U.S. patent application number 14/069514 was filed with the patent office on 2015-05-07 for method of synthesizing bulk transition metal carbide, nitride and phosphide catalysts.
The applicant listed for this patent is UT-Battelle LLC. Invention is credited to Beth L. Armstrong, Jae Soon Choi, Viviane Schwartz.
Application Number | 20150125378 14/069514 |
Document ID | / |
Family ID | 52822526 |
Filed Date | 2015-05-07 |
United States Patent
Application |
20150125378 |
Kind Code |
A1 |
Choi; Jae Soon ; et
al. |
May 7, 2015 |
METHOD OF SYNTHESIZING BULK TRANSITION METAL CARBIDE, NITRIDE AND
PHOSPHIDE CATALYSTS
Abstract
A method for synthesizing catalyst beads of bulk transmission
metal carbides, nitrides and phosphides is provided. The method
includes providing an aqueous suspension of transition metal oxide
particles in a gel forming base, dropping the suspension into an
aqueous solution to form a gel bead matrix, heating the bead to
remove the binder, and carburizing, nitriding or phosphiding the
bead to form a transition metal carbide, nitride, or phosphide
catalyst bead. The method can be tuned for control of porosity,
mechanical strength, and dopant content of the beads. The produced
catalyst beads are catalytically active, mechanically robust, and
suitable for packed-bed reactor applications. The produced catalyst
beads are suitable for biomass conversion, petrochemistry,
petroleum refining, electrocatalysis, and other applications.
Inventors: |
Choi; Jae Soon; (Knoxville,
TN) ; Armstrong; Beth L.; (Clinton, TN) ;
Schwartz; Viviane; (Knoxville, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UT-Battelle LLC |
Oak Ridge |
TN |
US |
|
|
Family ID: |
52822526 |
Appl. No.: |
14/069514 |
Filed: |
November 1, 2013 |
Current U.S.
Class: |
423/440 ;
423/439 |
Current CPC
Class: |
B01J 37/08 20130101;
B01J 27/14 20130101; B01J 27/188 20130101; B01J 27/22 20130101;
B01J 27/20 20130101; B01J 27/19 20130101; B01J 37/0018 20130101;
B01J 27/24 20130101; B01J 35/002 20130101 |
Class at
Publication: |
423/440 ;
423/439 |
International
Class: |
B01J 27/22 20060101
B01J027/22 |
Goverment Interests
[0001] This invention was made with government support under
Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1. A method of making a catalyst bead comprising: providing an
aqueous suspension of transition metal oxide particles in a
gel-forming base having a binder; dropping the suspension into an
aqueous salt solution to form a gel bead matrix having therein a
dispersion of metal oxide particles; heat-treating the gel bead
matrix to remove the binder and strengthen the gel bead matrix; and
forming at least one of a transition metal carbide bead, a
transition metal nitride bead, and a transition metal phosphide
catalyst bead by carburizing, nitriding, or phosphiding the gel
bead matrix, respectively.
2. The method according to claim 1 wherein the transition metal
oxide particles are selected from the group consisting of
molybdenum oxide, tungsten oxide, niobium oxide and mixtures
thereof.
3. The method according to claim 1 wherein the gel-forming base
includes at least one of sodium alginate, pectin, xanthan gum,
carrageenan and gellan.
4. The method according to claim 1 wherein the aqueous salt
solution includes at least one of CaCl.sub.2, CoCl.sub.2,
NiCl.sub.2, and CuCl.sub.2.
5. The method according to claim 1 wherein the aqueous salt
solution comprises divalent metal salts.
6. The method according to claim 1 wherein the aqueous salt
solution comprises monovalent metal salts.
7. The method according to claim 1 wherein carburizing, nitriding
or phosphiding the gel bead matrix includes ramping the temperature
of the gel bead matrix in the presence of a carburizing gas, a
nitriding gas, or a phosphiding gas.
