Note: Descriptions are shown in the official language in which they were submitted.
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Layered Support Material for Catalysts
Field of the Invention
[0002] The present invention relates to catalysts, methods of making the
catalysts, and
methods of making alkenyl alkanoates. More particularly, the invention relates
to methods of
making vinyl acetate.
Background of the Invention
(0003] Certain alkenyl alkanoates, such as vinyl acetate (VA), are commodity
chemicals in
high demand in their monomer form. For example, VA is used to make polyvinyl
acetate
(PVAc), which is used commonly for adhesives, and accounts for a large portion
of VA use.
Other uses for VA included polyvinyl alcohol (PVOH), ethylene vinyl acetate
(EVA), vinyl
acetate ethylene (VAE), polyvinyl butyral (PVB), ethylene vinyl alcohol
(EVOH), polyvinyl
formal (PVF), and vinyl chloride-vinyl acetate copolymer. PVOH is typically
used for textiles,
films, adhesives, and photosensitive coatings. Films and wire and cable
insulation often employ
EVA in some proportion. Major applications for vinyl chloride-vinyl acetate
copolymer include
coatings, paints, and adhesives often employ VAE having VA in some proportion.
VAE, which
contains more than 50 percent VA, is primarily used as cement additives,
paints, and adhesives.
PVB is mainly used for under layer in laminated screens, coatings, and inks.
EVOH is used for
barrier films and engineering polymers. PVF is used for wire enamel and
magnetic tape.
[0004] Because VA is the basis for so many commercially significant materials
and products,
the demand for VA is large, and VA production is frequently done on a
relatively large scale, e.g.
50,000 metric tons or more per year. This large scale production means that
significant
economies of scale are possible and relatively subtle changes in the process,
process conditions
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or catalyst characteristics can have a significant economic impact on the cost
of the production of
VA.
[0005] Many techniques have been reported for the production of alkenyl
alkanoates. For
example, in making VA, a widely used technique includes a catalyzed gas phase
reaction of
ethylene with acetic acid and oxygen, as seen in the following reaction:
C2H4 + CH3000H + 0.5 02 D CH3000CH=CH2 + H2O
Several
side reactions may take place, including, such as, the formation of CO2. The
results of this
reaction are discussed in terms of the space-time yield (STY) of the reaction
system, where the
STY is the grams of VA produced per liter of catalyst per hour of reaction
time (g/l*,h).
[0006] The composition of the starting material feed can be varied within wide
limits.
Typically, the starting material feed includes 30-70% ethylene, 10-30% acetic
acid and 4-16%
oxygen. The feed may also include inert materials such as C02, nitrogen,
methane, ethane,
propane, argon and/or helium. The primary restriction on feed composition is
the oxygen level in
the effluent stream exiting the reactor must be sufficiently low such that the
stream is outside the
flammability zone. The oxygen level in the effluent is affected by the oxygen
level inc the starting
material stream, 02 conversion rate of the reaction and the amount of any
inert material in the
effluent.
[0007] The gas phase reaction has been carried out where a feed of the
starting materials is
passed over or through fixed bed reactors. Successful results have been
obtained through the use
of reaction temperatures in the range of - 125 C to 200 C, while reaction
pressures of, 1-15
atmospheres are typical.
[0008] While these systems have provided adequate yields, there continues to
be a need for
reduced production of by-products, higher rates of VA output, and lower energy
use during
production. One approach is to improve catalyst characteristics, particularly
as to CO2 selectivity
and/or activity of the catalyst. Another approach is to modify reaction
conditions, such as the
ratio of starting materials to each other, the 02 conversion of the reaction,
the space velocity (SV)
of the starting material feed, and operating temperatures and pressures.
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[0009] The formation of CO2 is one aspect which may be reduced through the use
of
improved catalysts. The CO2 selectivity is the percentage of the ethylene
converted that goes to
CO2. Decreasing the CO2 selectivity permits a larger amount of VA per unit
volume and unit
time in existing plants, even retaining all other reaction conditions.
[0010] VA output of a particular reaction system is affected by several other
factors
including the activity of the catalyst, the ratio of starting materials to
each other, the 02
conversion of the reaction, the space velocity (SV) of the starting material
feed, and operating
temperatures and pressures. All these factors cooperate to determine the space-
time yield (STY)
of the reaction system, where the STY is discussed in terms of grams of VA
produced per liter of
catalyst per hour of reaction time or g/l*h.
[0011] Generally, activity is a significant factor in determining the STY, but
other factors
may still have a significant impact on the STY. Typically, the higher the
activity of a catalyst,
the higher the STY the catalyst is able to produce.
[0012] The 02 conversion is a measure of how much oxygen reacts in the
presence of the
catalyst. The 02 conversion rate is temperature dependent such that the
conversion rate generally
climbs with the reaction temperature. However, the amount of CO2 produced also
increases
along with the 02 conversion. Thus, the 02 conversion rate is selected to give
the desired VA
output balanced against the amount of CO2 produced. A catalyst with a higher
activity means
that the overall reaction temperature can be lowered while maintaining the
same 02 conversion.
Alternatively, a catalyst with a higher activity will give a higher 02
conversion rate at a given
temperature and space velocity.
[0013] It is common that catalysts employ one or more catalytic components
carried on a
relatively inert support material. In the case of VA catalysts, the catalytic
components are
typically a mixture of metals that may be distributed uniformly throughout the
support material
("all through-out catalysts"), just on the surface of the support material
("shell catalysts"), just
below a shell of support material ("egg white catalysts") or in the core of
the support material
("egg yolk catalysts").
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[0014] Numerous different types of support materials have been suggested for
use in VA
catalyst including silica, cerium doped silica, alumina, titania, zirconia and
oxide mixtures. But
very little investigation of the differences between the support materials has
been done. For the
most part, only silica and alumina have actually been commercialized as
support materials.
[0015] One useful combination of metals for VA catalysis is palladium and
gold. Pd/Au
catalysts provide adequate CO2 selectivity and activity, but there continues
to be a need for
improved catalysts given the economies of scale that are possible in the
production of VA.
[0016] One process for making Pd/Au catalysts typically includes the steps of
impregnating
the support with aqueous solutions of water-soluble salts of palladium and
gold; reacting the
impregnated water-soluble salts with an appropriate alkaline compound e.g.,
sodium hydroxide,
to precipitate (often called fixing) the metallic elements as water-insoluble
compounds, e.g. the
hydroxides; washing the fixed support material to remove un-fixed compounds
and to otherwise
cleanse the catalyst of any potential poisons, e.g. chloride; reducing the
water insoluble
compounds with a typical reductant such as hydrogen, ethylene or hydrazine,
and adding an
alkali metal compound such as potassium or sodium acetate.
[0017] Various modifications to this basic process have been suggested. For
example, in
U.S. Patent No. 5,990,344, it is suggested that sintering of the palladium be
undertaken after the
reduction to its free metal form. In U.S. Patent No. 6,022,823, it suggested
that calcining the
support in a non-reducing atmosphere after impregnation with both palladium
and gold salts
might be advantageous. In WO94/21374, it is suggested that after reduction and
activation, but
before its first use, the catalyst may be pretreated by successive heating in
oxidizing, inert, and
reducing atmospheres.
[0018] In U.S. Patent No. 5,466,652, it is suggested that salts of palladium
and gold that are
hydroxyl-, halide- and barium-free and soluble in acetic acid may be useful to
impregnate the
support material. A similar suggestion is made in U.S. Patent No. 4,902,823,
i.e. use of halide-
and sulfur-free salts and complexes of palladium soluble in unsubstituted
carboxylic acids having
two to ten carbons.
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[0019] In U.S. Patent No. 6,486,370, it suggested that a layered catalyst may
be used in a
dehydrogenation process where the inner layer support material differs from
the outer layer
support material. Similarly, U.S. Patent No. 5,935,889 suggests that a layered
catalyst may
useful as acid catalysts. But neither suggests the use of layered catalysts in
the production of
alkenyl alkanoates.
10020] Taken together, the inventors have recognized and addressed the need
for continued
improvements in the field of VA catalysts to provide improved VA production at
lower costs.
Summary of the Invention
[0021] The present invention addresses at least four different aspects
relating to catalyst
structure, methods of making those catalysts and methods of using those
catalysts for making
alkenyl alkanoates. Separately or together in combination, the various aspects
of the invention
are directed at improving the production of alkenyl alkanoates and VA in
particular, including
reduction of by-products and improved production efficiency. A first aspect of
the present
invention pertains to a unique palladium/gold catalyst or pre-catalyst
(optionally calcined) that
includes rhodium or another metal. A second aspect pertains to a
palladium/gold catalyst or pre-
catalyst that is based on a layered support material where one layer of the
support material is
substantially free of catalytic components. A third aspect pertains to a
palladium/gold catalyst or
pre-catalyst on a zirconia containing support material. A fourth aspect
pertains to a
palladium/gold catalyst or pre-catalyst that is produced from substantially
chloride free catalytic
components.
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[0021 a] In one aspect, the invention relates to a method of producing a
catalyst or pre-catalyst for the production of alkenyl alkanoates, comprising:
layering a first support material and a surfactant or bonding agent onto a
second
support material to produce a particulate, layered support material having an
outer
layer and an inner layer, wherein catalytic components of palladium, gold or
combinations thereof are contained in the outer layer of the layered support
material.
