Note: Descriptions are shown in the official language in which they were submitted.
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NEW TYPE OF CATALYTIC MATERIALS BASED ON ACTIVE METAL-
HYDROGEN-ELECTRONEGATIVE ELEMENT COMPLEXES INVOLVING
HYDROGEN TRANSFER
Field of the Invention
The invention relates to new catalytic materials of specific composition and
molecular structure, which are able to catalyze and improve efficiency of
chemical
reactions involving hydrogen transfer.
Background of the Invention
Many chemical reactions in both inorganic and organic chemistry involve
relocation of hydrogen atoms, ions (protons), or molecules, which need to be
transferred from one chemical molecule to another molecule, or exchanged with
other atoms, ions or radicals in the reaction route. Amongst many such
reactions, the
most common types are: hydrogenation and dehydrogenation, reduction/oxidation,
various types of reactions involving organic compounds, electrochemical
reactions,
and reactions in~ all types of fuel cells. All these reactions may exhibit a
wide
spectrum of various types of chemical bonding and various underlying atomic-
scale
mechanisms, as well as different nature of atomic interactions. In all of
them, there is
however one universal feature that controls the rate and efficiency of these
reactions, i.e. the effectiveness of hydrogen relocation. In the course of
these
reactions, the events of hydrogen transfer or exchange occur repeatedly and
improving the efficiency of hydrogen relocation is the main challenge for many
chemical technologies. In the most effective way, the reactions with hydrogen
transfer can be facilitated by catalysis. The ultimate role of catalysts is to
promote
atomic-scale processes of hydrogen transfer or exchange (by lowering the
activation
energy connected with hydrogen relocation). In most cases, in the absence of
the
catalysts the chemical reaction would either not occur at all, or would take
place with
much lower efficiencies, rates, or at higher temperatures. The general field
of
catalysis (which became one of the critical factors for the chemical
technologies) is
at present relatively wide and well developed, with a large number of various
catalytic materials being investigated and used.
In general, there are two main categories of catalysts: heterogeneous and
homogeneous. Homogeneous catalysts are in the same phase as the basic
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reactants, and heterogeneous catalysts are in the different phase, for
example: solid
catalysts in the gaseous reactions. The development and current understanding
of
catalysis allows us to distinguish two essential catalytic mechanisms, i.e.
acidic
catalysis and basic catalysis, where reactants act either as bases toward
catalysts
which in turn act as acids, or as acids toward basic catalysts. Amongst many
types
of basic catalysts, the following are the most common: (H. Hattori
"Heterogeneous
Basic Catalysts", Chem. Rev. 1995, 95, 537)
Single component metal oxides (e.g. alkaline earth oxides)
Zeolites
Supported alkali metal ions (e.g. alkali metals on alumina)
Clay minerals
Non-oxide catalysts (e.g. KF supported on alumina)
For acidic catalysis, the following catalytic materials are being commonly
used
(A. Corma "Inorganic Solid Acids and Their Use in Acid-Catalyzed Hydrocarbon
reactions", Chem. Rev. 1995, 95, 559):
Solid acid catalysts (e.g. amorphous silica-alumina and aluminum phosphate)
Zeolites and zeotypes
Heteropoly acids
Sulfated metal oxides.
The simplest catalysts are single-phase materials, such as metals, oxides,
sulfides, carbides, borides and nitrides. Metal particles are among the most
important catalysts, being used on a large scale for refining petroleum,
conversion of
automobile exhaust, hydrogenation of carbon monoxide, hydrogenation of fats
and
many other processes. Multiphase catalysts usually consist of an active phase
(e.g.
metal particles or clusters) dispersed on a carrier (support). It is generally
assumed
that metal particles act most probably as active centers for the hydrogen
dissociation, but the role of the support is so far still not fully
understood. In practice
the metal is often expensive (for example Pt) and may constitute only about 1
wt.%
of the catalytic material, being applied in a finely dispersed form as
particles on a~
high-area porous metal oxide support (B.C.Gates "Supported Metal Clusters:
Synthesis, Structure, and Catalysis", Chem. Rev. 1995, 95, 511 ). Supported
metal
clusters are synthesized through organometallic chemistry on surfaces, gas-
phase
cluster chemistry and special preparation of zeolite cages. The preparation
methods
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commonly use techniques from preparative chemistry, such as precipitation,
hydrolysis, and thermal decomposition. These processes involve mixing of
solutions,
blending of solids, filtration, drying, calcinations, granulation, extrusion
(J.E. Schwarz
et al. "Methods of Preparation of Catalytic Materials" Chem. Rev. 1995, 95
477).
Although, generally, catalysis is one of the most important fields of chemical
technology, it is still far from being accomplished. Most catalysts are
difficult to
fabricate and the production process involves a sequence of several, complex
steps
(as mentioned above), many of which are still not completely understood (J.E.
Schwarz et al. "Methods of Preparation of Catalytic Materials" Chem. Rev.
1995, 95
477). As a result, subtle changes in the preparative details may result in
dramatic
alteration in the properties of the final catalysts, which may thus become
ineffective.
Especially, the manner in which the active component of the catalyst is
introduced
onto a support, as well as the nature of the interaction between the active
element
and the carrier, could be of critical importance. Another crucial challenge in
the
preparation of catalysts is the ability to prepare these materials with
sufficiently high
surface area. Also, most of the multicomponent metal oxides require high-
temperature treatment (exceeding 1000°C, as for alumina-based oxides),
which is a
significant technical drawback.
Another problem is that catalytic materials usually require "activation" i.e.
some special treatment, before they could become active as catalysts, for
example
high-temperature annealing in vacuum or hydrogen atmosphere. Even then,
however, in certain cases, the effect of annealing in hydrogen can indeed
improve
the catalyst's activity, but for other catalytic materials, the same treatment
can
actually have an adversary effect. Although the experimental data suggest that
different catalytic supports lead to different effects of hydrogen treatment,
these
problems are still unresolved (B.C. Gates "Supported Metal Clusters:
Synthesis,
Structure, and Catalysis", Chem. Rev. 1995, 95, 511 ). Moreover, most
catalysts
become rapidly deactivated when exposed to air. They should be therefore
handled
under protective atmosphere, and pretreated at high temperatures after
exposures to
air in order to regain their catalytic properties.
All the above disadvantages of conventional catalytic materials cause
continuous efforts to develop new, inexpensive materials with catalytic
properties
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suitable for reactions involving hydrogen transfer, and to develop novel
methods of
their preparation.
The invention presents a practical and cost-efficient solution to this
problem,
by introducing a new type of catalytic materials, their manufacture and use as
catalysts in chemical reactions.
Summary of the Invention
In one broad aspect, the present invention provides a composition of matter
prepared in accordance with a method comprising the steps of:
(a) combining a substance selected from the group consisting of: metal or
metalloid, or an alloy thereof, or a compound thereof, or an homogeneous or
inhomogeneous combination of at least two of the metal or metalloid, the alloy
thereof, or the compound thereof, with a source of hydrogen, to form a first
intermediate;
(b) milling the first intermediate to form a second intermediate;
(c) combining the second intermediate with a source of an electronegative
element, to form a third intermediate; and
(d) milling the third intermediate.
In yet another broad aspect, the present invention provides a composition of
matter prepared in accordance with a method comprising:
(a) combining a hydrogenated, metal or metalloid, or an alloy thereof, or a
compound thereof, or an homogeneous or inhomogeneous combination of at least
two of the hydrogenated, metal or metalloid, or the alloy thereof, or the
compound
thereof, with a source of an electronegative element, to form a first
intermediate; and
(b) milling the first intermediate.
In one aspect, each of the milling steps is conducted in a substantially inert
gaseous environment.