8. The method according to claim 1 wherein carburizing, nitriding
or phosphiding the gel bead matrix includes incrementally raising
the temperature of the gel bead matrix in the presence of a
carburizing gas, a nitriding gas, or a phosphiding gas.
9. The method according to claim 1 further including rinsing the
gel bead matrix in deionized water and drying the gel bead matrix
substantially at room temperature.
10. A method of making a catalyst bead comprising: suspending a
metal oxide powder in a binder solution of sodium alginate to form
an oxide slurry; dropping the oxide slurry in an aqueous solution
including at least one of calcium chloride, cobalt chloride, nickel
chloride and copper chloride to form a prepared oxide bead;
removing the prepared oxide bead from the aqueous solution and
heating the prepared oxide bead to remove at least a portion of the
binder and strengthen the prepared oxide bead; and activating the
prepared oxide bead in the presence of at least one of carbon,
nitrogen, and phosphor to form a transition metal catalyst
bead.
11. The method according to claim 10 wherein activating the
prepared oxide bead includes heating the prepared oxide bead under
a flow of a reducing gas and a carbon source
12. The method according to claim 10 wherein activating the
prepared oxide bead includes heating the prepared oxide bead under
a flow of a reducing gas and a nitrogen source.
13. The method according to claim 10 wherein activating the
prepared oxide bead includes heating the prepared oxide bead under
a reducing gas and a phosphorus source.
14. The method according to claim 10 wherein removing the prepared
oxide bead from the aqueous solution includes rinsing the prepared
oxide bead in deionized water and drying the prepared oxide bead
substantially at room temperature.
15. The method according to claim 10 wherein activating the
prepared oxide bead includes linearly increasing the temperature of
the prepared oxide bead.
16. The method according to claim 10 wherein activating the
prepared oxide bead includes incrementally raising the temperature
of the prepared oxide bead.
17. A method of making a transition metal catalyst comprising:
providing an aqueous suspension of transition metal oxide particles
in a gel-forming base; submerging the aqueous suspension within an
aqueous solution including at least one of calcium chloride, cobalt
chloride, nickel chloride and copper chloride to form a prepared
oxide bead having therein a dispersion of metal oxide particles;
removing the prepared oxide bead from the aqueous solution and
rinsing the prepared oxide bead to remove at least a portion of the
binder; heat-treating the prepared oxide bead to remove the binder
and strengthen the prepared oxide bead; and inserting the prepared
oxide bead in a temperature-programmed reactor with a flow of a gas
selected from the group consisting of a carburizing gas, a
nitriding gas, and a phosphiding gas and increasing the temperature
of the reactor to convert the metal oxide particles into metal
carbides, metal nitrides, or metal phosphides, respectively.
18. The method according to claim 17 wherein the gel-forming base
includes sodium alginate.
19. The method according to claim 17 wherein increasing the
temperature of the reactor includes linearly increasing the
temperature of the reactor.
20. The method according to claim 17 wherein increasing the
temperature of the reactor includes incrementally raising the
temperature of the reactor.
21. The method according to claim 17 further including drying the
prepared oxide bead substantially at room temperature.
22. The method according to claim 17 wherein the aqueous suspension
includes a catalyst dopant.
23. The method according to claim 22 wherein the catalyst dopant
includes phosphorus.
24. A method of making a transition metal catalyst comprising:
providing an aqueous suspension of transition metal oxide particles
in a gel-forming base; dropping the suspension into an aqueous
solution at a specific pH to form a prepared oxide bead therein
including a dispersion of metal oxide particles; removing the
prepared oxide bead from the aqueous solution and rinsing the
prepared oxide bead to remove at least a portion of the binder;
heat-treating the prepared oxide bead to remove the binder and
strengthen the prepared oxide bead; and forming at least one of a
transition metal carbide bead, a transition metal nitride bead, and
a transition metal phosphide catalyst bead by carburizing,
nitriding, or phosphiding the prepared oxide bead,
respectively.
25. The method according to claim 24 wherein the gel-forming base
includes chitin.
