wavefunctions originating from nearby aggregates of atoms. Catalytic phases or support matrices having tightly bound wavefunctions show little tendency to overlap witU eacU otUer or otUer wavefunctions and consequently show little tendency to provide tUe electronic interaction underlying tUe enUanced catalytic properties of tUe instant invention.
Catalytic pUases or support matrices wUose wavefunctions extend beyond tbe pUysical boundaries of the aggregate of atoms from which the wavefunctions originate, in contrast, show greater tendency to exhibit the spatial overlap necessary to provide the electronic interaction of the instant invention. Generally speaking, wavefunctions associated with electron density corresponding to higher energy occupied atomic and/or molecular orbitals are more spatially extensive than wavefunctions associated with lower energy orbitals. As orbital energy decreases, electrons on atoms become more tightly bound and interact to a lesser degree with electrons on neighboring atoms. Electrons in higher energy orbitals are oftentimes referred to as valence electrons, while the more tightly bound electrons in lower energy orbitals are oftentimes referred to as inner core electrons.
Factors that influence the spatial extent of wavefunctions include the Lewis basicity of the catalytic phase and/or support matrix and the size of particles in the catalytic phase. Lewis basicity is a measure of the electron donating capability of tbe catalytic pUase and/or support matrix. Greater Lewis base strength of a catalytic phase and/or support matrix composition increases the likeliUood of spatial overlap of wavefunctions and of acUieving tUe electronic interaction of tUe instant invention.
TUe size of tUe particles of a catalytic pUase also influences tUe spatial extent of tUe wavefunctions originating from tUe catalytic pUase. More specifically, as tUe particle size decreases, tUe electron density of the catalytic phase becomes less bound and the resulting wavefunctions become spatially more extended and more likely to overlap witU wavefunctions of tUe support matrix. Due to size considerations, tUe catalytic pUase of tUe instant materials includes metal or metal alloy particles Uaving a size of 100 A or less. More preferably, the catalytic phase includes metal or metal alloy particles having a size of 50 A or less. Most preferably, the catalytic phase includes metal or metal alloy particles having a size of 20 A or less.
A second factor contributing to the extent and nature of wavefunction overlap is the relative orientation of the interacting wavefunctions of the catalytic phase and support matrix. Wavefunctions are typically spatially non-isottopic and have characteristic directionaUty and reflect asymmetries of electron density in bonding and anti-bonding molecular orbitals. Even if wavefunctions show great spatial extent, the regions of space occupied by the wavefunctions of the catalytic pUase and support matrix must be co-extensive in order to create spatial overlap and to produce the electronic interaction of the instant invention. The requirement for spatial co-extensiveness is tantamount to a directionality or wavefunction orientation requirement.
A tUird factor contributing to the extent and nature of wavefunction overlap is the relative energy of the interacting wavefunctions of the catalytic phase and support matrix. It is known from quantum mechanics that the relative energies of wavefunctions having adequate spatial extent and suitable orientation influences the strength of interaction between the wavefunctions and the resulting effect on electron density. The closer in energy tUe interacting wavefunctions are, tUe stronger is tUeir strengtU of interaction. Wavefunctions Uaving identical or similar energies sUow stronger interactions tUan wavefunctions Uaving dissimilar energies. A stronger electronic interaction between wavefunctions indicates a greater degree of mixing of wavefunctions from the catalytic phase and the support matrix to provide a new wavefunction that better reflects a combination of the properties of the catalytic phase and support matrix. As the mismatch in energy between contributing wavefunctions increases, mixing may still occur, but the resulting wavefunctions exhibit characteristics that are predominantly controlled by the wavefunctions of one of the catalytic phase or support matrix.
A fourth factor contributing to the extent and nature of wavefunction overlap is the relative phases of the interacting wavefunctions of the catalytic phase and support matrix. The wavefunction phase can be positive or negative and the relative phases of the wavefunctions of the catalytic phase and support matrix dictates whether the electronic interaction is of the bonding type or anti-bonding type.
Wavefunctions having the same phase interact to provide a new wavefunction of the bonding type and result in a bonding-type electronic interaction between the catalytic phase and support matrix of the instant invention. Wavefunctions having opposite phase interact to provide a new wavefunction of the anti-bonding type and result in an anti-bonding type electronic interaction between the catalytic phase and support matrix of the instant invention.