In another aspect, where an oxidative environment is preferably avoided in
the milling step, the milling step is carried out in a gaseous environment
having an
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insufficient concentration of an oxidizing agent to effect deleterious
oxidation of the
metal or metalloid component, or the alloy thereof, or the homogeneous or
inhomogeneous combination of at least two of the metal or metalloid.
In yet another aspect, where a reducing environment is preferably avoided in
the milling step, the milling step is carried out in a gaseous environment
having an
a insufficient concentration of a reducing agent to effect deleterious
reduction of the
intermediate product.
In another aspect, the metal or metalloid is selected from the group
consisting
of Li, Na, K, Be, Mg, Ca, Y, Sc, Ti, Zr, Hf, V, Nb, Ta, Pt, Pd, Ru, Rh, Ge,
Ga, In, La,
Ce, Pr, Nd, Dy, AI, Si, B, Cr, Mo, W, Mn, Fe, Co, Ir, Ni, Cu, Ag, Au, Zn, Sn,
Pb, Sb,
and Bi .
In a further aspect, the electronegative element is selected from the group
consisting of O, F, N, CI, S, P, C, Te, and I.
In yet a further aspect, the compositions have a particulate form consisting
of
a plurality of particles, and having a particle size of less than 100 microns.
In even a
further aspect, 80% of the particles have a particle size of less than 50
microns, and
. the grains present in the particles are characterized by a size less than
100 nm.
In another aspect, the composition has an X-ray diffraction pattern that
exhibits a characteristic Bragg's reflection of a co-ordination of (i) metal
or metalloid
and (ii) hydrogen.
In yet another aspect, the milling imparts an impact energy sufficient to
effect
the formation of the new atomic co-ordinations. In this respect, the milling
can be
carried out in a high energy ball mill.
The present invention also provides, in another broad aspect, a composition of
matter prepared in accordance with a method comprising the steps of:
(a) effecting a reaction between (i) a metallic substance selected from the
group consisting of a metal or metalloid, or an alloy thereof, or a
compound thereof, or an homogeneous or inhomogeneous combination of
at least two of the metal or metalloid, or the alloy thereof, or the compound
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thereof, and (ii) hydrogen, by a first milling, to form an intermediate
product; and
(b) effecting a reaction between the intermediate product and an
electronegative element, by a second milling.
Additionally, in yet another broad aspect, the present invention provides a
composition of matter prepared in accordance with a method comprising
effecting
reaction between (i) a metallic substance selected from the group consisting
of:
hydrogenated, metal or metalloid, or an alloy thereof, or a compound thereof,
or an
homogeneous on inhomogeneous combination of at least two of the hydrogenated,
metal or metalloid, ~ or the alloy thereof, or the compound thereof, and (ii)
an
electronegative element, by milling.
Each of the above enumerated compositions of matter can function as hydrogen
transfer facilitators. In this respect, each of the above-enumerated
compositions can
combine with metallic substance selected from the group consisting of: (a) a
hydride
of a metal or metalloid, or an alloy thereof, or a compound thereof, or a
homogeneous or inhomogeneous combination of at least two of the metal or
metalloid, the alloy thereof, or the compound thereof, or (b) a metal or
metalloid
capable of absorbing hydrogen to form a hydride, or an alloy thereof, or a
compound
thereof, or an homogeneous or inhomogeneous combination of at least two of the
metal or metalloid, the alloy thereof, or the compound thereof, such combining
effecting sufficient contact between the hydrogen transfer facilitator and the
second
metallic substance so that the hydrogen transfer facilitator is configured to
effect
absorption or desorption of hydrogen by the second metallic substance.
In one aspect, the hydrogen transfer facilitator is mechanically alloyed to
the
second metallic substance. Such mechanical alloying can be effected by
milling.
By functioning as a hydrogen transfer facilitator, the ' above-described
compositions can effect a process of hydrogenating and dehydrogenating a
hydrogen storage composition comprising the steps of:
(a) effecting absorption of hydrogen by the hydrogen storage composition; and
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(b) effecting desorption of the absorbed hydrogen from the hydrogen storage
composition; wherein steps (a) and (b) are carried out in any order.
In another broad aspect, the present invention provides a hydrogen storage
composition comprising:
a metallic substance selected from the group consisting of: (a) a hydride of a
metal
or metalloid, or an alloy thereof, or a compound thereof, or a homogeneous or
inhomogeneous combination of at least two of the metal or metalloid, the alloy
thereof, or the compound thereof, or (b) a metal or metalloid capable of
absorbing
hydrogen to form a hydride, or an alloy thereof, or a compound thereof, or an
homogeneous or inhomogeneous combination of at least two of the metal or
metalloid, the alloy thereof, or the compound thereof; and
a hydrogen transfer facilitator having an atomic co-ordination characterized
by one of
the following structural formula:
(a) (M+M1 )-H--E
or
(b) (M)-H--E
wherein the hydrogen transfer facilitator is disposed in sufficient contact
with the
metallic substance so that the hydrogen transfer facilitator is configured to
effect
absorption or desorption of hydrogen by the second metallic substance.
The hydrogen transfer facilitator can also have other atomic co-ordinations,
including:
(1) M--H-E; or
(2) M-H--H.
Brief Description of the Drawings
The invention will be better understood and objects other than those set forth
above will become apparent when consideration is given to the following
detailed
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description thereof. Such description makes reference to the annexed drawings
wherein:
Figure 1 illustrates x-ray diffraction patterns referred toI in Example 1 of a
Ti-
based catalyst ntion and that of comparative materials;
Figure 2 illustrates x-ray diffraction patterns referred to in Example 1 of
comparative materials to the Ti-based catalyst ;
Figure 3 illustrates hydrogen absorption referred to in Example 1 of a Ti/Ti-
based catalyst system;
Figure 4 illustrates hydrogen absorption referred to in Example 1 of a Ti/Ti-
based catalyst system and that of comparative materials;
Figure 5 illustrates hydrogen absorption referred to in Example 1 of
comparative materials to the Ti/Ti-based catalyst system;
Figure 6 illustrates x-ray diffraction patterns referred to in Example 1 of a
hydrogenated TilTi-based catalyst system and that of comparative materials;
Figure 7 illustrates x-ray diffraction patterns referred to in Example 2 of Zr-
based catalysts and that of comparative materials;
Figure 8 illustrates x-ray diffraction patterns referred to in Example 2 of
Zr/Zr-
based catalyst systems and that of comparative materials, before and after
hydrogenation;
Figure 9 illustrates hydrogen absorption referred to in Example 2 of Zr/Zr-
based catalyst systems and that of comparative materials;
Figure 10 illustrates hydrogen absorption referred to in Example 2 of a Zr/Zr-
based catalyst system under different hydrogen pressures;
Figure 11 illustrates hydrogen absorption referred to in Examples 2 and 3 of
various Zr/Zr-based catalyst systems;
Figure 12 illustrates x-ray diffraction patterns referred to in Example 3 of
Zr/Cu0 based catalysts and that of comparative materials;
Figure 13 illustrates x-ray diffraction patterns referred to in Example 3 of
Ti/Cu0 based catalysts and that of comparative materials;
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Figure 14 illustrates x-ray diffraction patterns referred to in Example 3 of
Zr/Fe0 based catalysts and that of comparative materials;
Figure 15 illustrates x-ray diffraction patterns referred to in Example 3 of
various Ti/metal oxide based catalysts;
Figure 16 illustrates x-ray diffraction patterns referred to in Example 7 of
Zr/V
based catalysts and that of comparative materials;
Figure 17 illustrates x-ray diffraction patterns referred to in Example 4 of
Cu0
based catalysts and that of comparative materials;
Figure 18 illustrates x-ray diffraction patterns referred to in Example 3 of
Mg-
based system before and after hydrogenation; .