26. The method according to claim 24 wherein the gel-forming base
includes chitosan.
Description
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method of synthesizing
bulk transition metal catalysts.
[0003] Carbides of transition metals such as Ti, Zr, V, Nb, Ta, Cr,
Mo and W, along with their nitride and phosphide counterparts, have
been recognized as catalytically active materials which could
replace or substitute for existing process catalysts due to either
better economics or performance. Potential applications include
petroleum refining and biomass conversion. For example, research
has shown that transition metal carbides, nitrides and phosphides
can exhibit precious-metal-like catalytic behavior in a range of
hydrocarbon conversion reactions such as hydrogenation,
hydrogenolysis, and isomerization. Furthermore, under certain
conditions, these materials compare favorably with CoMo or NiMo
sulfides, which are a workhorse of the current petroleum refining
as catalysts for hydrotreating processes which remove S, N, and 0
impurities from petroleum feedstock.
[0004] In most state-of-the-art catalysts used in petroleum
refining and in the petrochemical industry, the active catalytic
components or phases are finely dispersed on high surface area
supports, for instance alumina and zeolites, to maximize the
specific surface area (e.g., m.sup.2/g) of the active component.
Supports are typically shaped as pellets or beads before deposition
of catalytically active components. This shaping of powders into
beads and pellets is necessary for practical catalytic processes
which are generally implemented in large-scale fixed bed reactors.
In fact, charging a large amount of catalyst powders in a reactor
will lead to a densely packed bed, causing an excessive pressure
drop and other technical issues.
[0005] In certain applications, deploying catalytic materials
without supports (i.e., use as bulk catalysts) could be more
advantageous. For example, having bulk catalysts could mitigate
undesired reactions which involve support sites and/or interfaces
between supports and active phases, thereby minimizing the
formation of unwanted byproducts or deactivation species. The bulk
catalysts could be particularly interesting in the emerging field
of catalytic processing of biomass-derived liquids such as
pyrolysis oils (also known as bio-oils), as conventional support
materials and/or interfaces between supports and active phases are
not structurally stable under the hot water-rich environments
involved.
[0006] It has been recently shown that bulk transition metal
carbides, nitrides and phosphides can be prepared with high surface
areas via a temperature programmed reaction. In this procedure, by
increasing the reaction temperature slowly and in a controlled
manner in a flow of reducing gas mixture (e.g., CH.sub.4/H.sub.2 in
the case of carburization), transition metal oxides are transformed
to high surface area carbides, nitrides and phosphides. These
materials are therefore an attractive candidate as bulk catalysts
if they can be prepared in shapes adequate for practical
applications (e.g., beads, pellets). Metal carbides are hard and
refractory materials, which makes it difficult to shape carbides
without losing attractive catalytic properties such as surface area
(e.g., by high temperature sintering). There has been no known
industrial application of shaped bulk carbide, nitride, or
phosphide catalysts, but some methods have been proposed which
involve activation of extruded metal oxide precursors (e.g.,
carburization or nitridation of Nb, Mo, W oxides). These prior art
processes involve multiple steps to obtain bulk carbide and nitride
pellets. First, acid forms of transition metals need to be
prepared. The prepared metal acid powders are then mixed with
celluloses, and the resulting mixture is peptized. The peptized
product is extruded with an extruder. Following thermal treatments
transform the transition metal acids to oxides, burn out cellulose,
and increase mechanical strength of pellets. The temperature
programmed carburization or nitridation of the pellets leads to
high surface area bulk carbides and nitrides. So far the
application of these prior-art processes has been limited to Mo, W,
and Nb carbides and nitrides.
