U.S. patent application number 10/623939 was filed with the patent office on 2004-10-07 for supported catalyst having electronic interaction between catalytic phase and support matrix.
Invention is credited to Ovshinsky, Stanford R..
Application Number | 20040198597 10/623939 |
Document ID | / |
Family ID | 33097011 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040198597 |
Kind Code |
A1 |
Ovshinsky, Stanford R. |
October 7, 2004 |
Supported catalyst having electronic interaction between catalytic
phase and support matrix
Abstract
A catalyst including a catalytic phase supported by an
electronically active support matrix. An electronic interaction
that occurs between the catalytic phase and support matrix leads to
perturbations in the magnitude and/or spatial distribution of
electron density at or near the surface of the catalytic phase. The
electronic interaction originates from an overlap of wavefunctions
associated with electron density of the catalytic phase with
wavefunctions associated with electron density of the catalytic
phase. Embodiments include those in which the electronic
interaction is of the bonding-type, anti-bonding type or donor
acceptor type. Filled, partially filled or unoccupied orbital
states may participate in the electronic interaction. The
perturbation in electron density induced by the electronic
interaction modifies the catalytic properties of the catalytic
phase.
Inventors: |
Ovshinsky, Stanford R.;
(Bloomfield Hills, MI) |
Correspondence
Address: |
ENERGY CONVERSION DEVICES, INC.
2956 WATERVIEW DRIVE
ROCHESTER HILLS
MI
48309
US
|
Family ID: |
33097011 |
Appl. No.: |
10/623939 |
Filed: |
July 18, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10623939 |
Jul 18, 2003 |
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10405008 |
Apr 1, 2003 |
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Current U.S.
Class: |
502/337 |
Current CPC
Class: |
H01M 4/383 20130101;
H01M 10/345 20130101; Y02E 60/32 20130101; Y10S 420/90 20130101;
Y02E 60/10 20130101 |
Class at
Publication: |
502/337 |
International
Class: |
B01J 023/755 |
Claims
We claim:
1. A catalytic material comprising: a catalytic phase comprising
particles of a catalytic material, said catalytic particles having
a size distribution and an electronically active support matrix,
said electronically active support matrix mechanically supporting
said catalytic phase, said catalytic phase being dispersed in a
spatial distribution on said electronically active support matrix;
wherein said electronically active support matrix interacts
electronically with said catalytic phase, said electronic
interaction originating from wavefunction overlap between said
catalytic phase and said electronically active support matrix, said
electronic interaction modifying a catalytic property of said
catalytic phase relative to said catalytic property of said
catalytic phase when supported on an inert support matrix.
2. The catalytic material of claim 1, wherein said catalytic phase
comprises a transition metal.
3. The catalytic material of claim 1, wherein said catalytic phase
comprises nickel.
4. The catalytic material of claim 1, wherein said electronically
active support matrix comprises a metal oxide.
5. The catalytic material of claim 1, wherein said electronically
active support matrix comprises a metal.
6. The catalytic material of claim 1, wherein said electronic
interaction is a bonding type interaction.
7. The catalytic material of claim 1, wherein said electronic
interaction is an anti-bonding type interaction.
8. The catalytic material of claim 1, wherein said electronic
interaction is a donor-acceptor type interaction.
9. The catalytic material of claim 1, wherein said electronic
interaction induces a perturbation in the magnitude or spatial
distribution of electron density at or near the surface of said
catalytic phase.
10. The catalytic material of claim 1, wherein said electronic
interaction causes delocalization of electron density from said
catalytic phase to said electronically active support matrix.
11. The catalytic material of claim 1, wherein said catalytic phase
is non-catalytic when supported on said inert support matrix.
12. The catalytic material of claim 1, wherein said modified
catalytic property of said catalytic phase supported on said
electronically active support matrix is relative to said catalytic
phase having said particle size distribution and dispersed in said
spatial distribution when supported on said inert support
matrix.
13. The catalytic material of claim 1, wherein said catalytic
property is a chemical reaction rate.
14. The catalytic material of claim 1, wherein said catalytic
property is selectivity.
15. The catalytic material of claim 1, wherein said modified
catalytic property provides a faster chemical reaction rate at
temperatures of 20.degree. C. or below.
16. The catalytic material of claim 1, wherein said catalytic
material is included in a rechargeable battery and said modified
catalytic properties provide faster discharge rates of said
rechargeable battery.
17. The catalytic material of claim 16, wherein said rechargeable
battery is a nickel metal hydride battery.