Figure 19 illustrates hydrogen absorption referred to in Examples 3 of Mg-
based system;
Figure 20 illustrates hydrogen absorption referred to in Examples 5 of LiAIH4-
based system;
Figure 21 illustrates hydrogen desorption referred to in Examples 6 of
NaAIH4-based system;
Figures 22 and 23 illustrate dehydrogenation kinetics referred to in Example 6
of NaAIH4-based system; and
Figure 24 illustrates hydrogen desorption referred to in Examples 6 of
NaAIH4-based system.
Detailed Description
The present invention relates to a composition of matter characterized by a
particular atomic configuration. The composition of matter is useful for
effecting
improved hydrogen transfer kinetics in various kinds of chemical, reactions
which
depend on the efficiency of hydrogen relocation or exchange. In this respect,
such
composition of matter of the present invention can be described as a "hydrogen
transfer facilitator". Where this composition of matter is not consumed in
these
chemical reactions, the hydrogen transfer facilitator can also be described as
a
catalyst. Examples of such reactions whose reaction kinetics may be improved
by
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this hydrogen transfer facilitator include: (i) hydrogenation and
dehydrogenation of a
wide spectrum of compounds, including simple and complex metal ,hydrides,
hydrocarbons and various organic compounds, reforming of hydrocarbons,
alcohols,
polymerization, cracking and hydrolysis, (ii) electrochemical reactions,
including
anodic and cathodic reactions, and electrolysis of water and salts, (iii)
reactions in
fuel cells, and (iv) reduction/oxidation reactions.
Although not wishing to be bound by theory, it is believed that the ability of
the
composition of matter of the subject invention to effect improved hydrogen
transfer
kinetics is attributable to the fact that the hydrogen transfer facilitator is
characterized-
by at least one kind of specific atomic co-ordination. Again, not wishing to
be bound
by theory, it is believed that at least one of these specific kinds of subject
atomic co-
ordination can be described in accordance with the following structural
formula:
(1 ) (M+M1 )-H--E
wherein:
M is a metal or metalloid, or an alloy thereof, or a compound thereof, or a
homogeneous or inhomogeneous combination of at least two of the metal or
metalloid, or the alloy thereof, or the compound thereof. Examples of suitable
metals
and metalloids include: Li, Na, K, Be, Mg, Ca, Y, Sc, Ti, Zr, Hf, V, Nb, Ta,
Pt, Pd, Ru,
Rh, Ge, Ga, In, La, Ce, Pr, Nd, Dy, AI, Si, and B.
M1 is an optional other metal, or an alloy thereof, or a compound thereof, or
a
homogeneous or inhomogeneous combination of at least two of the metal, or the
alloy thereof, or the compound thereof. Examples of suitable metals include:
Cr,
Mo, W, Mn, Fe, Co, Ir, Ni, Cu, Ag, Au, Zn, Sn, Pb, Sb, and Bi.
H is hydrogen
E is an electronegative element, such as O, F, N, CI, S, P, C, Te, I, Br, and
compounds thereof. Examples of suitable compounds include oxides, nitrides,
halides, sulphides, tellurides, phosphides, including mixed compounds, such as
CO
and NO. Other suitable compounds of the enumerated electronegative elements
include those co-ordinated with hydrogen atoms, such as water, hydroxides,
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phenols, alcohols, salts, acids, alkoxides, thiolS, organic acids, salts of
organic acids,
acid amides, amines, acid halides, alkyl halides, sulphones, and
organometallics;
and wherein hydrogen bonding exists between H and E.
Once again, and not wishing to be bound by theory, it is also believed that
the
hydrogen transfer facilitator has two further atomic co-ordinations which
effects
improved hydrogen transfer, and that such atomic co-ordinations can be
described in
accordance with the following structural formulae:
(2) M__H_E
(3) M-H--H
wherein M, H, and E~ have the same meanings as in (1), and wherein in (2),
hydrogen bonding exists between M and H, and wherein in (3), hydrogen bonding
exists between H and H.
These types of atomic co-ordinations are generally recognized and described
by L. Bramer, "Direct and Indirect Roles of Metal Centres in Hydrogen
Bonding", eds.
J.A.K. Howard, F.H. Allen and G.P. Shields; NATO ASI Series E: Applied
Sciences
1999, 360, 197-210, Kluwer Academic Publishers, Dordecht, Netherlands.
The composition of matter of the present invention can be made by, firstly,
combining (i) a metallic substance selected from the group consisting of: a
metal or
metalloid, or an alloy thereof, or a compound thereof, or an homogeneous or
inhomogeneous combination of at least two of the metal or metalloid, or the
alloy
thereof, or the compound thereof, with (ii) a source of hydrogen, to form a
first
intermediate. The first intermediate is then milled to effect reaction between
the
metallic substance and the hydrogen. As a result of the reaction, the hydrogen
becomes bonded to the metallic substance as a second intermediate. The second
intermediate is then combined with a source of an electronegative element.
Such
combination is then milled to effect reaction between the second intermediate
and
the electronegative element to form the resultant composition.
Examples of suitable metallic substance, and electronegative elements and
their sources, are described above.
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The milling operations must be able to impart sufficient impact energy to
effect
the reaction between hydrogen and the metallic substance, as well as the
reactiori
involving the electronegative component. In this respect, in one embodiment, a
mechanical grinding or milling can be carried out in a high energy ball mill.
Suitable
ball mills include tumbler ball mills, planetary ball mills, and attrition
ball mills. The
mechanical treatment imparted by such milling operations provides enhanced
reactivity of the reagents, by means of the continuous creation of fresh
surfaces
unaffected by oxides and hydroxides, and introduces local stress and
deformation
which is believed to enhance the rate of reaction.
Preferably, each of the above described reactions is preferably carried out in
a substantially inert gaseous environment in order for the desired reaction
between
the metallic substance and hydrogen to take place. In this respect, the
reaction
between the metal substance and hydrogen is preferably carried out in a
gaseous
environment having an insufficient concentration of an oxidizing agent to
effect
deleterious oxidation of the metallic substance. The presence of the oxidizing
agent
interferes with the reaction between the metallic substance and hydrogen.
Deleterious oxidation of the metallic substance occurs when the metallic
substance
reacts to an unacceptable degree with an oxidizing agen (eg. oxygen) so as to
significantly interfere with reactivity of~ the metallic substance with
hydrogen.
Unacceptable degree of reaction varies depending on the circumstance. ~ In the
context of hydrogen storage compositions, oxidation becomes unacceptable where
the resultant composition does not possess sufficient catalytic activity to
justify the
space it is occupying. Similarly, the reaction between the metallic substance-
hydrogen intermediate with the electronegative element is preferably be
carried out
in a gaseous environment having an insufficient concentration of a reducing
agent to
effect deleterious reduction of the subject intermediate product. Such
reducing
agent would otherwise interfere with the reaction between the electronegative
element and the intermediate. Deleterious reduction of the metallic substance
occurs when the metal-hydrogen co-ordination of a reactive intermediate (a
precursor to the hydrogen transfer facilitator) reacts to an unacceptable
degree with
a reducing agent so as to significantly interfere with the reactivity between
the
intermediate and the electronegative element. In the context of hydrogen
storage
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compositions, reduction becomes unacceptable where the resultant composition
does not possess sufficient catalytic activity to justify the space it is
occupying.
The composition of matter may also be prepared from a hydrogenated
metallic substance. Hydrogenated metallic substances can be directly reacted
with
the electronegative element to form the composition of matter of the subject
invention without having to first undergo a reaction with hydrogen. In this
respect,
the present invention also provides a composition of matter prepared in
accordance
with a method comprising: (a) combining a hydrogenated metallic substance with
a
source of an electronegative element, to form a firsfi intermediate; and (b)
milling the
first intermediate to effect reaction between (i) the hydrogenated metallic,
and (ii) fihe
electronegative component.