SUMMARY OF THE INVENTION
[0007] A method for synthesizing beads (or pellets) of bulk
transition metal carbides, nitrides and phosphides is provided. The
method includes providing a water-based slurry including transition
metal oxide particles and binders, dropping or pipetting the oxide
slurry into a salt solution to form oxide beads having a dispersion
of metal oxide particles, rinsing and drying the prepared oxide
beads, heat treating first in air to remove the binder and
strengthen the bead, and subsequently heat treating the prepared
oxide beads in a carburizing gas, a nitriding gas, or a phosphiding
gas to form transition metal catalyst beads. The resulting
transition metal catalyst beads are catalytically active,
mechanically robust, and suitable for packed-bed reactor
applications. The transition metal catalyst beads are suitable for
biomass conversion, petrochemistry, petroleum refining,
electrocatalysis, and other applications.
[0008] In one embodiment, the method includes suspending a
transition metal oxide powder in a solution of sodium alginate to
form a slurry. The slurry is dropped in an aqueous solution
including calcium chloride, cobalt chloride, nickel chloride,
copper chloride, or other metal chlorides to form a prepared oxide
bead. The prepared oxide bead is separated from the aqueous
solution, rinsed, and dried. The prepared oxide bead is then heat
treated in air to remove the binder and strengthen the bead and
subsequently in a temperature programmed reaction in the presence
of a carburizing gas to form a transition metal carbide bead.
[0009] In another embodiment, the prepared oxide bead is heat
treated in the presence of a nitriding gas to form a transition
metal nitride bead. In still another embodiment, the prepared oxide
bead is heat treated in the presence of a phosphiding gas to form a
transition metal phosphide bead. Variables that control the bead
size, bead porosity, and bead mechanical strength include the
concentration of the alginate, the molecular weight of the
alginate, the concentration of the chloride solution, the time the
beads are submerged in the chloride solution, the heat treating
conditions, and the amount of metal oxide powder. The method of the
present invention is suitable for essentially any transition metal
oxide, including for example MoO.sub.3, Nb.sub.2O.sub.5, and
WO.sub.3. Physical mixtures of different metal oxides can also be
used to form oxide beads.
[0010] The present invention therefore provides a water-based
method to synthesize beads of essentially any kind of bulk
transition metal oxide without needing a metal acid synthesis or an
extrusion step. In addition to the sodium alginate binders and
metal chloride salts mentioned above, any ionic gelling
polysaccharides/divalent salt combinations should work for gelling
(or bead formation) processes. Examples of polysaccharides include
pectin, xanthan gum, carrageenan and gellan (monovalent cations
work best with carrageenan and gellan). Chitin or chitosan can also
be used, but instead of a salt, one needs to use pH changes to
drive gelling processes.
[0011] Activation (e.g., carburization, nitridation, phosphidation)
of prepared oxide beads leads to bulk carbide, nitride, and
phosphide catalyst beads with good catalytic performance and
mechanical strength. In addition to the broad applicability of the
present method, the method allows control of bead porosity,
mechanical strength, and dopant incorporation, wherein the dopants
are metals remaining in the metal catalyst beads from the chloride
solution (e.g., Ni from NiCl.sub.2, Co from CoCl.sub.2, etc.).
[0012] These and other features and advantages of the present
invention will become apparent from the following description of
the invention, when viewed in accordance with the accompanying
drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a flow chart illustrating bead formation in
accordance with an embodiment of the present invention.
[0014] FIG. 2 includes X-ray diffraction patterns of MoO.sub.3
beads prepared at different gelation conditions.
[0015] FIG. 3 includes X-ray diffraction patterns of
Nb.sub.2O.sub.5 beads prepared at different gelation
conditions.
[0016] FIG. 4 includes X-ray diffraction patterns of WO.sub.3 beads
prepared at different gelation conditions.
[0017] FIG. 5 is a schematic representation of bulk metal oxide
beads undergoing activation under a flow of carburizing gas to form
bulk metal carbide beads.
[0018] FIG. 6 includes X-ray diffraction patterns of Mo.sub.2C
beads obtained by temperature programmed carburization of MoO.sub.3
beads contaminated by unreacted Ca.
[0019] FIG. 7 includes X-ray diffraction patterns of Mo.sub.2C
beads obtained by temperature programmed carburization of MoO.sub.3
beads free of unreacted CaCl.sub.2.