[0021b] In a further aspect, the invention relates to a composition for
catalyzing the production of alkenyl alkanoates, comprising: a particulate,
layered
support material comprising at least an outer layer comprising a first support
material layer, a surfactant or bonding agent and an inner layer comprising a
second support material wherein the outer layer comprises at least palladium
in
combination with gold contacted thereon to form a catalyst or pre-catalyst,
wherein
the inner layer is free of palladium and gold.
[0021c] In a still further aspect, the invention relates to a method of
producing alkenyl alkanoates, comprising: contacting a feed comprising an
alkene, an alkanoic acid and an oxidizer to a catalyst or pre-catalyst
comprising
palladium in combination with gold on a particulate, layered support material
comprising at least an inner support material, a surfactant or bonding agent
and
an outer support material.
Detailed Description
[0022] Catalysts
[0023] For present purposes, a catalyst is any support material that
contains at least one catalytic component and that is capable of catalyzing a
reaction, whereas a pre-catalyst is any material that results from any of the
catalyst preparation steps discussed herein.
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[0024] Catalysts and pre-catalysts of the present invention may include those
having at least
one of the following attributes: 1) the catalyst will be a palladium and gold
containing catalyst
that includes at least another catalytic component, e.g. rhodium where the one
or more of the
catalytic components have been calcined; 2) the catalyst will be carried on a
layered support, 3)
the catalyst will be carried on a zirconia containing support material; 4) the
catalyst will be
produced with chloride free precursors or any combination of the foregoing.
Effective use of the
catalyst accordingly should help improve CO2 selectivity, activity or both,
particularly as
pertaining to VA production.
[0025] It should be appreciated that the present invention is described in the
context of
certain illustrative embodiments, but may be varied in any of a number of
aspects depending on
the needs of a particular application. By way of example, without limitation,
the catalysts may
have the catalytic components uniformly distributed throughout the support
material or they may
be shell catalysts where the catalytic components are found in a relatively
thin shell around a
support material core. Egg white catalysts may also be suitable, where the
catalytic components
reside substantially away from the center of support material. Egg yolk
catalysts may also be
suitable.
[0026] Catalytic Components
[0027] In general, the catalysts and pre-catalysts of the present invention
include metals and
particularly include a combination of at least two metals. In particular, the
combination of metals
includes at least one from Group VIIIB and at least one from Group IB. It will
be appreciated
that "catalytic component" is used to signify the metal that ultimately
provides catalytic
functionally to the catalyst, but also includes the metal in a variety of
states, such as salt,
solution, sol-gel, suspensions, colloidal suspensions, free metal, alloy, or
combinations thereof.
Preferred catalysts include palladium and gold as the catalytic components.
[00281 One embodiment of the catalyst includes a combination of catalytic
components
having palladium and gold combined with a third catalytic component. The third
catalytic
component is preferably selected from Group VIIIB, with Rh being the most
preferred. Other
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preferred catalysts include those where the third catalytic component is
selected from W, Ni, Nb,
Ta, Ti, Zr, Y, Re, Os, Fe, Cu, Co, Zn, In, Sn, Ce, Ge, Ga and combinations
thereof.
[0029] Another embodiment of the catalyst includes a combination of catalytic
components
including proportions of palladium, gold, and rhodium. Optionally a third
catalytic component
(as listed above) may also be included in this embodiment in place of Rh. In
another
embodiment, two or more catalytic components from the above list may be
employed.
[0030] In one example, palladium and gold may be combined with Rh to form a
catalyst that
shows improved CO2 selectively (i.e. decreased formation of C02) compared to
Pd/Au catalysts
that lack Rh. Also, the addition of Rh does not appear to adversely affect the
activity of the
catalyst. The CO2 selectivity of the palladium, gold, rhodium catalyst may
also be improved
through calcining during the catalyst preparation and/or through the use of
water-soluble halide
free precursors (both discussed below), although these are not necessary to
observe the Rh effect.
[0031] The atomic ratio of the third catalytic component to palladium may be
in the range of
about 0.005 to about 1.0, more preferably about 0.01 to about 1Ø In one
embodiment, the
catalyst contains between about 0.01 and about 5.0 g of the third catalytic
component per liter of
catalyst.
[0032] Another preferred embodiment of the catalyst includes between about 1
to about 10
grams of palladium, and about 0.5 to about 10 grams of gold per liter of
catalyst. The amount of
gold is preferably from about 10 to about 125 wt % based on the weight of
palladium.
[0033] In one embodiment for ground catalysts, Au to Pd atomic ratios between
about 0.5
and about 1.00 may be preferred for ground catalysts. The atomic ratio can be
adjusted to
balance the activity and CO2 selectivity. Employment of higher Au/Pd weight or
atomic ratios
tends to favor more active, more selective catalysts. Stated alternatively, a
catalyst with an
atomic ratio of about 0.6 is less selective for CO2, but also has less
activity than a catalyst with a
ratio of about 0.8. The effect of the high Au/Pd atomic ratio on ground
support material may
also be enhanced through the use of relatively high excess of hydroxide ion,
as discussed below
with respect to the fixing step. A ground catalyst may be one where the
catalytic components are
contacted to the support material followed by a reduction in the particle size
(e.g. by grinding or
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ball milling) or one where the catalytic components are contacted to the
support material after the
support material has been reduced in size.
[0034] For shell catalysts, the thickness of the shell of catalytic components
on the support
material ranges from about 5 m to about 500 m. More preferred ranges include
from about 5
m to about 300 m.
[0035] Support Materials
[0036] As indicated, in one aspect of the invention, the catalytic components
of the present
invention generally will be carried by a support material. Suitable support
materials typically
include materials that are substantially uniform in identity or a mixture of
materials. Overall, the
support materials are typically inert in the reaction being performed. Support
materials may be
composed of any suitable substance preferably selected so that the support
materials have a
relatively high surface area per unit mass or volume, such as a porous
structure, a molecular sieve
structure, a honeycomb structure, or other suitable structure. For example,
the support material
may contain silica, alumina, silica-alumina, titania, zirconia, niobia,
silicates, aluminosilicates,
titanates, spinel, silicon carbide, silicon nitride, carbon, cordierite,
steatite, bentonite, clays,
metals, glasses, quartz, pumice, zeolites, non-zeolitic molecular sieves
combinations thereof and
the like. Any of the different crystalline form of the materials may also be
suitable, e.g. alpha or
gamma alumina. Silica and zirconia containing support materials are the most
preferred. In
addition, multilayer support materials are also suitable for use in the
present invention.
[0037] The support material in the catalyst of this invention may be composed
of particles
having any of various regular or irregular shapes, such as spheres, tablets,
cylinders, discs, rings,
stars, or other shapes. The support material may have dimensions such as
diameter, length or
width of about 1 to about 10 mm, preferably about 3 to about 9 mm. In
particular having a
regular shape (e.g. spherical) will have as its preferred largest dimension of
about 4 mm to about
8 mm. In addition, a ground or powder support material may be suitable such
that the support
material has a regular or irregular shape with a diameter of between about 10
microns and about
1000 micron, with preferred sizes being between about 10 and about 700
microns, with most
preferred sizes being between about 180 microns and about 450 microns. Larger
or smaller sizes
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may be employed, as well as polydisperse collections of particles sizes. For
example, for a fluid
bed catalyst a preferred size range would include 10 to 150 microns. For
precursors used in
layered catalysts, a size range of 10 to 250 microns is preferred.
[0038] Surface areas available for supporting catalytic components, as
measured by the BET
(Brunauer, Emmett, and Teller) method, may generally be between about 1 m2/g
and about 500
m2/g, preferably about 100 m2/g to about 200 m2/g. For example, for a porous
support, the pore
volume of the support material may generally be about 0.1 to about 2 ml/g, and
preferably about
0.4 to about 1.2 ml/g. An average pore size in the range, for example, of
about 50 to about 2000
angstroms is desirable, but not required.
[0039] Examples of suitable silica containing support materials include KA160
from Sud
Chemie, Aerolyst350 from Degussa and other pyrogenic or microporous-free
silicas with a
particle size of about 1 mm to about 10 mm.
[0040] Examples of suitable zirconia containing support materials include
those from
NorPro, Zirconia Sales (America), Inc., Daichi Kigenso Kagaku Kogyo, and
Magnesium
Elektron Inc (MEI). Suitable zirconia support materials have a wide range of
surface areas from
less than about 5 m2/g to more than 300 m2/g. Preferred zirconia support
materials have surface
areas from about 10 m2/g to about 135 m2/g. Support materials may have their
surfaces treated
through a calcining step in which the virgin support material is heated. The
heating reduces the
surface area of the support material (e.g. calcining). This provides a method
of creating support
materials with specific surface areas that may not otherwise be readily
available from suppliers.
[0041] In another embodiment, it is contemplated to employ at least a plural
combination of
support materials, each with a different characteristic. For example, at least
two support
materials (e.g. zirconia) with different characteristics may exhibit different
activities and CO2
selectivities, thus permitting preparation of catalysts with a desired set of
characteristics, i.e.
activity of a catalyst may be balanced against the CO2 selectivity of the
catalyst.
[0042] In one embodiment, plural different supports are employed in a layered
configuration.