In one embodiment, the composition of matter may be prepared by milling the
metallic substance with a liquid, such as water or an alcohol or mixtures
thereof. In
this respect, the present invention further provides a composition of matter
prepared
in accordance with a method comprising: (a) combining a metal or metalloid, or
an
alloy thereof, or a compound thereof, or an homogeneous or inhomogeneous
combination of at least to the metal or metalloid, or the alloy thereof, or
the
compound thereof, with the liquid selected from the group consisting of water
and
alcohols and mixtures thereof, to form a first intermediate, and (b) milling
the first
intermediate. Preferably, excess of liquids relative to metal substances
should be
avoided. This is because excess liquids could interfere with reaction
mechanisms
between the metallic substance and hydrogen, thereby leading to a reduction of
the
catalytic capability of the ultimately-formed composition of matter (hydrogen
transfer
facilitator). In this respect, preferably, the molar ratio of the ,liquid to
the metallic
substance is less than 1:1.
The hydrogen transfer facilitator may also be formed by contacting the
metallic substance with gaseous reagents to effect the necessary
transformations
which form the desired atomic co-ordination. In this respect, the solid
metallic
component can be exposed to hydrogen and oxygen (or chlorine, or fluorine, or
nitrogen) in the gas phase. However, instead of applying the gas mixture, a
sequence of gas admission steps is applied. The process involves, for example,
exposure to hydrogen under certain conditions of temperature and pressure,
which
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results in hydrogen adsorption or absorption, through the metal surface. It is
then
followed by the admission of the other gas under certain conditions of
temperature
and pressure. In order to finally form the required atomic configuration
according to
the invention, either complete oxidation or complete reduction of the metallic
component should be avoided in the process, in order for both basic components
(hydrogen and the electronegative element) to be present in the.metallic
complex.
In order to improve and control the reactivity of the metallic component and
the efficiency of the formation of the catalytic complexes, this solid-gas
reaction is
performed preferably in a ball mill. In this process, the milling of the
metallic powder
proceeds consecutively under the atmosphere of hydrogen, followed by ball
milling
under oxygen (or chlorine, or other gases), performed in a precisely defined
sequence of conditions. As indicated above, instead of a metallic component,
an
already hydrogenated metallic component can be used as a starting material, or
even a. previously formed hydride (or a mixture of hydrides).
The hydrogen transfer facilitator may even further be formed by contacting the
metallic substance with solid reagents to effect the necessary transformations
which
form the desired atomic co-ordination.ln this case, at least one of the
components
among hydrogen and the electronegative element is introduced in the form of a
solid
compound, for example a solid hydrocarbon, such as solid polymer, or oxide,
chloride, fluoride, ~ sulfide, carbide, telluride or iodide, alkoxide etc.
Hydrides,
hydroxides, solid acids, bases, or other compounds can be also used as
hydrogen-
and electronegative element- sources. These compounds can also contain metals
or
metalloids either different or the same as the main (M + M1) components. As
above,
the most effective way of producing the required catalytic complexes is to use
a high-
energy ball mill, providing a solid-state reaction between the metallic
element (either
previously hydrogenated or not) and the solid source of the electronegative
element
and hydrogen. The hydrogen source (for example a solid hydrocarbon, a hydride)
can be at first introduced to the metallic element. Subsequently, a source of
an
electronegative element is added in a second stage, for example, an oxide. In
a one-
stage process, a specific combination of solid carriers supplying the hydrogen
and/or
the electronegative element can be used, for example a mixture of an oxide and
a
hydride, a mixture of alkoxides, oxides, chlorides, etc. A specific example of
the
process in the solid state is when a solidified source of hydrogen and of the
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electronegative element is introduced, for example water in the form of ice,
which
can also be performed at adequately low temperatures.
All the above-described methods can be used in various combinations,
depending on the specific formula of the catalytic complex. For example, solid
hydride can be milled under gaseous oxygen, liquid fluoride can be milled with
a
hydrogenated metallic alloy, or gaseous hydrogenation can be performed in a
ball
mill, then followed by ball milling with water, or with a solid hydrocarbon.
The compositions of matter of the present invention, which function as
hydrogen transfer facilitators, are preferably in particulate form, having a
particle size
less than 100 microns, and also being characterized by the fact that 80% of
the
particles have a particle size less than 50 microns. Preferably, the particles
possess
nanocrystalline characteristics, such that the grain size of the particles is
less than
100nm.
As mentioned above, the composition of matter of the present invention can
be used as a hydrogen transfer facilitator for effecting the hydrogenation and
dehydrogenation of a metal hydride or hydrogenation of unsaturated organic
compounds.
To effectively function as a hydrogen transfer facilitator for improving the
kinetics of hydrogenation and dehydrogenation in the context of hydrogen
storage
materials, the hydrogen facilitator must be integrated, or intermixed, with
the
substance being hydrogenated and dehydrogenated. In this respect, a hydrogen
storage composition of the present invention can be prepared by combining the
hydrogen transfer facilitator, as described above, to a metallic substance
selected
from the group consisting of (a) a hydride of a metal or metalloid, or an
alloy thereof,
or a compound thereof, or a homogeneous or inhomogeneous combination of at
least two of the metal or metalloid, the alloy thereof, or the compound
thereof, or (b)
a metal or metalloid capable of absorbing hydrogen to form a hydride, or an
alloy
thereof, or an homogeneous or inhomogeneous combination of at least two of the
metal or metalloid, or the alloy thereof, or the compound thereof, such
combining
effecting sufficient contact between the hydrogen transfer facilitator and the
second
metallic substance so that the hydrogen transfer facilitator is configured to
effect
absorption or desorption of hydrogen by the metallic substance, The hydrogen
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transfer facilitator can be combined with the metallic substance by way of
mechanical alloying through ball milling. Relative to the intensity of
milling, required
to effect formation of the hydrogen transfer facilitator catalyst, lower
milling intensity
may be used for intermixing of the hydrogen transfer facilitator and the
metallic
substance. The hydrogen transfer facilitator can also be intermixed with the
metal
hydride or hydridable metal using other methods such as mixing, spraying,
deposition, condensation, compaction, sintering, and co-sintering.
Once combined with the metal hydride or hydridable metal, the hydrogen
transfer facilitator can enhance the kinetics of hydrogen and dehydrogenation
of the
hydrogen storage composition. Hydrogenation is the process whereby hydrogen is
absorbed by the hydrogen storage composition. Hydrogenation is not intended to
indicate that complete hydrogenation of the hydrogen storage composition has
necessarily occurred, and contemplates both a complete hydrogenation and a
partial
hydrogenation resulting from the absorption of hydrogen by the hydrogen
storage
composition. Similarly, dehydrogenation is not intended to indicate that
complete
dehydrogenation has necessarily occurred, and contemplates both a complete
dehydrogenation and a partial dehydrogenation resulting from the desorption of
at
least a part of the hydrogen content of the hydrogen storage composition.
Absorption of hydrogen by the metallic substance refers to the association of
hydrogen with a metallic substance. Also mechanisms for association include
dissolution, covalent bonding, or ionic bonding. Dissolution describes a
process
where hydrogen atoms is incorporated in the voids of a lattice structure of a
metal or
intermetallic alloy. Examples of such metal hydrides include vanadium
hydrides,
titanium hydrides and hydrides of vanadium-titanium alloys. An example of a
covalently bonded hydride is magnesium hydride. Example of ionically bonded
hydrides are sodium hydride and lithium hydride.