DETAILED DESCRIPTION OF THE CURRENT EMBODIMENTS
[0020] The invention as contemplated and disclosed herein includes
a method for synthesizing beads (or pellets) of bulk transition
metal carbides, nitrides and phosphides. As set forth more fully
below, the method involves the activation of oxide beads via
temperature programmed carburization, nitridation or phosphidation,
resulting in catalyst beads that are catalytically active and
mechanically robust, and that expand potential industrial
application of transition metal catalyst materials as unsupported
bulk catalysts.
[0021] Referring now to FIG. 1, a flow chart illustrating
transition metal catalyst bead formation is presented. In general
terms, a method for preparing transition metal catalyst beads in
accordance with one embodiment can include the following steps or
stages: a) forming an oxide slurry, b) preparing a an aqueous salt
solution, c) dropping or pipetting the oxide slurry into the
aqueous salt solution, d) collecting, washing and/or drying oxide
beads from the aqueous salt solution, e) heat treating the oxide
beads to remove the binder, and f) activating the oxide beads
through temperature programmed carburization, nitridation or
phosphidation to transform the oxide beads into carbide, nitride,
or phosphide transition metal catalysts. As used herein, "bead" and
"beads" refers to beads, pellets, granules and other dimensionally
stable masses, including those that are spherical, non-spherical,
porous, non-porous, solid, and hollow.
[0022] Forming the oxide slurry is depicted as step 10 in FIG. 1.
The oxide slurry includes a binder solution that is used as the
base system for a metal oxide powder. The binder solution can
include any gelling polysaccharides, and includes sodium alginate
in the present embodiment. The metal oxide powder is water
insoluble, and is suspended in the sodium alginate. Example metal
oxide powders include MoO.sub.3, Nb.sub.2O.sub.5, and WO.sub.3.
These metal oxides are exemplary, as essentially any water soluble
transition metal oxide (and mixtures thereof) can be utilized,
including for example, TiO.sub.2 or ZrO.sub.2. Other transition
metals forming oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr,
Nb, Mo, Tc, La, Hf, Ta, W, Re, Os, and combinations thereof. In
addition, the concentration and molecular weight of alginate are
variable, and varying the concentration and molecular weight of the
alginate influences the bead size, bead porosity, and bead
mechanical strength of the finished catalyst beads. Chitin and/or
chitosan can also be included in a gel forming base, and
subsequently dropped into an aqueous solution at a specific pH
(instead of an aqueous salt solution) to drive the gelling process
described below.
[0023] Preparing the aqueous salt solution is depicted as step 12
in FIG. 1. The aqueous salt solution can include any mono-valent
and di-valent metal salt, and includes a dilute solution of
CaCl.sub.2 in the present embodiment. In other embodiments the
aqueous sale solution includes other water soluble chlorides with
appropriate valence states. For example, the aqueous salt solution
can include CoCl.sub.2, NiCl.sub.2 or CuCl.sub.2. Contrary to Ca,
many other elements can decrease the activation temperature (i.e.,
facilitating reduction and incorporation of carbon, nitrogen or
phosphorous), enabling lower temperature synthesis with higher
specific surface areas. In addition, some metals are known catalyst
dopants or promoters, enhancing catalytic performance of carbides,
nitrides and phosphides. Accordingly, increasing the amount of
unreacted CoCl.sub.2, NiCl.sub.2 or CuCl.sub.2 can fine tune the
catalytic performance of the resulting carbide, nitride, or
phosphide beads. Employing water insoluble metal oxides containing
heteroatoms such as phosphorous can also control the activation
process as well as the properties of the synthesized carbide,
nitride, and phosphide beads.
[0024] Dropping the oxide slurry into the chloride solution is
depicted as step 14. In the present embodiment, the oxide slurry is
pipetted into the dilute solution of a metal chloride such as
CaCl.sub.2. Each droplet, when submerged in the metal chloride
solution, forms a gel, essentially setting the droplet into a bead.