In addition to electronic interactions of the bonding and anti-bonding types, the electronic interaction of the instant materials also includes interactions of the donor-acceptor type. A donor-acceptor interaction is an interaction between orbitals or wavefunctions of the catalytic phase and support matrix in which at least one of the interacting wavefunctions is unoccupied or only partly occupied and not fully occupied. A donor-acceptor interaction is one in which electron density is transferred from the donor to the acceptor where the acceptor receives the transferred electron density in a partially occupied or unoccupied orbital. In the instant invention, either the catalytic phase or the support matrix may perform as the donor or acceptor. If the catalytic phase functions as the donor, the donor-acceptor interaction leads to a net reduction of electron density in the vicinity of the surface of the catalytic phase and the catalytic properties are accordingly altered. Conversely, if the catalytic phase functions as the acceptor, the donor-acceptor interaction leads to a net increase of electron density in the vicinity of the surface of the catalytic phase.
Through the principles of wavefunction overlap, the instant invention provides supported catalytic materials exhibiting an electronic interaction between the catalytic phase and the electronically active support matrix. As described hereinabove, the electronic interaction may be of the bonding, anti-bonding or donor-acceptor type and is manifest in an alteration of the total electron density and/or distribution thereof in the vicinity of the surface or catalytic sites of the particles of the catalytic phase. The alteration is relative to and represents a deviation of the electron density and/or distribution thereof in the vicinity of the surface or catalytic sites of the particles of the catalytic phase when equivalently dispersed on an inert support matrix. The instant electronic interaction is a mutual interaction between the catalytic phase and support matrix and results from the fact that the support matrix provides for more than mere physical dispersion and mechanical support of the catalytic phase.
A schematic depiction of tUe structure and electronic interaction provided by the instant supported catalytic materials is provided in Figs. 5A - 5C. Fig. 5 A shows a depiction of a conventional supported catalytic material. The conventional supported catalyst includes a particle of a catalytic phase 100 supported by an inert support 200. The electron density present at or near the surface of the catalytic particle 100 is denoted by Q. Figs. 5B and 5C show depictions of different embodiments of supported catalytic materials according to the instant invention. The material depicted in Fig. 5B includes the particle of the catalytic phase 100 (same particle as shown in Fig. 5 A) supported by the electronically active support matrix 300. The electronically active support matrix 300, through wavefunction overlap as described hereinabove, provides a net transfer of electron density to or near the surface of the 5. catalytic particle 100. The direction of transfer of electron density is depicted by the arrow. As a result of the wavefunction overlap, the electron density at or near the surface of the catalytic particle 100 has increased to Q + Δ where Δ represents the perturbation of electron density at or near the surface of the catalytic particle 100 due to the electronic interaction with the support matrix 300. TUe material depicted in Fig. 5C includes tUe particle of tUe catalytic pUase 100 (same particle as sUown in Fig. 5 A) 0 supported by the electronically active support matrix 400. The electronically active support matrix 400, through wavefunction overlap as described hereinabove, induces a net transfer of electron density from the catalytic particle to the support matrix 400. The direction of transfer of electron density is depicted by the arrow. As a result of the wavefunction overlap, the election density at or near the surface of the catalytic particle 100 has decreased to Q - Δ where Δ represents the perturbation of electron density at 5 or near the surface of the catalytic particle 100 due to the electronic interaction with the support matrix 400. The strength of the electronic interaction between the catalytic phase and the electronically active support matrix determines the magnitude of the perturbation Δ in the embodiments shown in Figs. 5B and 5C. A strong electronic interaction reflects significant wavefunction overlap and leads to a greater perturbation Δ. A weak electronic interaction reflects insignificant wavefunction overlap and leads to a 0 lesser perturbation Δ.
The magnitude of the perturbation of electron density Δ may vary for different particles of a catalytic phase in the instant electronically active supported catalytic materials. Factors that influence Δ include particle size, particle orientation, particle composition, interparticle separation, and support matrix composition. In embodiments of the instant invention having a distribution of particles sizes for 5 the catalytic phase or a pluraUty of chemically or physically distinct attachment sites on the support matrix for the particles, it is expected that a distribution or range of values of Δ will exist.
Perturbations in the electron density at or near the surface of the catalytic phase are not limited solely to perturbations in the magnitude of electron density, but also extend to perturbations in the spatial distribution of electron density at or near the surface of the catalytic phase. In the presence of an 0 inert support matrix, the electron density at or near the surface of a catalytic particle is distributed in a particular, usually inhomogeneous fashion. The electronic interaction of the instant invention may perturb this spatial distribution and may induce a rearrangement, repositioning or otherwise cause a redistribution of electron density at or near the surface of a catalytic particle.