In the process of the catalyst preparation it is preferable to precisely
control
the electronegative element contribution, both in the way of its introduction
and in the
amount. One method of controlling the exact amount of the electronegative
element
in the preparation process is to use additional components that have the
ability to
either provide the electronegative element (e.g. being oxygen donors through
their
in-situ reduction) or eliminate the excess of the electronegative element
(through in-
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situ oxidation which prohibits detrimental oxidation of the metallic
component). As
shown in the examples, such oxygen-donating components could be, for example,
copper oxide (which becomes reduced to copper during the process of the
catalyst
preparation) or zinc or aluminum (which become oxidized when necessary,
instead
of the destructive oxidation of the main metallic component).
The present invention will be described in further detail with reference to
the
following non-limitative examples.
EXAMPLES
Example 1 ~ Ti-based Catalyst Prepared by Reaction with Methanol
A Ti-based catalyst was produced both from titanium powder and titanium
hydride. Both methods gave equally good catalytic capability of the resulting
catalyst
so long as deleterious oxidation of titanium was prevented. .
Commercial titanium hydride (TiH2) was used as a starting material,, and was
purchased from Aldrich (purity 98%, powder -32'5 mesh). X-ray diffraction
pattern of
this hydride was created using a Bruker D8 Discover X-ray diffraction system
(as
was the case for all X-ray diffraction results discussed herein) and is shown
in
Fig.1 a. The X-ray diffraction pattern exhibits a characteristic set of
Bragg's
reflections consistent with the International Centre for Diffraction Data
database
PDF-2, card number 65-0934.
One gram of titanium hydride was loaded into a stainless steel vial together
with approximately 1 ml of methanol (methyl alcohol HPLC grade 99.9%) and
stainless steel balls, giving a' ball-to-powder ratio of about 16:1 on a
weight basis.
The loading was done in a glove box with protective argon atmosphere (less
than I
ppm of oxygen and less than 1 ppm of water). Subsequently, the vial was
mounted
in a high-energy ball mill (SPEX CentriPrep 8000M Mixer/Mill). This milling
device
provides violent and complex movements in three mutually perpendicular
directions,
with frequency of about 1200 cycles/minute. Ball milling was performed for 9
hours,
with particular care about perfect sealing of the vial. After the process, the
material
turned into deep-black, very fine powder, without visual presence of the
liquid phase.
Instead, a significant weight increase of the powder was observed, of the
order
significantly exceeding any possible contamination from the vial. Fig.1 b
shows x-ray
diffraction pattern of the resulting powder (i.e. the "new catalyst"). The
pattern shows
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no apparent transformation of the basic crystallographic structure of the
hydride (all
Bragg's reflections remain at similar 28 positions as those characteristic for
the
original hydride structure). Also, no additional phase can be seen in the
diffraction
pattern (no additional Bragg's reflections). In particular, none of the
normally
expected reaction products, namely oxide phase or alkoxide phase, appeared to
be
present.
In Figs. 1c and 1d, x-ray diffraction patterns for commercial Ti0 (purchased
from Alfa Aesar, purity 99.5%, -325 mesh powder) and for titanium methoxide
Ti(OCH3)4 (CH30H)X (purchased from Alfa Aesar, purity 95% powder) are given
for
comparison. By comparison, the only apparent difference in the x-ray
diffraction
pattern of the new catalyst is a significant widening of the Bragg's
reflections, which
is usually interpreted as a result of increased level of strain, defects, and
formation of
the nanocrystalline structure. These are all common features, often seen in
ball
milled materials. .
X-ray diffraction data for the new Ti-based catalyst was compared to that of
materials comprising similar elements, with a view to understanding the
structure
and co-ordination of the Ti-based catalyst. The following comparative
materials were
prepared: TiH2 ball milled without any additions, ball milled TiO, a mixture
of TiH2
and Ti0 ball milled without additions, the same mixture of TiH2 and Ti0 but
ball
milled with methanol, and Ti milled with excess of water and under oxygen-
containing atmosphere. All these materials were prepared under identical ball
milling
conditions as for the formation of the Ti-based catalyst, with the same
parameters as
above, and using the same technique of loading and handling. Fig. 2
illustrates x-ray
diffraction patterns of these , materials, of which only one - dry TiH2 -- has
x-ray .
diffraction pattern similar to the new catalyst, proving that, indeed, the
local
crystallographic arrangement of our catalyst preserves the required Ti-H
coordination
similar to that in the TiH2.
Catalytic properties of the above Ti-based catalyst was assessed with respect
to the hydrogenation of titanium, i.e. in the process of formation of titanium
hydride.
According to "Compilation of IEA/DOE/SNL Hydride Databases" by G. Sandrock and
G. Thomas http://hydpark ca sandia.aov, titanium hydride can be formed by
direct
reaction with H2 gas, but "must be heated to 400 - 600°C to activate"
and can be
"easily deactivated by impurities such as 02 and H20".
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The Ti-based catalyst was next incorporated or bonded with titanium powder,
to assess hydrogen absorption kinetics. Titanium powder was purcnasea trom
Hira
Aesar, with 99.5% purity, -325 mesh powder. Titanium powder was mixed with 10
wt.% of the new Ti-based catalyst (prepared as above) and ball milled for a
short
period of time (less than 1 hour) in order to provide good distribution of the
catalyst
over titanium powder.
Hydrogen absorption capabilities of the material (and all other materials
herein) were measured in an automated, computer controlled gas titration
system,
which allows precise evaluation of hydrogen uptake and release by measuring
pressure changes in a closed system.
In contrast to conventional titanium which requires high-temperature
activation, titanium powder catalyzed by the new .titanium-based catalyst
exhibited
very fast (within about 20 seconds) formation ~ of titanium hydride at room
temperature, without any activation or preheating, as shown in Fig.3. The
hydrogen
pressure used for hydrogenation was relatively very low, less than 1 bar, and
decreased to about 0.4 bars due to hydrogen consumption during absorption. In
a
parallel experiment at room temperature, hydrogen pressure used for absorption
was
as low as 300 mbars, and the formation of titanium hydride occurred within
less than
30 minutes, as shown in Fig.3b, again without any activation or preheating.
In comparative experiments, a first sample of titanium powder was subject to
short ball milling (1 hour) with no additions, and a second sample of titanium
powder
was intermixed by short ball milling (I hour) with additions of the before-
mentioned
comparative materials (dry, ball milled TiH2, ball milled TiO, a mixture of
TiH2 and
Ti0 ball milled without additions, the same mixture of TiH2 and Ti0 but ball
milled
with methanol, and Ti milled with excess of water and under oxygen-containing
atmosphere). These additions were introduced to the titanium powder by using
the
same procedure as used for the new Ti-based catalyst, and were subsequently
exposed to about 1 bar of hydrogen pressure in the gas titration system. As
shown
in Figs. 4 and 5, neither titanium alone, nor with any of the above additions,
showed
measurable hydrogen absorption within the period of time required by the Ti-
based
catalyst system to be fully charged.
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Fig. 6 shows x-ray diffraction patterns which confirm the hydrogenation
measurements of Ti in the Ti-systems studied above. Fig. 1 a illustrates x-ray
diffraction pattern of the initial Ti powder (consistent with the
International Centre for
Diffraction Data database PDF-2, card number 89-5009). Figs. 6b and 6d
illustrate
x-ray diffraction patterns for (i) Ti intermixed (by using short ball milling
,described
above) with dry, ball milled TiH2 after hydrogenation (Fig. 6b), and (ii) Ti
intermixed
(by using short ball milling described above) with the new catalyst (Fig. 6d).