In particular, the sodium ions in the binder solution exchange with
the calcium ions in the chloride solution, and the alginate chains
become cross-linked. The resulting oxide beads are then removed
from the chloride solution at step 16 to eliminate excess moisture
from the bead. For example, the beads are generally sieved or
filtered out of the chloride solution, rinsed repeatedly in
deionized water to remove residual salts that may be present on the
bead surfaces, and dried at room temperature. After the beads are
dry, they can be heat-treated or sintered in air to remove the
binder and further enhance the mechanical strength of the oxide
beads (depicted as step 18 in FIG. 1).
[0025] As shown in FIGS. 2-4, X-ray diffraction patterns of
MoO.sub.3 beads, Nb.sub.2O.sub.5 beads, and WO.sub.3 beads prepared
at different gelation conditions are depicted. In particular, X-ray
diffraction patterns are depicted in FIG. 2 for MoO.sub.3 beads
prepared using a CaC1 chloride solution, MoO.sub.3 beads prepared
using a NiCl.sub.2 chloride solution, and MoO.sub.3 beads prepared
using a CuCl.sub.2 chloride solution. As shown in FIG. 3, X-ray
diffraction patterns are depicted for Nb.sub.2O.sub.5 beads
prepared at three different gelation conditions including a
CaCl.sub.2 chloride solution, a NiCl.sub.2 chloride solution and a
CuCl.sub.2 chloride solution. Lastly, FIG. 4 includes X-ray
diffraction patterns for WO.sub.3 beads prepared at three different
gelation conditions, including a CaCl.sub.2 chloride solution, a
NiCl.sub.2 chloride solution and a CuCl.sub.2 chloride solution.
Variables that can control oxide bead size, porosity, and
mechanical strength include the concentration and molecular weight
of the alginate, the amount of oxide powder, the concentration of
the metal chloride solutions, the duration of the gelling time
(i.e., the time the beads is submerged in the chloride solution),
and the sintering conditions.
[0026] Activating the prepared oxide beads is depicted as step 20
in FIG. 1. Transformation of the prepared oxide beads into
catalytically active bulk carbide, nitride, and phosphide beads is
effected by temperature programmed activation. The temperature
programmed activation includes increasing the temperature slowly
and in a controlled manner in a flow of a reducing gas mixture
within a reactor. For carburization, the reducing gas mixture
includes a carburizing gas mixture, for example CH.sub.4, CO,
C.sub.2H.sub.6, other light hydrocarbons and combinations thereof,
in H.sub.2 gas. For nitriding, the reducing gas mixture includes a
nitriding gas mixture, for example NH.sub.3 in H.sub.2 gas. For
phosphiding, the reducing gas mixture includes a phosphiding gas
mixture, for example PH.sub.3 in H.sub.2 gas. As shown in FIG. 5,
for example, the reaction temperature gradually increases and in a
controlled manner. In particular, the reactor temperature is
linearly raised at a constant rate from room temperature until
reaching the desired temperature, and then remaining at this
temperature for an isothermal period. For example, the ramping rate
can be about 1.degree. C./min in some embodiments, while in other
embodiments the ramping rate can be about 5.degree. C./min. At the
conclusion of the isothermal temperature, the reactor temperature
decreases to room temperature. The resulting bulk metal carbide
beads can be subject to post-activation treatments as also depicted
in FIG. 5. It is to note that the activated carbide, nitride, and
phosphide catalysts are highly active and can be pyrophoric.
Therefore after the activation step, the catalyst beads need to be
passivated for example by treating them at room temperature in an
inert gas flow with low O.sub.2 content before exposure to ambient
air.