Layering may be achieved in any of a number of different approaches, such as a
plurality of
lamella that are generally flat, undulated or a combination thereof. One
particular approach is to
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utilize successively enveloping layers relative to an initial core layer. In
general, herein, layered
support materials typically include at least an inner layer and an outer layer
at least partially
surrounding the inner layer. The outer layer preferably contains substantially
more of catalytic
components than the inner layer. In one embodiment, the inner and outer layers
are made of
different materials; but the materials may be the same. While the inner layer
may be non-porous,
other embodiments include an inner layer that is porous.
[00431 The layered support material preferably results in a form of a shell
catalyst. But the
layered support material offers a well defined boundary between the areas of
the support material
that have catalytic components and the areas that do not. Also, the outer
layer can be constructed
consistently with a desired thickness. Together the boundary and the uniform
thickness of the
outer layer result in a shell catalyst that is a shell of catalytic components
that is of a uniform and
known thickness.
[00441 Several techniques are known for creating layered support materials
includes those
described in U.S. Patent Nos. 6,486,370; 5,935,889; and 5,200,382,.
In one embodiment, the materials of the inner layer are also not
substantially penetrated by liquids, e.g., metals including but not limited to
aluminum, titanium
and zirconium. Examples of other materials for the inner layer include, but
are not limited to,
alumina, silica, silica-alumina, titania, zirconia, niobia, silicates,
aluminosilicates, titanates,
spinel, silicon carbide, silicon nitride, carbon, cordierite, steatite,
bentonite, clays, metals,
glasses, quartz, pumice, zeolites, non-zeolitic molecular sieves and
combinations thereof. A
preferred inner layer is silica and KA160, in particular.
[0045] These materials which make up the inner layer may be in a variety of
forms such as
regularly shaped particulates, irregularly shaped particulates, pellets,
discs, rings, stars, wagon
wheels, honeycombs or other shaped bodies. A spherical particulate inner layer
is preferred. The
inner layer, whether spherical or not, has an effective diameter of about 0.02
mm to about 10.0
mm and preferably from about 0.04 mm to about 8.0 mm.
[00461 The outermost layer of any multilayer structure is one which is porous,
has a surface
area in the range of about 5 m2/g to about 300 m2/g. The material of the outer
layer is a metal,
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ceramic, or a combination thereof, and in one embodiment it is selected from
alumina, silica,
silica-alumina, titania, zirconia, niobia, silicates, aluminosilicates,
titanates, spinet, silicon
carbide, silicon nitride, carbon, cordierite, steatite, bentonite, clays,
metals, glasses, quartz,
pumice, zeolites, non-zeolitic molecular sieves and combinations thereof and
preferably include
alumina, silica, silica/alumina, zeolites, non-zeolite molecular sieves
(NZMS), titania, zirconia
and mixtures thereof. Specific examples include zirconia, silica and alumina
or combinations
thereof.
[0047] While the outer layer typically surrounds substantially the entire
inner layer, this is not
necessarily the case and a selective coating on the inner layer by the outer
layer may be
employed.
[0048] The outer layer may be coated on to the underlying layer in a suitable
manner. In one
embodiment, a slurry of the outer layer material is employed. Coating of the
inner layer with the
slurry may be accomplished by methods such as rolling, dipping, spraying, wash
coating, other
slurry coating techniques, combinations thereof or the like. One preferred
technique involves
using a fixed or fluidized bed of inner layer particles and spraying the
slurry into the bed to coat
the particles evenly. The slurry may be applied repeatedly in small amounts,
with intervening
drying, to provide an outer layer that is highly uniform in thickness.
[0049] The slurry utilized to- coat the inner layer may also include any of a
number of
additives such as a surfactant, an organic or inorganic bonding agent that
aids in the adhesion of
the outer layer to an underlying layer, or combinations thereof. Examples of
this organic bonding
agent include but are not limited to PVA, hydroxypropylcellulose, methyl
cellulose, and
carboxymethylcellulose. The amount of organic bonding agent which is added to
the slurry may
vary, such as from about 1 wt % to about 15 wt % of the combination of outer
layer and the
bonding agent. Examples of inorganic bonding agents are selected from an
alumina bonding
agent (e.g. Bohmite), a silica bonding agent (e.g. Ludox, Teos), zirconia
bonding agent (e.g.
zirconia acetate or colloidal zirconia) or combinations thereof. Examples of
silica bonding
agents include silica sot and silica gel, while examples of alumina bonding
agents include
alumina sot, bentonite, Bohmite, and aluminum nitrate. The amount of inorganic
bonding agent
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may range from about 2 wt % to about 15 wt % of the combination of the outer
layer and the
bonding agent. The thickness of the outer layer may range from about 5 microns
to about 500
microns and preferably between about 20 microns and about 250 microns.
[0050] Once the inner layer is coated with the outer layer, the resultant
layered support will
be dried, such as by heating at a temperature of about 100 C to about 320 C
(e.g. for a time of
about 1 to about 24 hours) and then may optionally be calcined at a
temperature of about 300 C
to about 900 C (e.g. for a time of about 0.5 to about 10 hours) to enhance
bonding the outer layer
to it underlying layer over a least a portion of its surface and provide a
layered catalyst support.
The drying and calcining steps can be combined into one step. The resultant
layered support
material may be contacted with catalytic components just as any other support
material in the
production of catalysts, as described below. Alternately, the outer layer
support material is
contacted to catalytic components before it is coated onto the underlying
layer.
[0051] In another embodiment of the layered support, a second outer layer is
added to
surround the initial outer layer to form at least three layers. The material
for the second outer
layer may be the same or different than the first outer layer. Suitable
materials include those
discussed with respect to the first outer layer. The method for applying the
second outer layer
may be the same or different than the method used to apply the middle layer
and suitable
methods include those discussed with respect to the first outer layer. Organic
or inorganic
bonding agents as described may suitably used in the formation of the second
outer layer.
[0052] The initial outer layer may or may not contain catalytic components.
Similarly, the
second outer layer may or may not contain catalytic components. If both outer
layers contain
catalytic component, then preferably different catalytic components are used
in each layer,
although this is not necessarily the case. In one preferred embodiment, the
initial outer layer
does not contain a catalytic component. Contacting catalytic component to the
outer layers may
be accomplished by impregnation or spray coating, as described below.
[0053] In embodiments where the initial outer layer contains catalytic
component, one
method of achieving this is to contact the catalytic component to the material
of the initial outer
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layer before the material is applied to the inner layer. The second outer
layer may be applied to
the initial outer layer neat or containing catalytic component.
[0054] Other suitable techniques may be used to achieve a three layered
support material in
which one or more of the outer layers contain catalytic components. Indeed,
the layered support
material is not limited to three layers, but may include four, five or more
layers, some or all of
which may contain catalytic components.
[0055] In addition, the number and type of catalytic components that vary
between the layers
of the layered support material, other characteristics (e.g. porosity,
particle size, surface area,
pore volume, or the like) of the support material may vary between the layers.
[0056] Methods Of Making Catalysts
[0057] In general the method includes contacting support material catalytic
components and
reducing the catalytic components. Preferred methods of the present invention
include
impregnating the catalytic components into the support material, calcining the
catalytic
component containing support material, reducing the catalytic components and
modifying the
reduced catalytic components on the support material. Additional steps such as
fixing the
catalytic components on the support material and washing the fixed catalytic
components may
also be included in the method of making the catalyst or pre-catalyst. Some of
the steps listed
above are optional and others may be eliminated (e.g. the washing and/fixing
steps). In addition,
some steps may be repeated (e.g. multiple impregnation or fix steps) and the
order of the steps
may be different from that listed above (e.g. the reducing step precedes the
calcining step). To a
certain extent, the contacting step will determine what later steps are needed
for the formation of
the catalyst.
[0058] Contacting Step
[0059] One particular approach to contacting is one pursuant to which an egg
yolk catalyst or
pre-catalyst is formed, an egg white catalyst or pre-catalyst is formed, an
all throughout catalyst
or pre-catalyst is formed or a shell catalyst or pre-catalyst is formed, or a
combination thereof. In
one embodiment, techniques that form shell catalysts are preferred.
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[0060] The contacting step may be carried out using any of the support
materials described
above, with silica, zirconia and layered support materials containing zirconia
being the most
favored. The contacting step is preferably carried out at ambient temperature
and pressure
conditions; however, reduced or elevated temperatures or pressures may be
employed.
[00611 In one preferred contacting step, a support material is impregnated
with one or more
aqueous solutions of the catalytic components (referred to as precursor
solutions). The physical
state of the support material during the contacting step may be a dry solid, a
slurry, a sol-gel, a
colloidal suspension or the like.
[0062] In one embodiment, the catalytic components contained in the precursor
solution are
water soluble salts made of the catalytic components, including but not
limited to, chlorides,
other halides, nitrates, nitrites, hydroxides, oxides, oxalates, acetates
(OAc), and amines, with
halide free salts being preferred and chloride free salts being more
preferred. Examples of
palladium salts suitable for use in precursor solutions include PdC12,
Na2PdC14, Pd(NH3)2(NO2)2,
Pd(NH3)4(OH)2, Pd(NH3)4(NO3)2, Pd(N03)2, Pd(NH3)4(OAc)2, Pd(NH3)2(OAc)2,
Pd(OAc)2 in
KOH and/or NMe4OH and/or NaOH, Pd(NH3)4(HCO3)2 and palladium oxalate. Of the
chloride-
containing palladium precursors, Na2PdCl4 is most preferred. Of the chloride
free palladium
precursor salts, the following four are the most preferred: Pd(NH3)4(NO3)2,
Pd(NO3)2,
Pd(NH3)2(NO2)2, Pd(NH3)4(OH)2. Examples of gold salts suitable for use in
precursor solution
include AuC13, HAuC14, NaAuC14, KAuO2, NaAuO2, NMe4AuO2, Au(OAc)3 in KOH
and/or
NMe4OH as well as HAu(N03)4 in nitric acid, with KAuO2 being the most
preferred of the
chloride free gold precursors. Examples of rhodium salts suitable for use in
precursor solutions
include RhC13, Rh(OAc)3, and Rh(N03)2. Similar salts of the above described
third catalytic
components may also be selected.