Although no apparent differences can be seen between these two materials in
their
initial state before hydrogenation, there was a fundamental difference in
their
hydrogenation behaviour. While dry TiH2 was inactive as a catalytic addition
(and
titanium powder remained unchanged after hydrogenation attempts as shown in
pattern 6c), the new catalyst, formed in the manner described above, caused
full
transformation of titanium into titanium hydride, as shown in diffraction
pattern in
Fig. 6e. Commercial TiH2 pattern is shown in Fig. 6f for comparison.
These particular results (i.e. the exceptional catalytic ability of the new Ti-
based catalyst, as compared for example with dry TiH2) oppose common
understanding of the activation of titanium system (as for example in the
Sandrock's
Hydride Database, where "the presence of 02 or H20 should deactivate titanium
at
low temperature"). The new catalyst (which is not only assumed to contain
oxygen,
but, in some embodiments, is produced using water, or water-alcohol mixtures)
not
only does not deactivate titanium but instead causes exceptional kinetics for
titanium
hydrogenation without any activation and at room temperature under very low
hydrogen pressures.
Example 2: A Zr -Based Catalyst
Zirconium-based catalysts according to the invention can be produced from
both zirconium and zirconium hydride. In general, it involves formation of the
Zr - H
atomic configuration, complemented by introduction of the electronegative
element.
For example, the electronegative element can be derived from a liquid such as
water
or alcohol, or from, for example, metal oxides. Similar to the above examples
using
titanium, a variety of processes can be effectively applied in the preparation
of the
Zr-based catalysts.
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In the current example, zirconium powder was purchased from Alfa Aesar
(with purity 95+%, average powder size 2-3micron, packaged in water). The
disadvantage of metallic zirconium is that it is very sensitive to oxidation.
Since
normally zirconium does not react with water, packaging in water is the most
common method of protecting Zr from deterioration in air. Although in some
cases
water can be used as a reagent in the process of preparation of Zr-based
catalyst,
dried zirconium was always used as a starting material in order to fully
control the
amount of water added. The first step of the experiment was to dry commercial
zirconium powder overnight under vacuum, with continuous pumping. Fig. 7a
shows
x-ray diffraction pattern of the dried commercial zirconium powder. The
structure of
Zr is reflected in its characteristic set of Bragg's reflections, which is
consistent with
the International Centre for Diffraction Data database PDF-2, card number 89-
4892.
Prepared zirconium powder was subsequently used as starting material for the
formation of new Zr-based catalysts, which involved ball milling of Zr with'
water or
alcohol, and also with metal oxides or metals. In order to differentiate the
processes
according to the invention from the effects of ball milling only, Zr powder
alone was
subjected to ball milling under similar conditions as in the catalyst
preparation
experiments (described below). As seen in Fig. 7b, which shows x-ray
diffraction
pattern of the ball-milled zirconium, the effects of ball milling are limited
to the usual
features of Bragg's reflection broadening, caused by introduction of stress,
defects
and nanocrystalline structure.
800 mg of dried zirconium powder was loaded into a stainless steel vial
together with approximately 0.35 ml of methanol (methyl alcohol HPLC grade
99.9%)
and stainless steel balls, giving a ball-to-powder ratio of about 20:1 on a
weight
basis. The loading was done in a glove box with protective argon atmosphere
(less
than 1 ppm of oxygen and less than 1 ppm of water), with particular care about
perfect sealing of the vial. Subsequently, the vial was mounted in a high-
energy ball
mill (SPEX CentriPrep 8000M Mixer/Mill). Ball milling was performed for 9
hours.
After the process, there was no visual presence of the liquid phase, and the
product
was a black, very fine powder. A significant weight increase of the powder was
observed. Fig.7c shows x-ray diffraction pattern of the resulting material
(i.e. the new
Zr-based catalyst). The pattern clearly shows a crystallographic structure
different
from that of zirconium (Figs. 7a and 7b) and can be interpreted as a zirconium
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hydride crystallographic configuration, since all Bragg's reflections occur at
similar 28
positions as those characteristics for the zirconium hydride structure, in
accordance
with the International Centre for Diffraction Data database PDF-2, card number
65-
0745. A very similar pattern (although with relatively sharper Bragg's
reflections, as
shown in Fig. 7d) was obtained in another experiment, where zirconium hydride
ZrH2
was used as a starting material instead of zirconium metal (ZrH2 was purchased
from
Alfa Aesar, purity 99.7%, <10 micron powder). All experimental conditions and
details in this were similar to those used for zirconium metal, as described
above.
For comparison, Fig. 7e shows x-ray diffraction patterns for the commercial
ZrH2,
and Fig.7f shows x-ray diffraction pattern for commercial zirconium oxide,
Zr02
(purchased from Alfa Aesar, purity 95 % powder). .
As in the case of titanium, a series of comparative materials were also
prepared, namely: ZrH2 ball milled without any additions, ball milled Zr02, a
ball
milled mixture of ZrH2 and Zr02. All these processes were performed under
identical
ball milling conditions as used for the new catalyst, with the same
parameters, and
using the same technique of loading and handling.
As found with the titanium example, only ball milled ZrH2 exhibited x-ray
diffraction pattern similar to the diffraction' pattern of our catalyst, and
all other
materials showed formation of oxide-type phases.
Catalytic properties of the Zr-based catalyst were evaluated in the process of
hydrogenation of zirconium, i.e. in the process of formation of zirconium
hydride.
Usually, formation of zirconium hydride is performed at temperatures around
400°C,
and according to "Compilation of IEA/DOEISNL Hydride Databases" by G. Sandrock
and G. Thomas http://hydpark.ca.sandia.aov, zirconium exhibits good reaction
rates
at these temperatures.
In our hydrogenation experiments, zirconium powder (purchased from Alfa
Aesar, with purity 95.+%, average powder size 2-3micron), was dried as
described
above. Subsequently, zirconium powder was mixed with 10 wt.% of the new Zr-
based catalyst (prepared from each of zirconium metal and zirconium hydride,
as
described above) and ball milled (in SPEX CentriPrep 8000M Mixer/Mill) for a
short
period of time (less than 1. hour) in order to provide good distribution, of
the catalyst
over zirconium powder. Fig.Ba shows x-ray diffraction pattern of the starting
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commercial powder, and Fig.Bb presents x-ray diffraction pattern of Zr after
introducing the catalyst by ball milling. Broader Bragg's reflections as
compared to
the starting material reflect the effects of strain, defects and
nanocrystalline structure
introduced by ball milling.
Hydrogen absorption of the material was measured in an automated,
computer controlled gas titration system. Zirconium powder catalyzed by the
new
zirconium-based catalyst was transferred from the ball milling vial into the
titration
system holder and after evacuation of the apparatus (without any preheating or
conditioning), hydrogen gas was introduced at room temperature under the
pressure
of about 1 bar. A very fast reaction of hydrogen absorption was immediately
observed, which was subsfiantially complete in under 10 seconds, as shown in
Fig.9.
In comparative experiments, zirconium powder without additions, and
zirconium powder intermixed by short ball milling (1 hr) with additions of the
before-
mentioned comparative materials, were applied to the com zirconium powder
(i.e.
dry, ball-milled ZrH2, ball-milled Zr02, and their mixture), and similar
hydrogenation
experiments to those involving the new Zr-based catalyst were carried out. In
the
comparative cases, zirconium hydride was not formed within a comparable period
of
time, as shown in Fig. 9.
In another experiment, hydrogen pressure used for absorption (without any
activation or preheating) was as low as 300 mbars, and the formation of
zirconium
hydride from the catalyzed zirconium occurred within less than 100 min., as
shown in
Fig.10. X-ray diffraction pattern shown in Fig.Bc illustrates catalyzed Zr
powder after
hydrogenation, which confirms formation of zirconium hydride under the applied
conditions (room temperature, no activation, hydrogen pressure between 300
mbars
and 1 bar).