Description
RELATED APPLICATION INFORMATION
[0001] This application is a continuation in part of U.S.
application Ser. No. 10/405,008 filed on Apr. 1, 2003 and entitled
"Hydrogen Storage Alloys Having A High Porosity Surface Layer"; the
disclosure of which is herein incorporated by reference.
FIELD OF INVENTION
[0002] This invention pertains generally to catalytic materials
that include a catalytic phase supported on a support matrix. More
particularly, this invention pertains to catalytic materials in
which supported metal particles interact electronically with a
support to provide novel catalytic properties. Most particularly,
this invention pertains to customization of catalytic function
through the engineering of wavefunction overlap between metal
particles and a surrounding support matrix.
BACKGROUND OF THE INVENTION
[0003] Chemical reactions underlie many technological and
industrial processes and new advances in technology and in
mankind's standard of living oftentimes are directly attributable
to the discovery of new chemical reactions or improvements in
existing chemical reactions. The range of applications that benefit
from chemical reactions include pharmaceuticals, petrochemicals,
plastics, lubricants, textiles and microelectronics. Scientists
continually search for new reactions capable of producing new
materials and products in new ways.
[0004] The feasibility of a particular chemical reaction depends on
thermodynamic and kinetic factors. Thermodynamics dictates whether
a chemical reaction occurs spontaneously or not. According to
thermodynamics, spontaneous chemical reactions are those that
exhibit a negative Gibbs energy change. Spontaneous chemical
reactions are preferred for applications because they are more
energy efficient and generally more cost effective than
non-spontaneous reactions. Even if a reaction occurs spontaneously,
it may still be impractical if it occurs at an insufficient rate.
Reaction kinetics govern the rate at which chemical reaction
occurs.
[0005] The rate of a chemical reaction typically controls whether a
particular reaction is practical or not and 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.
A catalyst increases the rate of reaction by providing an
alternative, lower energy pathway or mechanism for accomplishing
the reaction. Catalysts may be solids liquids or gases and catalyst
selection is oftentimes optimized empirically for particular
reactions. Identification of an effective catalyst for a particular
reaction is frequently not obvious from a simple consideration of
the reactant and products involved in the reaction. Instead,
detailed experimentation involving a number of potential catalyst
materials is normally required for the identification of a suitable
catalyst for a particular reaction.
[0006] 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
[0007] The instant invention 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 metallic or
oxide support matrix.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1. Schematic depictions of a catalytic phase supported
by a support matrix.
DETAILED DESCRIPTION OF THE INVENTION
[0009] Conventional supported catalysts have been widely used to
promote a variety of chemical reactions. Conventional supported
catalysts include a dispersed catalytic phase that is supported on
a support matrix. The role of the support matrix is to provide
mechanical 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 the catalytic properties of the catalytic
phase. The support matrix of a conventional supported catalyst is
thus referred to herein as an inert or electronically inert support
matrix.
[0010] The catalytic phase of conventional supported catalysts is
typically comprised of particles of a catalytic material. The
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.
[0011] 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 the support matrix provides more than simple
mechanical 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.
[0012] 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.
[0013] 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, thereby
providing unorthodox structure, bonding and catalytic sites. In
addition to surface area and intrinsic catalytic activity, the size
of the catalytic particles in the context of the instant invention
further influences the tendency of the catalytic phase to interact
electronically with a support matrix. As used herein, 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 the catalytic phase to the
support matrix or from the support matrix to the catalytic phase or
mutual transfer or delocalization 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 the spatial
extent of electron density of the catalytic phase 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 with the electronic
interaction of the instant materials distinguishes the interaction
of the catalytic phase and the support from the Coulombic type
electrostatic interaction that may be present in conventional
supported catalysts. Whereas a Coulombic type interaction is
physical in nature, delocalization or localization of electron
density is chemical in nature.
[0014] While not wishing to be bound by theory, the instant
inventor believes that the 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 stabilize a collection
of atoms. The 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 underlies the stability of materials.
[0015] In quantum mechanical 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 delocalize is related to the spatial
extent of the 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
localized 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 with or overlap wavefunctions of neighboring
atoms. Electron density described by spatially extended
wavefunctions is thus more likely to delocalize than electron
density described by tightly bound wavefunctions.
[0016] 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:
1s<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 localize or delocalize through
interactions with neighboring atoms than are lower energy
electrons.
[0017] The 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.
[0018] 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 delocalizes from one or both of the catalytic phase and
support matrix.
[0019] 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 the 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.
[0020] 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 the region between
the interacting entities 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 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. In 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.