[0063] Furthermore, more than one salt may be used in a given precursor
solution. For
example, a palladium salt may be combined with a gold salt or two different
palladium salts may
be combined together in a single precursor solution. Precursor solutions
typically may be made
by dissolving the selected salt or salts in water, with or without solubility
modifiers such as acids,
bases or other solvents. Other non-aqueous solvents may also be suitable.
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[0064] The precursor solutions may be impregnated onto the support material
simultaneously
(e.g. co-impregnation) or sequentially and may be impregnated through the use
of one or multiple
precursor solutions. With three or more catalytic components, a combination of
simultaneous
and sequential impregnation may be used. For example, palladium and rhodium
may be
impregnated through the use of a single precursor solution (referred to as a
co-impregnation),
followed by impregnation with a precursor solution of the gold. In addition, a
catalytic
component may be impregnated on to support material in multiple steps, such
that a portion of
the catalytic component is contacted each time. For example, one suitable
protocol may include
impregnating with Pd, followed by impregnating with Au, followed by
impregnating again with
Au.
[0065] The order of impregnating the support material with the precursor
solutions is not
critical; although there may be some advantages to certain orders, as
discussed below, with
respect to the calcining step. Preferably, the palladium catalytic component
is impregnated onto
the support material first, with gold being impregnated after palladium, or
last. Rhodium or other
third catalytic component, when used, may be impregnated with the palladium,
with the gold or
by itself. Also, the support material may be impregnated multiple times with
the same catalytic
component. For example, a portion of the overall gold contained in the
catalyst may be first
contacted, followed by contacting of a second portion of the gold. One more
other steps may
intervene between the steps in which gold is contacted to the support
material, e.g. calcining,
reducing, and/or fixing.
[0066] The acid-base profile of the precursor solutions may influence whether
a co-
impregnation or a sequential impregnation is utilized. Thus, only precursor
solutions with
similar acid-base profile should be used together in a co-impregnating step;
this eliminates any
acid-base reactions that may foul the precursor solutions.
[00671 For the impregnating step, the volume of precursor solution is selected
so that it
corresponds to between about 85% and about 110% of the pore volume of the
support material.
Volumes between about 95% and about 100% of the pore volume of the support
material are
preferred, and more preferably between about 98% and about 99% of the pore
volume.
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[0068] Typically, the precursor solution is added to the support material and
the support
material is allowed absorb the precursor solution. This may be done drop wise
until incipient
wetness of the support material is substantially achieved. Alternatively, the
support material may
be placed by aliquots or batch wise into the precursor solution. A roto-
immersion or other
assistive apparatus may be used to achieve thorough contact between the
support material and the
precursor solution. Further, a spray device may be used such that the
precursor solution is
sprayed through a nozzle onto the support material, where it absorbed.
Optionally, decanting,
heat or reduced pressure may be used to remove any excess liquid not absorbed
by the support
material or to dry the support material after impregnation.
[0069] For the impregnating step, the volume of precursor solution is selected
so that it
corresponds to between about 85% and about 110% of the pore volume of the
support material.
Volumes between about 95% and about 100% of the pore volume of the support
material are
preferred, and more preferably between about 98% and about 99% of the pore
volume.
[0070] Typically, the precursor solution is added to the support material and
the support
material is allowed absorb the precursor solution. This may be done drop wise
until incipient
wetness of the support material is substantially achieved. Alternatively, the
support material may
be placed by aliquots or batch wise into the precursor solution. A roto-
immersion or other
assistive apparatus may be used to achieve thorough contact between the
support material and the
precursor solution. Further, a spray device may be used such that the
precursor solution is
sprayed through a nozzle onto the support material, where it absorbed.
Optionally, decanting,
heat or reduced pressure may be used to remove any excess liquid not absorbed
by the support
material or to dry the support material after impregnation.
[0071) Other contacting techniques may be used to avoid a fixing step while
still achieving a
shell catalyst. For example, catalytic components may be contacted to a
support material through
a chemical vapor deposition process, such as described in US2001/0048970.
Also, spray coating or otherwise layering a uniformly pre-
impregnated support material, as an outer layer, on to an inner layer
effectively forms shell
catalyst that may also be described as a layered support material. In another
technique,
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organometallic precursors of catalytic components, particularly with respect
to gold, may be used
to form shell catalysts, as described in U.S. Patent No. 5,700,753.
[0072] A physical shell formation technique may also be suitable for the
production of shell
catalysts. Here, the precursor solution may be sprayed onto a heated support
material or a
layered support material, where the solvent of the precursor solution
evaporates upon contact
with the heated support material, thus depositing the catalytic components in
a shell on the
support material. Preferably, temperatures between about 40 and 140 C maybe
used. The
thickness of the shell may be controlled by selecting the temperature of the
support material and
the flow rate of the solution through the spray nozzle. For example, with
temperatures above
about 100 C, a relatively thin shell is formed. This embodiment may be
particularly useful when
chloride free precursors are utilized to help enhance the shell formation on
the support material.
[0073] One skilled in the art will understand that a combination of the
contacting steps may
be an appropriate method of forming a contacted support material.
[0074] Fixing SteP
[0075] It may be desirable to transform at least a portion of the catalytic
components on the
contacted support material from a water-soluble form to a water-insoluble
form. Such a step may
be referred to as a fixing step. This may be accomplished by applying a fixing
agent (e.g.
dispersion in a liquid, such as a solution) to the impregnated support
material which causes at
least a portion of the catalytic components to precipitate. This fixing step
helps to form a shell
catalyst, but is not required to form shell catalysts.
[0076] Any suitable fixing agent may be used, with hydroxides (e.g. alkali
metal hydroxides),
silicates, borates, carbonates and bicarbonates in aqueous solutions being
preferred. The
preferred fixing agent is NaOH. Fixing may be accomplished by adding the
fixing agent to the
support material before, during or after the precursor solutions are
impregnated on the support
material. Typically, the fixing agent is used subsequent to the contacting
step such that the
contacted support material is allowed to soak in the fixing agent solution for
about 1 to about 24
hours. The specific time depends upon the combination of the precursor
solution and the fixing
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agent. Like the impregnating step, an assistive device, such as a roto
immersion apparatus as
described in U.S. Patent No. 5,332,710 may
advantageously be used in the fixing step.
[0077] The fixing step may be accomplished in one or multiple steps, referred
as a co-fix or a
separate fix. In a co-fix, one or more volumes of a fixing agent solution is
applied to the
contacted support material after all the relevant precursor solutions have
been contacted to the
support material, whether the contact was accomplished through the use of one
or multiple
precursor solutions. For example, fixing after sequential impregnation with a
palladium
precursor solution, a gold precursor solution and a rhodium precursor solution
would be a co-fix,
as would fixing after a co-impregnation with a palladium/rhodium precursor
solution followed by
impregnation with a gold precursor solution. An example of co-fixing may be
found in U.S.
Patent No. 5,314,888:.
[0078] A separate fix, on the other hand, would include applying a fixing
agent solution
during or after each impregnation with a precursor solution. For example, the
following
protocols would be a separate fix: a) impregnating palladium followed by
fixing followed by
impregnating with gold followed by fixing; or b) co-impregnating with
palladium and rhodium
followed by fixing followed by impregnating with gold followed by fixing.
Between a fix and
subsequent impregnation, any excess liquid may be removed and the support
material dried,
although this is not necessarily the case. An example of separate fixing may
be found in U.S.
Patent No. 6,034,030.
[0079] In another embodiment, the fixing step and the contacting step are
conducted
simultaneously, one example of which is described in U.S. Patent No.
4,048,096..
For example, a simultaneous fix might be: impregnating with
palladium followed by fixing followed by impregnating with gold and fixing
agent. In a
variation on this embodiment, the fix may be conducted twice for a catalytic
component. A
catalytic component may be partially fixed when it is contacted to the support
material (called a
"pre- fix"), followed an additional, final fix. For example: impregnating with
palladium
followed by impregnating with gold and a pre-fixing agent followed by fixing
with a final fixing
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agent. This technique may be used to help insure the formation of shell type
catalyst as opposed
to an all throughout catalyst.
[0080] In another embodiment, particularly suitable for use with chloride free
precursors, the
support material is pre-treated with a fixing agent to adjust the properties
of the support material.
In this embodiment, the support material is first impregnated with either an
acid or base solution,
typically free of metals. After drying, the support material is impregnated
with a precursor
solution that has the opposite acidity/alkalinity as the dried support
material. The ensuing acid-
base reaction forms a shell of catalytic components on the support material.