Exam le 3: Use of Metal Oxides in Catal st Formation
The following experiments describe examples of various methods and
compositions to produce new catalysts with outstanding catalytic ability. One
important variation is the use of metal oxides as donors of the
electronegative
element. The advantage of the use of easily reducing oxides in combinafiion
with
liquids (such as water and alcohol) in the ball milling process, is that the
contribution
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of the electronegative element is in this way more easily controlled, through
a "self-
adjusting" mechanism of partial (or full) reduction of the oxide.
(a) Uses of Metal Oxides to Form Zr-Based Catalysts
Another zirconium-based catalyst was produced from zirconium hydride
(ZrH2) and copper oxide (Cu0), in a process of ball milling with a mixture of
water
and methanol. 400mg of zirconium hydride ZrH2 (Alfa Aesar, purity 99,7%, <10
micron powder) was placed in a stainless steel vial with 400mg of copper oxide
Cu0
(Alfa Aesar, purity 99.7%, -200 mesh powder) and 0.4 ml of a 1:1 molar ratio
mixture
of water and methanol (methyl alcohol HPLC grade 99,9%), together with
stainless
steel balls, giving a ball-to-powder ratio of about 20:1 on a weight basis.
The loading
was done in a glove box with protective argon atmosphere. Subsequently, the
vial
was mounted in a high-energy ball mils (SPEX CentriPrep 8000M Mixer/Mill).
Ball
milling was perFormed for 9 hours. After the process, there was no visual
presence of
the liquid phase, and the product was a black; fine powder, with very small
reddish
particles, visible under magnifying glass. X-ray diffraction pattern of this
material
(Fig.12c) indicates that at least a portion of Cu0 was reduced during the
milling
process, and Bragg's reflection characteristic for metallic copper appeared in
the
spectrum (x-ray diffraction pattern of commercial Cu is shown in Fig. 12d for
comparison). This material was subsequently used as a catalyst in the non-
temperature hydrogenation reaction of zirconium, under conditions similar to
those
for the corresponding experiments in Example 2. Fig. 11 illustrates the
hydrogenation kinetics characteristic of the Zr-based catalyst prepared, as
above,
from a mixture of ZrH2 and CuO, and then intermixed with zirconium powder to
render the system which then was hydrogenated. Fig. 11 also comparatively
illustrates the hydrogenation kinetics characteristic of the Zr-based catalyst
prepared
from ZrH2 and Cu0 versus Zr-based catalysts prepared from Zr and ZrH2 (as per
Example 2). Each catalyst appears to be substantially equally effective in
improving
the kinetics of the hydrogenation.
A further zirconium-based catalyst was produced from zirconium hydride ZrH2
and iron oxide FeO, in a process of ball milling with a mixture of water and
methanol.
400mg of zirconium hydride ZrH2 (Alfa Aesar, purity 99.7%, <10 micron powder)
was
placed in a stainless steel vial with 400mg of iron oxide Fe0 (Alfa Aesar,
purity'
99.5%, -10 mesh powder) and 0.4 ml of a 1:1 molar ratio mixture of water and
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methanol (methyl alcohol HPLC grade 99.9%), together with stainless steel
balls,
giving a ball-to-powder ratio of about 20:1 on a weight basis. The loading was
done
in a glove box with protective argon atmosphere. Subsequently, the vial was
mounted in a high-energy ball mill (SPEX CentriPrep 8000M Mixer/Mill). Ball
milling
was performed for 9 hours. After the process, there was no visual presence of
the
liquid phase, and the product was a black, fine powder. X-ray diffraction
pattern of
this material (Fig. 14c) indicates that at least a portion of Fe0 was reduced
during
the milling process, and Bragg's reflection characteristic for metallic iron
appeared in
the spectrum (x-ray diffraction pattern of commercial Fe is shown in Fig. 14d
for
comparison).
(b) Use of Metal Oxides to Form Ti-Based Catalysts
Titanium-based catalyst was produced from titanium hydride TiH2 and copper
oxide CuO, in a process of ball milling with a mixture of water and methanol,
450 mg
of titanium hydride TiH2 (Aldrich, purity 98%, powder -325 mesh) was placed in
a~
stainless steel vial with 350mg of copper oxide Cu0 (Alfa Aesar, purity 99.7%,
-200
mesh powder) and 0.5 ml of a 1:1 molar ratio mixture of water and methanol
(methyl
alcohol HPLC grade 99.9%), together with stainless steel balls, giving a ball-
to-
powder ratio of about 20:1 on a weight basis. The loading was done in a glove
box
with protective argon atmosphere, Subsequently, the vial was mounted in a high-
energy ball mill (SPEX CentriPrep 8000M Mixer/Mill). Ball milling was
performed for
9 hours. After the process, there was no visual presence of the liquid phase,
and the
product was a black, fine powder, with uniformly distributed, very small
reddish
particles. X-ray diffraction pattern of this material (Fig.13 c) indicates
that Cu0 was
fully reduced during the milling process, and Bragg's reflection
characteristic for
metallic copper appeared in the spectrum (x-ray diffraction pattern of
commercial Cu
is shown in Fig. 13d for comparison).
Catalytic ability of this new Ti-based catalyst was evaluated in the
hydrogenation of magnesium' (i.e. in formation of magnesium hydride MgH2).
Normally, magnesium hydride is very difficult to fabricate. According to
"Compilation
of IEA/DOE/SNL Hydride Databases" by G. Sandrock and G. Thomas
http://hydpark.ca.sandia_gov, magnesium "will slowly react with H2', however
kinetics
"is generally very slow with difficulty in reaching 2.0 H/M (hydrogen:metal
ratio). In
order to activate the reaction with hydrogen, activation has to be applied,
which
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consists of heating to 325°C under vacuum. As stated in the Database,
hydrogenation of magnesium "is sensitive to 02 and H20".
Magnesium was purchased from Alfa Aesar, with 99.8% purity. As with the
experiments described above, magnesium powder (with x-ray diffraction pattern
shown in Fig.18, consistent with International Centre for Diffraction Data
database
PDF-2, card number 89-5003) was mixed with 10 wt.% of the new catalyst
(prepared
from TiH2 and CuO, and ball milled for a short period of time (less than 1
hour)) in
' order to provide good distribution of the catalyst over magnesium powder.
Hydrogen absorption capabilities of the material were measured in the
automated, computer controlled gas titration system, which allows precise
evaluation
of hydrogen uptake and release by measuring pressure changes in a closed
system.
In contrast to conventional magnesium which requires high-temperature
activation,
magnesium powder catalyzed by this new Ti-based catalyst exhibited fast
formation
of magnesium hydride at room temperature, without any activation or
preheating.
Fig. 19 shows formation of magnesium hydride from the catalyzed magnesium at
40°C, without any activation or preheating. As illustrated in Fig. 18,
after
hydrogenation, the material exhibits x-ray diffraction pattern characteristic
for MgH2,
consistent with the International Centre for Diffraction Data database PDF-2,
card
number 72-1687. As can be seen in this diffraction pattern, the presence of
small
amount of the catalyst is still visible after hydrogenation, which had not
been
consumed or significantly transformed in the hydrogenation process and remains
effective in the subsequent hydrogenation/dehydrogenation cycles.
Similar experiments have been performed to produce titanium-based catalysts
with the following oxides: magnesium oxide Mg0 (Aldrich, purity 98%),
manganese
oxide Mn0 (Alfa Aesar, purity 99%, +200 mesh powder), nickel oxide Ni0 (Alfa
Aesar, purity 99%, -325 mesh powder). X-ray diffraction patterns of some of
these
catalysts are shown in Fig. 15. .