[0021] The catalytic properties of the catalytic phase 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
ability of catalytic particles to attract and stabilize one or more
reactant species for a period of time sufficient to permit a
chemical reaction or molecular rearrangement to occur. The electron
density at or near the surface of the catalytic particles
influences the strength 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.
[0022] 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 delocalization of
electron density away from the 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 the vicinity of the
surface of a catalytic particle and may result in an increase in
electron density at or near the surface of the catalytic particles.
By modifying the electron density at or near the surface of
catalytic particles, the electronic interaction resulting from the
wavefunction overlap present between the catalytic particles and
support matrix of the instant materials provides a mechanism for
modifying the catalytic properties of the catalytic phase and the
supported material in general.
[0023] The strength and type (bonding vs. anti-bonding) of the
electronic interaction in the instant supported catalytic materials
ultimately depends on the extent and nature of wavefunction overlap
between the catalytic phase and electronically active support
matrix. The extent and nature of overlap depend on several factors.
First, the spatial extent of the wavefunctions associated with the
electron density of the catalytic phase and support matrix
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 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 with each other or
other wavefunctions and consequently show little tendency to
provide the electronic interaction underlying the enhanced
catalytic properties of the instant invention.
[0024] Catalytic phases or support matrices whose wavefunctions
extend beyond the physical 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.
[0025] 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 the
catalytic phase and/or support matrix. Greater Lewis base strength
of a catalytic phase and/or support matrix composition, increases
the likelihood of spatial overlap of wavefunctions and of achieving
the electronic interaction of the instant invention.
[0026] The size of the particles of a catalytic phase also
influences the spatial extent of the wavefunctions originating from
the catalytic phase. More specifically, as the particle size
decreases, the electron density of the catalytic phase becomes less
bound and the resulting wavefunctions become spatially more
extended and more likely to overlap with wavefunctions of the
support matrix. Due to size considerations, the catalytic phase of
the instant materials includes metal or metal alloy particles
having a size of 100 .ANG. or less. More preferably, the catalytic
phase includes metal or metal alloy particles having a size of 50
.ANG. or less. Most preferably, the catalytic phase includes metal
or metal alloy particles having a size of 20 .ANG. or less.
[0027] 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-isotropic and have
characteristic directionality 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 phase 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.
[0028] A third 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 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 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] A schematic depiction of the structure and electronic
interaction provided by the instant supported catalytic materials
is provided in FIGS. 1A-1C. FIG. 1A 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. 1B and 1C show depictions of different embodiments of
supported catalytic materials according to the instant invention.
The material depicted in FIG. 1B includes the particle of the
catalytic phase 100 (same particle as shown in FIG. 1A) 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 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+.DELTA. where .DELTA. 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. The
material depicted in FIG. 1C includes the particle of the catalytic
phase 100 (same particle as shown in FIG. 1A) 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 electron density at or near the
surface of the catalytic particle 100 has decreased to Q-.DELTA.
where .DELTA. 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 400. The strength of
the electronic interaction between the catalytic phase and the
electronically active support matrix determines the magnitude of
the perturbation .DELTA. in the embodiments shown in FIGS. 1B and
1C. A strong electronic interaction reflects significant
wavefunction overlap and leads to a greater perturbation .DELTA.. A
weak electronic interaction reflects insignificant wavefunction
overlap and leads to a lesser perturbation .DELTA..
[0033] The magnitude of the perturbation of electron density
.DELTA. may vary for different particles of a catalytic phase in
the instant electronically active supported catalytic materials.
Factors that influence .DELTA. 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 the catalytic phase or
a plurality 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 .DELTA. will exist.
[0034] 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 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.
[0035] The perturbed electron density and/or spatial distribution
thereof leads to modification of the 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 delocalization of electron density from the catalytic
phase to the support matrix, for example, has the 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 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.
[0036] 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 when in the presence of a plurality of
reactants. Oftentimes a catalytic reaction is preferentially
completed on a particular component within a mixture of components.
Range of catalytically affected reactants refers to the range of
chemical species that undergo a catalyzed reaction in the 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 that are more
convenient than those for the corresponding reaction in the
presence of a conventional supported catalyst showing no electronic
interaction. The reaction temperature, for example, may be lowered
through 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 the 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.
[0037] 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 cop rise 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 application (U.S. patent application
Ser. No. 10/405,008) as well as in U.S. Pat. Nos. 4,431,561;
4,623,597; 5,840,440; 5,536,591; 4,177,473, and 4,177,474 of which
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 they are generally spatially well extended and are capable
of hybridizing in many ways to achieve a variety of different
spatial orientations. Transition metals thereby facilitate the
establishment, activation or inducement of the electronic
interaction of the instant materials.