For example, nitric
acid may be used to pre-treat a support material that in turn is impregnated
with a basic precursor
solution such as Pd(OH)2 or Au(OH)3. This formation technique may be
considered as using a
fixing step followed by a contacting step.
[0081] The concentration of fixing agent in the solution is typically a molar
excess of the
amount of catalytic components impregnated on the support material. The amount
of fixing
agent should be between about 1.0 to about 2.0, preferably about 1.1 to about
1.8 times the
amount necessary to react with the catalytically active cations present in the
water-soluble salt.
In one embodiment using a high Au/Pd atomic or weight ratio, an increased
molar excess of
hydroxide ion enhances the CO2 selectivity and activity of the resultant
catalyst.
[0082] The volume of fixing agent solution supplied generally should be an
amount
sufficient to cover the available free surfaces of the impregnated support
material This may be
accomplished by introducing, for example, a volume that is greater than the
pore volume of the
contacted support material.
[0083] The combination of impregnating and fixing steps can form a shell type
catalyst. But,
the use of halide free precursor solutions also permits the formation of a
shell catalyst while
optionally eliminating the fixing step. In the absence of a chloride
precursor, a washing step, as
discussed below, may be obviated. Further, the process can be free of a step
of fixing catalytic
components that would otherwise be needed to survive the washing step. Because
no washing
step is needed, the catalytic components need not be fixed to survive the
washing step.
Subsequent steps in the method making the catalyst do not require the
catalytic components be
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fixed and thus the remainder of the step maybe carried out without additional
preparatory steps.
Overall, the use of chloride free precursors permits a catalyst or pre-
catalyst production method
that is free of a step of washing, thus reducing the number of steps needed to
produce the catalyst
and eliminating the need to dispose of chloride containing waste.
[0084] Washing Step
[0085] Particularly, when halide containing precursor solutions are utilized
and in other
applications as desired, after the fixing step, the fixed support material may
be washed to remove
any halide residue on the support or otherwise treated to eliminate the
potential negative effect of
a contaminant on the support material. The washing step included rinsing the
fixed support
material in water, preferably deionized water. Washing may be done in a batch
or a continuous
mode. Washing at room temperature should continue until the effluent wash
water has a halide
ion content of less than about 1000 ppm, and more preferably until the final
effluent gives a
negative result to a silver nitrate test. The washing step may be carried out
after or
simultaneously with the reducing step, discussed below, but preferably is
carried out before. As
discussed above, the use of halide free precursor solutions permits the
elimination of the washing
step.
[0086] Calcining Step
[0087] After at least one catalytic component has been contacted to the
support material, a
calcining step may be employed. The calcining step typically is before the
reducing step and
after the fixing step (if such a step is used) but may take place elsewhere in
the process. In
another embodiment, the calcining step is carried out after the reducing step.
The calcining step
includes heating the support material in a non-reducing atmosphere (i.e.
oxidizing or inert).
During calcination, the catalytic components on the support material are at
least partially
decomposed from their salts to a mixture of their oxide and free metal form.
[0088] For example, the calcining step is carried out at a temperature in the
range of about
100 C to about 700 C, preferably between about 200 C and about 500 C. Non-
reducing gases
used for the calcination may included one or more inert or oxidizing gases
such as helium,
nitrogen, argon, neon, nitrogen oxides, oxygen, air, carbon dioxide,
combinations thereof or the
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like. In one embodiment, the calcining step is carried out in an atmosphere of
substantially pure
nitrogen, oxygen, air or combinations thereof. Calcination times may vary but
preferably are
between about 1 and 5 hours. The degree of decomposition of the catalytic
component salts
depends on the temperature used and length of time the impregnated catalyst is
calcined and can
be followed by monitoring volatile decomposition products.
[0089] One or more calcining steps may be used, such that at any point after
at least one
catalytic component is contacted to the support material, it may be calcined.
Preferably, the last
calcining step occurs before contact of the gold catalytic component to a
zirconia support
material. Alternately, calcining of a zirconia support material containing
gold is conducted at
temperatures below about 300 C. By avoiding calcining the gold containing
zirconia support
material at temperatures above about 300 C, the risk that the CO2 selectivity
of the resultant
catalyst will be detrimentally affected is reduced.
[0090] Exemplary protocols including a calcining step include: a) impregnating
with
palladium followed by calcining followed by impregnating with gold; b) co-
impregnating
palladium and rhodium followed by calcining followed by impregnating with Au;
c)
impregnating with palladium followed by calcining followed by impregnating
with rhodium
followed by calcining followed by impregnating with gold; or d) impregnating
with palladium
and rhodium, followed by impregnating with gold, followed by calcination.
[0091] Reducing Step
[0092] Another step employed generally herein to at least partially transform
any remaining
catalytic components from a salt or oxide form to a catalytically active
state, such as by a
reducing step. Typically this is done by exposure of salts or oxides to a
reducing agent, examples
of which include ammonia, carbon monoxide, hydrogen, hydrocarbons, olefins,
aldehydes,
alcohols, hydrazine, primary amines, carboxylic acids, carboxylic acid salts,
carboxylic acid
esters and combinations thereof. Hydrogen, ethylene, propylene, alkaline
hydrazine and alkaline
formaldehyde and combinations thereof are preferred reducing agents with
ethylene and
hydrogen blended with inert gases particularly preferred. Although reduction
employing a
gaseous environment is preferred, a reducing step carried with a liquid
environment may also be
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used (e.g. employing a reducing solution). The temperature selected for the
reduction can range
from ambient up to about 550 C. Reduction times will typically vary from about
1 to about 5
hours.
[0093] Since the process used to reduce the catalytic components may
influences the
characteristics of the final catalyst, conditions employed for the reduction
may be varied
depending on whether high activity, high selectivity or some balance of these
properties is
desired.
[0094] In one embodiment, palladium is contacted to the support material,
fixed and reduced
before gold is contacted and reduced, as described in U.S. Patent Nos.
6,486,093, 6,015,769 and
related patents.
[0095] Exemplary protocols including a reducing step include: a) impregnating
with
palladium followed by optionally calcining followed by impregnating with gold
followed by
reducing; b) co-impregnating with palladium and gold followed by optionally
calcining followed
by reducing; or c) impregnating with palladium followed by optionally
calcining followed by
reducing followed by impregnating with gold.
[0096] Modifying Step
[0097] Usually after the reducing step and before the catalyst is used, a
modifying step is
desirable. While the catalyst may be used with the modifying step, the step
has several beneficial
results, including lengthening the operational life time of the catalyst. The
modifying step is
sometimes called an activating step and may be accomplished in accordance with
conventional
practice. Namely, the reduced support material is contacted with a modifying
agent, such as an
alkali metal carboxylate and/or alkali metal hydroxide, prior to use.
Conventional alkali metal
carboxylates such as the sodium, potassium, lithium and cesium salts of C2-4
aliphatic carboxylic
acids are employed for this purpose. A preferred activating agent in the
production of VA is an
alkali acetate, with potassium acetate (KOAc) being the most preferred.
[0098] The support material may optionally be impregnated with a solution of
the modifying
agent. After drying, the catalyst may contain, for example, about 10 to about
70, preferably about
20 to about 60 grams of modifying agent per liter of catalyst.
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[0099] Methods of Making Alkenyl Alkanoates
[00100] The present invention may be utilized to produce alkenyl alkanoates
from an alkene,
alkanoic acid and an oxygen containing gas in the presence of a catalyst.
Preferred alkene
starting materials contain from two to four carbon atoms (e.g. ethylene,
propylene and n-butene).
Preferred alkanoic acid starting materials used in the process of this
invention for producing
alkenyl alkanoates contain from two to four carbon atoms (e.g., acetic,
propionic and butyric
acid). Preferred products of the process are VA, vinyl propionate, vinyl
butyrate, and allyl
acetate. The most preferred starting materials are ethylene and acetic acid
with the VA being the
most preferred product. Thus, the present invention is useful in the
production of olefinically
unsaturated carboxylic esters from an olefinically unsaturated compound, a
carboxylic acid and
oxygen in the presence of a catalyst. Although the rest of the specification
discusses VA
exclusively, it should be understood that the catalysts, method of making the
catalysts and
production methods are equally applicable to other alkenyl alkanoates, and the
description is not
intended as limiting the application of the invention to VA.
[00101] When VA is produced using the catalyst of the present invention, a
stream of gas,
which contains ethylene, oxygen or air, and acetic acid is passed over the
catalyst. The
composition of the gas stream can be varied within wide limits, taking in
account the zone of
flammability of the effluent. For example, the molar ratio of ethylene to
oxygen can be about
80:20 to about 98:2, the molar ratio of acetic acid to ethylene can be about
100:1 to about 1:100,
preferably about 10:1 to 1:10, and most preferably about 1:1 to about 1:8. The
gas stream may
also contain gaseous alkali metal acetate and/or inert gases, such as
nitrogen, carbon dioxide
and/or saturated hydrocarbons. Reaction temperatures which can be used are
elevated
temperatures, preferably those in the range of about 125-220 C. The pressure
employed can be a
somewhat reduced pressure, normal pressure or elevated pressure, preferably a
pressure of up to
about 20 atmospheres gauge.
[00102] In addition to fixed bed reactors, the methods of producing alkenyl
alkanoates and the
catalyst of the present invention may also be suitably employed in other types
of reaction, for
example, fluidized bed reactors.