Example 4: Cu0-Based Catalyst
Catalyst formation was observed in a series of experiments of ball-milling of
copper oxide Cu0 with water, alcohol or their mixtures. Depending on the
milling
conditions, specifically the amount of water/alcohol added, and milling time,
different
stages of reduction of Cu0 were observed, namely various mixtures of CuO +
Cu20,
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or Cu20 + Cu, or Cu0 + Cu20 +Cu. These materials exhibited exemplary catalytic
abilities, although no obvious indication of any particular M-H coordination
was seen
in the diffraction patterns. .
To prepare copper-based catalysts, 800 mg of copper oxide Cu0 (Alfa Aesar,
with purity 99.7%, - 200 mesh powder) was placed in a stainless steel vial
together
with and 0.4 ml water and stainless steel balls, giving a ball-to-powder ratio
of about
20:1 on a weight basis. The loading was done in a glove box with protective
argon
atmosphere. Subsequently, the vial was mounted in a high-energy ball mill
(SPEC
CentriPrep 8000M Mixer/Mill). Ball milling was performed for 9, 16 and 24
hours.
After the process, instead of the initial black powder, the materials
exhibited different
tones of dark-green and brownish colors, with no visual presence of the liquid
phase.
X-ray diffraction pattern of these powders show various mixtures of CuO, Cu20
and
Cu, depending on the milling time (Fig. 16).
Example 5: Catalyzed Dehydroaenation of LiAIH4
Decomposition (i.e. dehydrogenation) of LiAIH4 was catalyzed by' an
embodiment of a catalyst composition of the present invention. This hydride is
known
to be very sensitive to any traces of H20 and has to be stored with great
care, under
protective atmosphere of dry gas (MSDS datasheet from the material supplier).
Normally, LiAIH4 is relatively stable, even at elevated temperatures and
decomposes
slowly with hydrogen release up to 5.6 wt.% when heated up to at least 140-
160°C.
LiAIH4 (lithium tetrahydridoaluminate) was purchased from Alfa Aesar, with
purity 95+%. Two samples were prepared under similar conditions; one from
LiAIH4
without any addition, and the other - with a catalyst prepared from ZrH2 + Cu0
+ Zn
+ water/methanol mixture, in analogous way as the catalysts described in
previous
examples). Subsequently, LiAIH4 powder was mixed with 10 wt.% of the new
catalyst
and ball milled (in SPEX CentriPrep 8000M Mixer/Mill) for a short period of
time (less
than 1 hour) in order to provide good distribution of the catalyst over
zirconium
powder. The comparative sample of LiAIH4 was also ball milled in the same way.
Hydrogen desorption of the material was measured in an automated,
computer controlled gas titration system. The material was transferred from
the ball
milling vial into the titration system holder and after evacuation of the
apparatus,
hydrogen gas release was measured. During the experiment, the system was
heated
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up to 95°C, and then kept at constant temperature, while measuring
hydrogen
release from the sample. As seen in Fig. 20, the non-catalyzed (but ball
milled)
sample of LiAIH4 did not show any significant hydrogen release in this
temperature/time scale, but the catalyzed LAIH4 exhibited fast
dehydrogenation,
which started at temperatures about 70-80°C and was completed with good
kinetics
without exceeding 100°C. It is important to note that in this case
hydrogen desorption
occurs below the melting temperature of LiAIH4 (125°C), which
emphasizes the
efficiency of the catalyst.
Example 6: Catalyzed HydroaenationlDehydroaenation of NaAIHa
Hydrogenation/dehydrogenation of NaAIH4, (which is a sodium analog of
LiAIH4) was catalyzed by an embodiment of a catalyst composition of the
present
invention. NaAIH4 has also similar sensitivity to moisture and H20 traces as
LiAIH4,
and normally can be decomposed (dehydrogenated) only at temperatures close to
its
melting temperature, i.e. 180°C.
NaAIH4 (sodium aluminum hydride) was purchased from Aldrich (purity 90%,
dry). As in the previous example, two samples were prepared under similar
conditions: one from NaAIH4 without any addition, and the other - with a
catalyst
prepared from TiH2 + Cu0 + water/methanol mixture, in similar way as the
catalysts
described in previous examples). NaAIH4 sample was mixed with 10 wt.% of the
new
catalyst and ball milled (in SPEX CentriPrep 8000M Mixer/Mill) for a short
period of
time (less than 1 hour) in order to provide good distribution of the catalyst.
The
comparative sample of NaAIH4 was also ball milled in the same way.
Hydrogen desorption of these samples was measured in an automated,
computer controlled gas titration system. The material was transferred from
the ball
milling vial into the titration system holder and after evacuation of the
apparatus,
hydrogen gas release was measured. During the experiment, the system was
heated
up to 300°C with a constant heating rate of 1 deg/mmin., while
monitoring the
hydrogen release. As seen in Fig. 21, the non-catalyzed (but ball milled)
sample of
NaAIH4 showed hydrogen release only at temperatures close to the melting
temperature, i.e. around 180°C. By contrast, the catalyzed sample
started desorbing
hydrogen even at temperatures below 100'C.
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In the subsequent hydrogenation/dehydrogenation cycles, the catalyst did not
lose its catalytic ability and remained visible in the diffraction pattern in
a similar way
as shown in the example of hydrogenated magnesium (Fig. 18).
Hydrogenation/dehydrogenation cycling was performed for similarly prepared
samples of NaAIH4 with a series of catalysts of the present invention, in
experiments
analogous to those described above. Figs. 22 and 23 show dehydrogenation
kinetics
of NaAIH4 catalyzed with a catalyst prepared from TiH2 + Ni0 + methanol (shown
in
Fig. 15b). Dehydrogenation was performed at various temperatures: 140, 120 and
100°C, showing unsurpassed kinetics. Fig. 24 shows hydrogen desorption
from
NaAIH4 catalyzed by a catalyst prepared from TiH2 + Mg0 +methanol (X-ray
diffraction shown in Fig.15c).
Example 7: Use of Reducing Accent in Catalyst Formation
Another approach in the production of the new catalysts is to introduce
reducing elements or compounds into the process of the catalyst preparation.
These
reducing additions, which are easily oxidized when necessary, can protect the
metallic substance against oxidation. Examples of suitable additions include
aluminium, magnesium, zinc, rare earth metals or carbon. In another approach,
an
addition is used that could act either as a reducing addition or as part of
the required
M-H configuration, depending on the process specifics. Such additions could be
for
example vanadium or manganese, which can act as protectors against oxidation
for
example in water-containing process, but can also form their own hydride-type
configurations in ball milling with, for example, methanol.
A zirconium-based catalyst was produced from zirconium hydride (ZrH2) and
vanadium, in a process of ball milling with methanol, 350 mg of zirconium
hydride
(Alfa Aesar, purity 99.7%, powder < 10 micron powder) was placed in a
stainless
steel vial with 450mg of vanadium (Alfa Aesar, purity 99.5%, -20 mesh
granules) and
0.5 ml methanol (methyl alcohol HPLC grade 99.9%), together with stainless
steel
balls, giving a ball-to-powder ratio of about 20:1 on a weight basis. The
loading was
done in a glove box with protective argon atmosphere. Subsequently, the vial
was
mounted in a high-energy ball mill (SPEX CentriPrep 8000M Mixer/Mill). Ball
milling
was performed for 9 hours. After the process, the resulting product was a
black, fine
powder. X-ray diffraction pattern of this material (Fig. 16c) indicates that
vanadium
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transformed into hydride-type coordination (at least partially) during the
milling
process, and Bragg's reflection characteristic for vanadium hydride (according
to
International Centre for Diffraction Data database PDF-2, card number 891890
appeared in the spectrum).
It will be understood, of course, that modifications can be made to the
embodiments of the invention described herein without departing from the scope
and
the purview of the invention as defined by the appended claims.
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