The perturbed electron density and/or spatial distribution thereof leads to modification of the 5 catalytic properties of the catalytic phase. The instant electronic interaction has the effect of extending the catalytically active portion of the instant supported materials beyond the physical boundaries of the catalytic phase. The delocaUzation of electron density from tUe catalytic pUase to tUe support matrix, for example, Uas tUe effect of enlarging the physical region that influences catalytic behavior to include portions of the support matrix. Rather than being defined solely by the intrinsic catalytic properties and 0 physical dispersion of the catalytic phase on the support matrix, the instant materials provide for further control and modification of catalytic properties through an electronic interaction mechanism whose origins arise from wavefunction overlap.
One or more catalytic properties pertaining to the performance of supported catalytic materials may be improved through the electronic interaction of the instant materials. These catalytic properties include reaction rate, overall catalytic activity, selectivity, range of catalytically affected reactants, and the range of environmental conditions under which catalytic effects are observed. Overall catalytic activity refers to the rate of reaction and/or the conversion efficiency of a catalyst. Selectivity refers to the ability of a catalyst to discriminate among potential reactants wben in tUe presence of a pluraUty of reactants. Oftentimes a catalytic reaction is preferentially completed on a particular component witUin a mixture of components. Range of catalytically affected reactants refers to tUe range of cUemical species tUat undergo a catalyzed reaction in tUe presence of a catalyst. Catalysis of a particular species may become possible through the electronic interaction of the instant materials where said species was not catalyzed by the same catalytic phase supported by an inert support matrix or in the absence of the electronic interaction of the instant catalytic materials. The range of environmental conditions refers to external conditions such as temperature, pressure, concentration, pH, etc. under which a particular catalytic reaction may occur. The electronic interaction of the instant supported catalyst may facilitate catalytic function at conditions tUat are more convenient tUan tliose for tUe corresponding reaction in tUe presence of a conventional supported catalyst sUowing no electronic interaction. TUe reaction temperature, for example, may be lowered tUrougU use of the instant catalytic materials. Similarly, the catalytic activity at a particular temperature may be greater for a particular reaction through use of the instant electronically active supported catalytic material. Of particular note in the context of the instant invention is tUe possibility of inducing a catalytic effect in a catalytic phase where said catalytic phase exhibits no catalytic activity with respect to a particular reaction or process at a particular set of conditions. Electrochemical, chemical, thermal, bond cleavage, bond formation, rearrangements, isomerizations and other types of reactions are within the scope of the instant invention.
As indicated hereinabove, the catalytic phase of the instant supported materials are preferably metals or metal alloys in the form of particles. More preferably, the catalytic particles comprise a transition metal and most preferably the catalytic particles comprise Ni. Transition metals are preferred because their valence electronic structure includes d-orbitals. As previously described by the instant inventor, d-orbitals provide for chemical modification effects through the concept of total interactive environment that lead to novel electronic environments in hydrogen storage materials. Further discussion of the concepts of chemical modification and total interactive environment may be found in the co-pending parent appUcation (U.S. Pat. Appl. Ser. No. 10/405,008) as well as in U.S. Patent Nos. 4,431,561; 4,623,597; 5,840,440; 5,536,591; 4,177,473; and 4,177,474 of wUicU tUe instant inventor is a co-inventor; tUe disclosures of wUicU are Uerein incorporated by reference. In tbe instant invention, the concept of total interactive environment is extended to supported catalytic materials t rougU tUe electronic interaction between the catalytic phase and support matrix due to wavefunction overlap as described hereinabove. d-orbitals facilitate wavefunction overlap because tbey are generally spatially well extended and are capable of Uybridizing in many ways to achieve a variety of different spatial orientations. Transition metals thereby faciUtate tUe estabUsUment, activation or inducement of the electronic interaction of the instant materials.
In a typical embodiment of the instant invention, the catalytic particles have a non-uniform particle size distribution and are randomly dispersed spatially on the electronically active support matrix. The range of particle sizes depends on the composition of the catalytic phase as well as the method of preparing and/or dispersing the catalytic particles. Different particle sizes are expected to experience different perturbations in the magnitude and/or spatial distribution of electron density at or near the surface of a catalytic particle. A range of perturbations is thus expected for catalytic phases comprising a plurality of catalytic particles tUat includes a plurality of particle sizes. Dispersion of tUe catalytic particles refers generally to tUe spatial distribution of tbe catalytic particles on tUe support matrix.