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[00103] Examples
[00104] The following examples are provided for illustration only and not
intended to be
limiting. The amounts solvents and reactants are approximate. The Au/Pd atomic
ratio may be
converted to the Au/Pd weight ratio and vice versa by the following equations:
Au/Pd atomic
ratio = 0.54*(Au/Pd weight ratio) and Au/Pd weight ratio = 1.85(Au/Pd atomic
ratio. Reduction
may be abbreviated `R' followed by the temperature in C at which the
reduction was carried out.
Likewise, calcination may be abbreviated `C' followed by the temperature in C
at which the
calcination was carried out, whereas a drying step may be abbreviated as
`dry'.
[00105] The catalyst of examples 1-11 may be prepared as described in the
example and tested
according to the following procedure, where catalyst from Examples 1-7 may be
compared to
each other and catalyst from 8-11 may be compared to each other. Results are
provided where
available.
[00106] The catalysts of the examples were tested for their activity and
selectivity to various
by-products in the production of vinyl acetate by reaction of ethylene, oxygen
and acetic acid. To
accomplish this, about 60 ml of the catalyst prepared as described were placed
in a stainless steel
basket with the temperature capable of being measured by a thermocouple at
both the top and
bottom of the basket. The basket was placed in a Berty continuously stirred
tank reactor of the
recirculating type and was maintained at a temperature which provided about
45% oxygen
conversion with an electric heating mantle. A gas mixture of about 50 normal
liters (measured at
N.T.P.) of ethylene, about 10 normal liters of oxygen, about 49 normal liters
of nitrogen, about
50 g of acetic acid, and about 4 mg of potassium acetate, was caused to travel
under pressure at
about 12 atmospheres through the basket, and the catalyst was aged under these
reaction
conditions for at least 16 hours prior to a two hour run, after which the
reaction was terminated.
Analysis of the products was accomplished by on-line gas chromatographic
analysis combined
with off-line liquid product analysis by condensing the product stream at
about 10 C to obtain
optimum analysis of the end products carbon dioxide (CO2), heavy ends (HE) and
ethyl acetate
(EtOAc), the results of which may be used to calculate the percent
selectivities (CO2 Selectivity)
of these materials for each example. The relative activity of the reaction
expressed as an activity
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factor (Activity) may be computer calculated using a series of equations that
correlates the
activity factor with the catalyst temperature (during the reaction), oxygen
conversion, and a series
of kinetic parameters for the reactions that take place during VA synthesis.
More generally, the
activity factor typically is inversely related to the temperature required to
achieve constant
oxygen conversion.
[00107] Rhodium Catalyst Examples
[00108] Example 1: A support material containing palladium and rhodium metal
was prepared
as follows: The support material in an amount of 250 ml consisting of Sud
Chemie KA-160 silica
spheres having a nominal diameter of 7 mm., a density of about 0.569 g/ml, in
absorptivity of
about 0.568 g H2O/g support, a surface area of about 160 to 175 m2/g, and a
pore volume of
about 0.68 ml/g., was first impregnated by incipient wetness with 82.5 ml of
an aqueous solution
of sodium tetrachloropalladium (II) (Na2PdC14) and rhodium chloride trihydrite
(RhC13.3H2O)
sufficient to provide about 7 grams of elemental palladium and about 0.29
grams of elemental
rhodium per liter of catalyst. The support was shaken in the solution for 5
minutes to ensure
complete absorption of the solution. The palladium and rhodium were then fixed
to the support
as palladium (II) and rhodium (III) hydroxides by contacting the treated
support by ro"to-
immersion for 2.5 hours at approximately 5 rpm with 283 ml of an aqueous
sodium hydroxide
solution prepared from 50% w/w NaOH/H2O in an amount of 120% of that needed to
convert the
palladium and rhodium to their hydroxides. The solution was drained from the
treated support
and the support was then rinsed with deionized water and dried at 100 C in a
fluid bed drier for
1.2 hours. The support material containing palladium and rhodium hydroxides
was then
impregnated with an aqueous solution (81 ml) containing 1.24 g Au from NaAuC14
and 2.71g
50% NaOH solution (1.8 equivalents with respect to Au) using the incipient
wetness method.
The NaOH treated pills were allowed to stand overnight to ensure precipitation
of the Au salt to
the insoluble hydroxide. The pills were thoroughly washed with deionized water
(-5 hours) to
remove chloride ions and subsequently dried at 100 C in a fluid bed drier for
1.2 hours. The
palladium, rhodium, and gold containing support was then calcined at 400 C for
2 hours under
air and then allowed to naturally cool to room temperature. The palladium,
rhodium, and gold
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were reduced by contacting the support with C2H4 (1% in nitrogen) in the vapor
phase at 150 C
for 5 hours. Finally the catalyst was impregnated by incipient wetness with an
aqueous solution
of l Og of potassium acetate in 81 ml H2O and dried in a fluid bed drier at
100 C for 1.2 hours.
[00109] Example 2: A support material utilizing palladium and rhodium
hydroxides was
prepared as described in Example 1. The palladium and rhodium containing
support was then
calcined at 400 C for 2 hours under air and then allowed to naturally cool to
room temperature.
The calcined support material containing palladium and rhodium hydroxides was
then
impregnated with an aqueous solution (81 ml) containing 1.24g Au from NaAuC14
and 2.71g
50% NaOH solution (1.8 equivalents with respect to Au) using the incipient
wetness method.
The NaOH treated pills were allowed to stand overnight to ensure precipitation
of the Au salt to
the insoluble hydroxide. The pills were thoroughly washed with deionized water
(-5 hours) to
remove chloride ions and subsequently dried at 100 C in a fluid bed drier for
1.2 hours. The
palladium, rhodium, and gold were then reduced by contacting the support with
C2H4 (1% in
nitrogen) in the vapor phase at 150 C for 5 hours. Finally the catalyst was
impregnated by
incipient wetness with an aqueous solution of lOg of potassium acetate in 81
ml H2O and dried in
a fluid bed drier at 100 C for 1.2 hours.
[00110] Example 3: A support material containing palladium and rhodium
hydroxides was
prepared as described in Example 1. The palladium and rhodium containing
support was then
calcined at 400 C for 2 hours under air and then allowed to naturally cool to
room temperature.
The calcined support material containing palladium and rhodium hydroxides was
then reduced by
contacting the support with C2H4 (1% in nitrogen) in the vapor phase at 150 C
for 5 hours. The
support containing palladium and rhodium metal was subsequently impregnated
with an aqueous
solution (81 ml) containing 1.24g Au from NaAuC14 and 2.71g 50% NaOH solution
(1.8
equivalents with respect to Au) using the incipient wetness method. The NaOH
treated pills
were allowed to stand overnight to ensure precipitation of the Au salt to the
insoluble hydroxide.
The pills were thoroughly washed with deionized water (-5 hours) to remove
chloride ions and
subsequently dried at 100 C in a fluid bed drier for 1.2 hours. The palladium,
rhodium, and gold
were then reduced by contacting the support with C2H4 (1% in nitrogen) in the
vapor phase at
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150 C for 5 hours. Finally the catalyst was impregnated by incipient wetness
with an aqueous
solution of lOg of potassium acetate in 81 ml H2O and dried in a fluid bed
drier at 100 C for 1.2
hours.
[00111] Example 4: A support material containing palladium and rhodium
hydroxides was
prepared as described in Example 1. The palladium and rhodium containing
support was then
calcined at 400 C for 2 hours under air and then allowed to naturally cool to
room temperature.
The calcined support material containing palladium and rhodium hydroxides was
then reduced by
contacting the support with C2H4 (1% in nitrogen) in the vapor phase at 150 C
for 5 hours. The
support containing palladium and rhodium metal was subsequently impregnated
with an aqueous
solution (81 ml) containing 1.lg Au from KAuO2 using the incipient wetness
method. The pills
were subsequently dried at 100 C in a fluid bed drier for 1.2 hours. The
palladium, rhodium, and
gold were then reduced by contacting the support with C2H4 (1% in nitrogen) in
the vapor phase
at 150 C for 5 hours. Finally the catalyst was impregnated by incipient
wetness with an aqueous
solution of lOg of potassium acetate in 81 ml H2O and dried in a fluid bed
drier at 100 C for 1.2
hours.
[00112] Example 5: A support material containing palladium and rhodium
hydroxides was
prepared as described in Example 1. The palladium and rhodium containing
support was then
calcined at 400 C for 2 hours under air and then allowed to naturally cool to
room temperature.
The calcined support containing palladium and rhodium hydroxides was
subsequently
impregnated with an aqueous solution (81 ml) containing 1. 1g Au from KAuO2
using the
incipient wetness method. The pills were then dried at 100 C in a fluid bed
drier for 1.2 hours.
The palladium, rhodium, and gold were then reduced by contacting the support
with C2H4 (1% in
nitrogen) in the vapor phase at 150 C for 5 hours. Finally the catalyst was
impregnated by
incipient wetness with an aqueous solution of lOg of potassium acetate in 81
ml H2O and dried in
a fluid bed drier at 100 C for 1.2 hours.
[00113] Example 6: A support material containing palladium and rhodium
hydroxides was
prepared as described in Example 1. The palladium and rhodium containing
support was then
calcined at 400 C for 2 hours under air and then allowed to naturally cool to
room temperature.