[0038] 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 that includes a plurality of
particle sizes. Dispersion of the catalytic particles refers
generally to the spatial distribution of the catalytic particles on
the support matrix.
[0039] The support matrix of the instant materials is typically an
oxide material. Transition metal oxides (e.g. zirconia, titania),
lanthamide oxides (e.g. yttria) and main group oxides (e.g.
alumina, silica) are preferred support matrices. Treatment of the
surface of the instant support materials (through e.g. etching or
passivation) may facilitate the development of electronic
interactions between the support materials and a supported
catalytic phase.
[0040] The electronic interaction of the 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 establishment of catalytic activity with respect to a
particular reaction at a particular set of conditions where no
corresponding activity exists for the catalytic phase when
unsupported or supported on an inert support matrix.
EXAMPLE
[0041] 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, AB.sub.2, AB.sub.5 or A.sub.2B
families of hydrogen 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.
[0042] Representative hydrogen storage catalysts having catalytic
properties in accordance with the instant invention are disclosed
in the parent U.S. patent application 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.
[0043] 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.degree. 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.degree. 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.degree. C. for 8 hours in a vacuum chamber pumped by a
diffusion pump. After annealing, 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.
[0044] The activation process facilitates a preferential corrosion
of the surface oxide layer to form a porous support matrix with
catalytic particles attached thereto. The catalytic particles have
sizes on the order of tens of angstroms and include one or more
transition metals. The support matrix 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.
application 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. application Ser. No. 10/405,008,
preferential corrosion may be facilitated through the inclusion of
a microstructure modifying element in the hydrogen storage alloy
composition and/or through control of alloy processing
conditions.
[0045] In this example, the catalytic properties of hydrogen
storage alloys in accordance with the instant invention are
examined in a low temperature discharge context and compared to a
conventional catalytic material lacking an electronic interaction
between the 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.degree. C. Three UHP
C-cell batteries were constructed and tested at -30.degree. 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 B1 hydrogen storage alloy
(La.sub.10.5Ce.sub.4.3Pr.sub.0.5Nd.sub.1.4N-
i.sub.64.5CO.sub.5.0Mn.sub.4.6Al.sub.6.0Cu.sub.3.4), a second
battery included the B12 hydrogen storage alloy
(La.sub.10.5Ce.sub.4.3Pr.sub.0.5N-
d.sub.1.4Ni.sub.64.5Co.sub.3.0Mn.sub.4.6Al.sub.6.0Cu.sub.5.4), and
a third battery included the B hydrogen storage alloy
(La.sub.10.5Ce.sub.4.3Pr.su-
b.0.5Nd.sub.1.4Ni.sub.60.0Co.sub.12.7Mn.sub.5.9Al.sub.4.7) where
the B1 and B12 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 hydride) batteries and are
generally representative of rechargeable batteries.
[0046] The specific power of each battery was determined in an HEV
power test at -30.degree. C. and various states of charge. The HEV
power test procedure is discussed in the co-pending parent U.S.
application Ser. No. 10/405,008 and the specific power was
calculated as the product ({fraction (2/3)} V.sub.oc.sup.)
(1/3I.sub.max). 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.
[0047] The specific power at a time delay of 6 sec following
initiation of a 10 sec 10C discharge pulse of the battery at
-30.degree. 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 (B 1) and
210 W/kg (B). At 80% state of charge, the specific powers of the
batteries were determined to be: 210 W/kg (B12), 170 W/kg (B1) and
100 W/kg (B). At 50% state of charge, the specific powers of the
batteries were determined to be: 150 W/kg (B12)1-105 W/kg (B1) and
essentially zero for the B alloy.
[0048] The specific power results show that batteries including the
two alloys according to the instant invention (B12 and B1)
exhibited significantly higher specific powers at all tested states
of charge at -30.degree. C. than the battery that included the
conventional alloy (B). The higher specific powers observed for the
B12 and B1 batteries indicate greater catalytic activity and
demonstrate a beneficial catalytic effect rising 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 B1 and B12 alloys in this example provides for catalytic
activity upon discharge at conditions of 50% state of charge and
-30.degree. C., while no catalytic activity was observed in the
conventional alloy under the same conditions. Similar degrees of
improvement for batteries based on the B1 and B12 alloys relative
to a battery based on the B alloy were also observed at room
temperature (20.degree. C.) and at 0.degree. C.
[0049] The disclosure and discussion set forth herein is
illustrative and not intended to limit 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.
* * * * *