TUe support matrix of tUe instant materials is typically an oxide material. Transition metal oxides (e.g. zirconia, titania), lantUanide oxides (e.g. yttria) and main group oxides (e.g. alumina, silica) are preferred support matrices. Treatment of tUe surface of tUe instant support materials (tUrougU e.g. etching or passivation) may facilitate tUe development of electronic interactions between tbe support materials and a supported catalytic pUase.
TUe electronic interaction of tUe instant supported catalytic materials originates from wavefunction overlap between the catalytic phase and the support matrix. The participating wavefunctions may be derived from orbitals that are unoccupied, partially filled or filled and still lead to modification of the electron density at or near the surface of the catalytic phase as described hereinabove. The modification of the electron density of the catalytic phase may result in a modification of existing or intrinsic catalytic properties of a catalytic phase (i.e. modification of those catalytic properties of the catalytic phase when unsupported or supported on an inert support matrix) or may result in the estabUsUment of catalytic activity with respect to a particular reaction at a particular set of conditions wUere no corresponding activity exists for tUe catalytic pUase when unsupported or supported on an inert support matrix.
EXAMPLE 5
An embodiment of a catalyst according to the instant invention is now described. In this example, a supported catalytic material that includes a catalytic phase comprising nickel or nickel alloy particles dispersed on an oxidized metal alloy support is described. The materials of this example are formed from metal alloys represented by the AB, AB2, AB5 or A2B families of Uydrogen storage materials where component A is a transition metal, rare earth element or combination thereof and component B is a transition metal element, Al or combination thereof. Representative examples of component A include La, Ce, Pr, Nd, and combinations thereof including mischmetal. Representative examples of component B include Ni, Co, Mn, Al and combinations thereof.
Representative hydrogen storage catalysts having catalytic properties in accordance with the instant invention are disclosed in the parent U.S. Pat. Appl. Ser. No. 10/405,008. For the purposes of this example, we consider catalysis associated with the electrochemical hydrogen storage process. An electrochemical hydrogen storage material produces hydrogen from water through a catalyzed electrochemical reaction and stores the hydrogen for later retrieval. In the retrieval process, stored hydrogen is removed from storage sites and catalytically reacted with hydroxyl ions to form water.

During charging of an electrochemical hydrogen storage alloy, a current is provided to the hydrogen storage alloy in the presence of water to form a metal hydride and hydroxyl ions. The alloy is formally reduced in the charging process. The discharging of a metal hydride involves the oxidation of the metal hydride in the presence of hydroxyl ions to form a metal or metal alloy and water. Electrons are produced during discharging to form a current. The charging and discharging processes are catalyzed. The alloys of this example were prepared by combining mischmetal and other components in elemental form (purity of each element > 99%) in the required stoichiometric ratio in an MgO crucible. The mischmetal used in this example included La, Ce, Pr, and Nd in a molar ratio of La:Ce:Pr:Nd = 10.5:4.3:0.5: 1.4. The total mass of the combined starting elements was approximately 2 kg. The crucible was subsequently placed into a water-cooled induction furnace under a 1 atm. argon atmosphere, heated to about 1350 °C and held at that temperature for 15-20 minutes. During heating, the material in the crucible melted and became superheated to provide better homogeneity. After this heating step, the material was cooled down to just slightly above its melting point (ca. 1280 °C) and immediately poured into a steel mold through a tundish. After pouring, the material was cooled to room temperature. The resulting ingot was then annealed at 950 °C for 8 hours in a vacuum chamber pumped by a diffusion pump. After anneaUng, the ingot was returned to room temperature. The cooled ingot was then mechanically pulverized and sieved through a 200 mesh filter. The material was further activated to modify surface oxides that form during preparation and improve catalytic performance. Activation is a process in which the surface oxide layer of a hydrogen storage alloy is removed, reduced or modified to improve performance. The process of activation may be accomplished, for example, by etching, electrical forming, pre-conditioning or other methods suitable for removing or altering excess oxides or hydroxides. See, for example, U.S. Pat. No. 4,717,088; the disclosure of which is hereby incorporated by reference.