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The calcined support material containing palladium and rhodium hydroxides was
then reduced by
contacting the support with C2H4 (1% in nitrogen) in the vapor phase at 150 C
for 5 hours. The
support containing palladium and rhodium metal was subsequently impregnated
with an aqueous
solution (81 ml) containing 1.1g Au from KAuO2 and 10g potassium acetate using
the incipient
wetness method. The pills were subsequently dried at 100 C in a fluid bed
drier for 1.2 hours.
[00114] Example 7 (Reference Catalyst): A support material containing
palladium metal was
prepared as follows: The support material in an amount of 250 ml consisting of
Sud Chemie KA-
160 silica spheres having a nominal diameter of 7 mm., a density of about
0.569 g/rri, in
absorptivity of about 0.568 g H20/g support, a surface area of about 160 to
175 m2/g, and a pore
volume of about 0.68 ml/g., was first impregnated by incipient wetness with
82.5 mi of an
aqueous solution of sodium tetrachloropalladium (II) (Na2PdC14) sufficient to
provide about 7
grams of elemental palladium per liter of catalyst. The support was shaken in
the solution for 5
minutes to ensure complete absorption of the solution. The palladium was then
fixed to the
support as palladium (II) hydroxides by contacting the treated support by roto-
immersion for 2.5
hours at approximately 5 rpm with 283 ml of an aqueous sodium hydroxide
solution prepared
from 50% w/w NaOH/H20 in an amount of 110% of that needed to convert the
palladium to its
hydroxide. The solution was drained from the treated support and the support
was then rinsed
with deionized water and dried at 100 C in a fluid bed drier for 1.2 hours.
The support material
containing palladium hydroxide was then impregnated with an aqueous solution
(81 ml)
containing 1.24 g Au from NaAuC14 and 2.71g 50% NaOH solution (1.8 equivalents
with respect
to Au) using the incipient wetness method. The NaOH treated pills were allowed
to stand
overnight to ensure precipitation of the Au salt to the insoluble hydroxide.
The pills were
thoroughly washed with deionized water (-5 hours) to remove chloride ions and
subsequently
dried at 100 C in a fluid bed drier for 1.2 hours. The palladium and gold
containing support was
then reduced by contacting the support with C2H4 (1% in nitrogen) in the vapor
phase at 150 C
for 5 hours. Finally the catalyst was impregnated by incipient wetness with an
aqueous solution
of l Og of potassium acetate in 81 ml H2O and dried in a fluid bed drier at
100 C for 1.2 hours.
Table 1 shows comparison CO2 selectivity and activity for the catalyst of
Examples, 1 and 7.
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[00115] Table 1
CO2 Selectivity Activity
Example 1 9.89 2.32
Example 7 (Reference Catalyst) 11.13 2.36
[00116] Layered Support Examples
[00117] Example 8: 40 g of Zr02 (RC-100, supplied by DKK) was calcined at 650
C for 3 h.
Resulting material has a BET surface area 38 m2/g. The material was ball
milled with 120 ml of
DI water for 6 h. The sol was mixed with 22.5 g of the binder zirconium
acetate supplied by
DKK (ZA-20) and sprayed onto 55 g of spheres of bentonite KA-160 with OD-
7.5mm. Coated
beads were calcined for 3 h at 600 C. Examination under microscope has shown
uniform shell
formation with thickness of 250 m.
[00118] Example 9: 20 g of Zr02 (XZ16075, BET surface area 55 m2/g) were
impregnated
with Pd(N03)2 solution (Aldrich) to give Pd loading of 39 mg/g of Zr02.
Impregnated material
was dried and calcined at 450 C for 4 h. The material was ball milled with 60
ml of DI water for
4h, mixed with 11 g of a binder (ZA-20) and sprayed onto 30 g of bentonite KA-
160 spheres.
The beads were calcined at 450 C for 3h. This procedure results in formation
of a strong uniform
shell with 160 gm thickness.
[00119] Example 10: The beads from Example 8 were impregnated with solution of
potassium
acetate to give loading of 40 mg KOAc/ml of KA-160, dried and calcined at 300
C for 4 h. After
that the solution, containing 9.4 mM of Pd(from Pd(NH3)4(OH)2 supplied by
Heraeus) and 4.7
mM of Au (from a 1 M solution, Au(OH)3 "Alfa" dissolved in 1.6 M KOH) was
sprayed onto
these beads. Material was reduced with the mixture: 5% H2, 95 % N2 at 200 C
for 4 h. The beads
were crushed and tested in fix bed micro reactor under conditions described in
the experimental
section. CO2 selectivity of - 6% at 45% oxygen conversion was achieved.
[00120] Example 11 (reference catalyst): The same catalyst prepared in Example
7 was used
as a reference catalyst here. Table 2 shows comparison CO2 selectivity and
activity for the
catalyst of Examples 9-11.
[00121] Table 2
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CO2 Selectivity Activity
Example 9 9.33 2.08
Example 10 9.03 1.69
Example 11 (Reference Catalyst) 11.13 2.36
[00122] Zirconia Support Material and Chloride Free Precursor Examples
[00123] The following general procedure was used for this set of examples.
Zirconia support
material catalysts were made as follows: various shaped catalyst carriers were
crushed and
sieved. Zirconia support materials were supplied by NorPro (XZ16052 and
XZ16075), DKK and
MEI. Silica support materials were supplied by Degussa and Sud Chemie. The
sieve fraction of
180-425um was impregnated (either simultaneously or sequentially with an
intermediate drying
step at 110 C and optionally with an intermediate calcination step) to
incipient wetness with a Pd
and Au precursor solution, optionally calcined in air, reduced with 5%H2/N2
formation gas, post-
impregnated with KOAc solution, dried at 100 C under N2, and screened in a 8x6
multi channel
fixed bed reactor. A solution of Au(OH)3 in KOH was used as the Au precursor.
Aqueous
solutions of Pd(NH3)4(OH)2, Pd(NH3)2(NO2)2, Pd(NH3)4(NO3)2 and Pd(N03)2 were
used as the
Pd precursors.
[00124] A silica support material catalyst reference was made as follows: A
support material
containing palladium and rhodium metal was prepared as follows: The support
material in an
amount of 250 ml consisting of Sud Chemie KA-160 silica spheres having a
nominal diameter of
7 mm, a density of about 0.569 g/ml, an absorptivity of about 0.568 g H20/g
support, a surface
area of about 160 to 175 m2/g, and a pore volume of about 0.68 mug., was first
impregnated by
incipient wetness with 82.5 ml of an aqueous solution of sodium
tetrachloropalladium (II)
(Na2PdC14) sufficient to provide about 7 grams of elemental palladium per
liter of catalyst. The
support was shaken in the solution for 5 minutes to ensure complete absorption
of the solution.
The palladium was then fixed to the support as palladium(II) hydroxides by
contacting the treated
support by roto-immersion for 2.5 hours at approximately 5 rpm with 283 ml of
an aqueous
sodium hydroxide solution prepared from 50% w/w NaOH/H2O in an amount of 110%
of that
needed to convert the palladium to its hydroxide. The solution was drained
from the treated
support and the support was then rinsed with deionized water and dried at 100
C in a fluid bed
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drier for 1.2 hours. The support material containing palladium hydroxide was
then impregnated
with an aqueous solution (81 ml) containing 1.24 g Au from NaAuC14 and 2.71g
50% NaOH
solution (1.8 equivalents with respect to Au) using the incipient wetness
method. The NaOH
treated pills were allowed to stand overnight to ensure precipitation of the
Au salt to the insoluble
hydroxide. The pills were thoroughly washed with deionized water (-5 hours) to
remove
chloride ions. and subsequently dried at 100 C in a fluid bed drier for 1.2
hours. The palladium
and gold containing support was then reduced by contacting the support with
C2H4 (1% in
nitrogen) in the vapor phase at 150 C for 5 hours. Finally the catalyst was
impregnated by
incipient wetness with an aqueous solution of lOg of potassium acetate in 81
ml H2O and dried in
a fluid bed drier at 100 C for 1.2 hours. Before testing, the catalyst was
crushed and sieved. The
sieved fraction in the size range of 180-425um was used.
[00125] Catalyst libraries of arrays of 8 rows x 6 columns in glass vials were
designed and a
rack of 36 glass vials was mounted on a vortexer and agitated while dispensing
metal precursor
solutions using CavroTM liquid dispensing robots. 0.4m1 of support was used
for each library
element, for the glass vial synthesis as well as loaded to each reactor
vessel.
[00126] KOAc loading is reported as grams KOAc per liter catalyst volume or as
mol KOAc
on 0.4m1 support. For the specification of Au loading, the relative atomic
ratio of Au to Pd is
reported as Au/Pd. Pd loading is specified as mg Pd per 0.4ml support volume
(i.e. absolute
amount of Pd in reactor vessel). 1
[00127] The screening protocol used a temperature ramp from 145 C to 165 C in
5 C
increments, at a fixed space velocity of 175% (with 1.5mg Pd on 0.4m1
support). 100% space
velocity is defined as the following flows: 5.75 stem of Nitrogen, 0.94 stem
of Oxygen, 5.94
seem of Ethylene, and 5.38 microliters per minute of Acetic Acid through each
of the 48 catalyst
vessels (all of which had an inner diameter of approximately 4 mm). CO2
selectivity was plotted
versus oxygen conversion, a linear fit performed, and the calculated
(interpolated in most cases)
CO2 selectivity at 45% oxygen conversion reported in the performance summary
tables below.
The temperature at 45% oxygen conversion calculated from the T ramp (linear
fits of CO2
selectivity and oxygen conversion versus reaction temperature is also
reported). The lower this
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calculated temperature the higher the activity of the catalyst. The space time
yield (STY; g VA
produced per ml catalyst volume per h) at 45% oxygen conversion is a measure
of the
productivity of the catalyst.
[00128] Example 12: 400u1 of Zr02 carriers XZ16075 (55m2/g as supplied) and
XZ16052
(precalcined at 650 C/2h to lower the surface area to 42m2/g) were impregnated
with 3 different
Pd solutions to incipient wetness, dried at 110 C for 5h, impregnated with
KAuO2 (0.97M Au
stock solution) to incipient wetness, dried at 110 C for 5h, reduced at 350 C
for 4h in 5%H2/N2
formation gas, post-impregnated with KOAc and dried at 110 C for 5h. The
Pd/Au/Zr02 samples
(shells) were then diluted 1/9.3 with KA160 diluter (preloaded with 40g/1
KOAc), i.e. 43ul
Pd/Au/ZrO2 shell and 357ul diluter (400u1 total fixed bed volume) were charged
to the reactor
vessels. The Pd loading was 14 mg Pd in 400u1 Zr02 shell (or
14*43/400=14/9.3=1.5mg Pd in
reactor vessel for all library elements. The Pd precursors were Pd(NH3)2(NO2)2
in columns 1 and
4, Pd(NH3)4(OH)2 in columns 2 and 5, Pd(NH3)4(NO3)2 in columns 3 and 6.
Au/Pd=0.3 in row 2
and row 5, Au/Pd=0.6 in row 3, Au/Pd=0.9 in row 4, row 6 and row 7. The KOAc
loading was
114umol in rows 2, 3, 5 and 147umol in rows 4, 6, 7. The silica reference
catalyst was loaded
into Row 1. The library was screened using the T ramp screening protocol at
fixed SV.
Screening results are summarized in Table 3
[00129] Table 3
CO,2 Selectivity Temp at STY
Cl Precursors on Si02 7.37 156.6 729
Pd(NH4)2(OH)2 on ZrO2 5.79 152.4 787
Pd(NH3)4(NO3)2 on ZrO2 5.90 152.3 783
Pd(NH3)z(NO2)2 on ZrO2 5.57 150.7 795
*Data shown is taken from average of two Au/Pd atomic ratios (namely 0.3 and
0.6) and two
different Zr02 supports.
[00130] Example 13: 400u1 of Zr02 carriers XZ16075 (55m2/g as supplied) and
XZ16052
(precalcined at 650 C/2h to lower the surface area to 42m2/g) were impregnated
with
Pd(NH3)4(OH)2 (1.117M Pd stock solution) to incipient wetness, calcined at 350
C for 4h in air,
impregnated with KAuO2 (0.97M Au stock solution) to incipient wetness, dried
at 110 C for 5h,
reduced at 350 C for 4h in 5%H2/N2 formation gas, post-impregnated with KOAc
and dried at
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110 C for 5h. The Pd/Au/ZrO2 samples (shells) were then diluted 1/12 with
KA160 diluter
(preloaded with 40g/l KOAc), i.e. 33.3ul Pd/Au/ZrO2 catalyst and 366.7ul
diluter (400ul total
fixed bed volume) were charged to the reactor vessels. The library design and
library element
compositions were as follows: Zr02 XZ16075 in columns 1-3 (left half of
library) and Zr02
XZ16052 (650 C) in columns 4-6 (right half of library). The Pd loading was 18
mg Pd in 400ul
Zr02 shell (or 18*33/400=18/12 mg Pd in reactor vessel) in cell G2, column 3
(cells B3-G3), cell
G5, column 6 (cells B6-G6); 10 mg Pd in 400u1 Zr02 shell (or 10*33/400=10/12
mg Pd in
reactor vessel) in column 1 (cells Al-Gl) and column 4 (cells A4-G4); 14 mg Pd
in 400ul Zr02
shell (or 14*33/400=14/12 mg Pd in reactor vessel) in column 2 (cells. B2-F2)
and column 5
(cells B5-F5). Au/Pd=0.3 in row 2 and row 5, Au/Pd=0.5 in row 3 and row 6,
Au/Pd=0.7 in row
4 and row 7 (except cells Al, A4, G2, G5 where Au/Pd was 0.3). The KOAc
loading was
114umol (except cells D3, G3, D6, G6 where KOAc loading was 147umol). The
silica reference
catalyst was loaded into Row 1. The library was screened using the T ramp
screening protocol at
fixed SV. Screening results are summarized in Table 4.
[00131] Table 4
CO2 Selectivity Temp at 45% Conv STY
Au/Pd Atomic Ratio 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7
Cl Precursors on Si02 6.98 - - 154.8 - - 742.8 - -
Zr02: XZ16052 6.06 5.31 5.38 153.7 152.3 154.9 776.8 806.0 803.0
Zr02: XZ16075 6.18 5.62 5.71 147.5 151.0 154.4 773.8 791.6 790.3
[00132] Example 14: Zr02 carrier (supplied by NorPro, XZ16075, sieve fraction
180-425um,
density 1.15g/ml, pore volume 475ul/g, BET surface area 55m2/g) was
impregnated with
Pd(N03)2 precursor solution to incipient wetness, dried at 110 C, calcined at
250 C (columns 1-
2), 350 C (columns 3-4), 450 C (columns 5-6) in air, impregnated with KAuO2
solution
(prepared by dissolution of Au(OH)3 in KOH), dried at 110 C, reduced with
5%H2/N2 formation
gas at 350 C for 4h, and post-impregnated with KOAc solution. The library has
a KOAc gradient
from 25 to 50g/l in row 2 to row 7. The Pd loading amounts to 1.5mg Pd on
0.4m1 support. Two
different Au loadings were chosen (Au/Pd=0.5 in columns 1, 3, 5 and Au/Pd=0.7
in columns 2,
4, 6). The silica reference catalyst was loaded in row 1. The library was
screened using the T
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ramp screening protocol in MCFB48 VA reactor at fixed SV. Screening results
are summarized
in Table 5.
[001331 Table 5
CO2 Selectivity Temp at 45% Conv STY
Cl Precursors on Si02 7.21 154.7 734
Pd(N03)2 on Zr02 6.10 145.3 775
*Data shown is taken from average of two Au/Pd atomic ratios (namely 0.5 and
0.7) at 40g/L
KOAc, calcination at 450 C, and reduction at 350 C.
[001341 Example 15: Zr02 carrier (supplied by NorPro, XZ16075, sieve fraction
180-425um,
density 1.15g/ml, pore volume 575u1/g, BET surface area 55m2/g) was
impregnated with
Pd(N03)2 precursor solution to incipient wetness, dried at 110 C, calcined at
450 C in air,
impregnated with KAuO2 solution (prepared by dissolution of Au(OH)3 in KOH),
dried at
110 C, reduced with 5%H2/N2 formation gas at 200 C (columns 1-2), 300 C
(columns 3-4), or
400 C (columns 5-6), and post-impregnated with KOAc solution. The library has
a KOAc
gradient from 15 to 40g/l in row 2 to row 7. The Pd loading amounts to 1.5mg
Pd on 0.4m1
support. Two different Au loadings were chosen (Au/Pd=0.5 in columns 1, 3, 5
and Au/Pd=0.7
in columns 2, 4, 6). The silica reference catalyst was loaded in row 1. The
library was screened
in MCFB48 VA reactor using the T ramp screening protocol at fixed SV.
Screening results are
summarized in Table 6.
[00135] Table 6
CO2 Selectivity Tem at 45% Conv STY
Cl Precursors on Si02 7.11 154.2 738
Pd(N03)2 on Zr02 5.51 145.4 797
*Data shown is taken from average of two Au/Pd atomic ratios (namely 0.5 and
0.7) at 40g/L
KOAc, calcination at 450 C, and reduction at 400 C.
[00136] It will be further appreciated that functions or structures of a
plurality of components
or steps may be combined into a single component or step, or the functions or
structures of one
step or component may be split among plural steps or components. The present
invention
contemplates all of these combinations. Unless stated otherwise, dimensions
and geometries of
the various structures depicted herein are not intended to be restrictive of
the invention, and other
34
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53029-5
dimensions or geometries are possible. Plural structural components or steps
can be provided by
a single integrated structure or step. Alternatively, a single integrated
structure or step might be
divided into separate plural components or steps. In addition, while a feature
of the present
invention may have been described in the context of only one of the
illustrated embodiments,
such feature may be combined with one or more other features of other
embodiments, for any
given application. It will also be appreciated from the above that the
fabrication of the unique
structures herein and the operation thereof also constitute methods in
accordance with the present
invention.
[00137] The explanations and illustrations presented herein are intended to
acquaint others
skilled in the art with the invention, its principles, and its practical
application. Those skilled in
the art may adapt and apply the invention in its numerous forms, as may be
best suited to the
requirements of a particular use. Accordingly, the specific embodiments of the
present invention
as set forth are not intended as being exhaustive or limiting of the
invention. The scope of the
invention should, therefore, be determined not with reference to the above
description, but should
instead be determined with reference to the appended claims, along with the
full scope of
equivalents to which such claims are entitled.