The activation process faciUtates a preferential corrosion of tUe surface oxide layer to form a porous support matrix witU catalytic particles attacUed tliereto. The catalytic particles have sizes on the order of tens of angstroms and include one or more transition metals. The support matiix is a metal, metal oxide or combination thereof in which the oxidic content may be varied by varying activation conditions. While not wishing to be bound by theory, the instant inventors speculate that as the activation conditions become more extreme and/or activation time becomes sufficiently long, the oxidic content of the support matrix decreases as a preferential corrosion effect converts a greater fraction of the support matrix to the metallic state to form catalytic particles. As corrosion progresses, the support matrix becomes more porous as described in the co-pending parent U.S. Appl. Ser. No. 10/405,008 and in the context of the instant invention, the support matrix is believed by the instant inventors to become more electronically active. As discussed in the co-pending parent U.S. Appl. Ser. No. 10/405,008, preferential corrosion may be faciUtated tUrougU tUe inclusion of a microstructure modifying element in the hydrogen storage alloy composition and/or through control of alloy processing conditions.
In this example, the catalytic properties of hydrogen storage alloys in accordance with tUe instant invention are examined in a low temperature discUarge context and compared to a conventional catalytic material lacking an electronic interaction between tUe catalytic particles and support matrix.

More specifically, the specific power of different batteries that include a different hydrogen storage alloy as the negative electrode material was determined at -30 °C. Three UHP C-cell batteries were constructed and tested at -30 °C in an HEV power test. Each C-cell included a nickel hydroxide positive electrode, a separator, a KOH electrolyte and a compacted negative electrode that included a hydrogen storage alloy. One battery included the Bl hydrogen storage alloy
(Lai05Ce43Pr05Ndι ^NiM 5C050Mn46A160Cu34), a second battery included the B 12 hydrogen storage alloy (Laio 5Ce43Pr0 sNdi 4Ni645Co3 0Mn46A160Cu54), and a third battery included the B hydrogen storage alloy (Laι05Ce 3Pr05Ndi 4Ni600C0127Mn5.9Al47) where the B 1 and B 12 alloys are alloys having catalytic properties according to the instant invention and the B alloy is a conventional alloy that does not benefit from the electronic interaction associated with the materials of the instant invention. The catalytic phase of all three hydrogen storage materials includes catalytic particles comprising nickel or a nickel alloy. The intrinsic catalytic activity of the catalytic particles of the three alloys is expected to be similar. The batteries of this example exemplify NiMH (nickel metal Uydride) batteries and are generally representative of recbargeable batteries.
The specific power of each battery was determined in an HEV power test at -30 °C and various states of charge. The HEV power test procedure is discussed in the co-pending parent U.S. Appl. Ser. No. 10/405,008 and the specific power was calculated as the product (%V0C) ΛImlΑ). Since greater catalytic activity leads to higher specific power, the specific power is used in this example as a measure of the catalytic activity of the three hydrogen storage alloys. Except for the hydrogen storage alloy, the components and configuration of the three batteries were identical.
The specific power at a time delay of 6 sec following initiation of a 10 sec 10C discharge pulse of the battery at -30 °C and different states of charge was determined for each of the three batteries at different states of charge (100%, 80%, and 50%). At 100% state of charge, the specific powers of the batteries were determined to be: 260 W/kg (B12), 240 W/kg (Bl) and 210 W/kg (B). At 80% state of charge, the specific powers of the batteries were determined to be: 210 W/kg (B 12), 170 W/kg (Bl) and 100 W/kg (B). At 50% state of charge, the specific powers of the batteries were determined to be: 150 W/kg (B12), 105 W/kg (Bl) and essentially zero for the B alloy.
The specific power results show that batteries including the two alloys according to the instant invention (B12 and Bl) exhibited significantly higher specific powers at all tested states of charge at -30°C than the battery that included the conventional alloy (B). The higher specific powers observed for the B 12 and Bl batteries indicate greater catalytic activity and demonstrate a beneficial catalytic effect arising from the electronic interaction described hereinabove for supported catalytic materials according to the instant invention. This example additionally illustrates that supported catalytic materials according to the instant invention provide catalytic activity at conditions at which a conventional supported catalytic material shows no catalytic activity. The electronic interaction present in the Bl and B 12 alloys in this example provides for catalytic activity upon discharge at conditions of 50% state of charge and -30 °C, while no catalytic activity was observed in the conventional alloy under the same conditions. Similar degrees of improvement for batteries based on the Bl and B 12 alloys relative to a battery based on the B alloy were also observed at room temperature (20 °C) and at 0 °C.

The disclosure and discussion set forth herein is illustrative and not intended to Umit the practice of the instant invention. Numerous equivalents and foreseeable variations thereof are envisioned to be within the scope of the instant invention. It is the following claims, including all equivalents, in combination with the foregoing disclosure, which define the scope of the instant invention.