[0027] Though the reaction temperature is described above as
increasing at a constant rate to the desired temperature, the
reaction temperature can increase according to other temperature
profiles as desired. For example, the activation (e.g.,
carburization) of the prepared oxide bead can include several
intermediate soak temperatures and/or ramping rates. Further by
example, the activation of the prepared oxide bead can include a
ramping rate of 5.degree. C./min from room temperature to
300.degree. C. and then 1.degree. C./min from 300.degree. C. to
700.degree. C. Isothermal activation is also possible, in which the
activation temperature remains substantially constant.
[0028] One aspect of the present method includes the minimization
of Ca residues during the oxide shaping step. In particular, alkali
metals can prevent or delay the activation of transition metals,
resulting in an incomplete carburization or nitridation, for
example. For instance, carburization of Ca-contaminated MoO.sub.3
beads can lead to a mixture of Mo carbides, Mo metal and Mo oxides,
which are not effective catalysts. As shown in FIG. 6, X-ray
diffraction of the transition metal beads confirmed the presence of
Mo metal and Mo oxides. In addition, Mo.sub.2C was confirmed as
present, related to the presence of Ca ions that were not
completely removed from metal oxide beads prior to temperature
programmed carburization. Although leaving some Ca ions is
inevitable since cross-linking alginate requires them, by
thoroughly removing unreacted CaCl.sub.2, clean carbides, nitrides
and phosphide phases can be obtained. In FIG. 7 for example,
MoO.sub.3 beads were prepared using a NiCl.sub.2 solution (graph-a)
or a CaCl.sub.2 solution (graph-b) and activated by temperature
programmed carburization with a minimal contamination of the
MoO.sub.3 beads with Ca residues (graph-b). The X-ray diffraction
of the transition metal carbide illustrates that only the Mo.sub.2C
phases are visible.
[0029] The above embodiment therefore provides a method to prepare
catalyst beads of bulk transition metal carbides, nitrides, and
phosphides. The bulk transition metal catalysts can include, for
example, molybdenum carbide, molybdenum nitride, molybdenum
phosphide, tungsten carbide, tungsten nitride, or tungsten
phosphide. Other bulk metal carbides, nitrides, or phosphides can
be synthesized as desired. The above method can be tuned for the
control of porosity, mechanical strengths, and dopant content of
beads. In addition, dopant elements can be incorporated during
oxide bead shaping; Ni can, for example be incorporated by using
NiCl.sub.2 to prepare metal salt solution. Activation of
as-prepared oxide beads via temperature programmed carburization,
nitridation, and phosphidation can result in bulk metal carbide,
nitride, and phosphide catalysts beads, respectively. As bulk
catalysts, the beads can be used in packed-bed reactor
applications, for instance for biomass conversion, petroleum
refining, and other applications.
EXAMPLE 1
[0030] Mo.sub.2C transition metal beads were synthesized according
to the following example, which is intended to be non-limiting.
[0031] An oxide slurry was obtained by suspending 50 wt % of
molybdenum oxide in an alginate solution made from a 1 to 1 ratio
of 5 wt % low molecular weight alginate and 1 wt % high molecular
weight alginate. The oxide slurry was pipetted into a 2 wt %
calcium chloride solution at room temperature. The mixture was
allowed to stand for 2 to 30 minutes to allow the oxide slurry to
solidify, during which time sodium ions in the oxide slurry
exchange with calcium ions in the chloride solution. Molybdenum
oxide beads were removed from the calcium chloride solution, rinsed
in deionized water, and dried in air at room temperature for 24
hours. The oxide beads were then heat treated at 600.degree. C. for
2 hours in air to remove any residual binder solution and to
enhance the mechanical strength of the oxide beads. The oxide beads
were then transferred to a reactor and activated according to a
temperature programmed carburization method. In particular, the
temperature of reactor was increased from room temperature in a
linear rate of 1.degree. C. per minute to 700.degree. C., and
remaining at this temperature for 1 hour, all while under a flow of
CH.sub.4/H.sub.2 gas at approximately 100 mL/minute per gram of
oxide with a mixture ratio of 15% CH.sub.4 in H.sub.2. The beads
were then cooled to room temperature in an inert gas flow and were
passivated in a low concentration of O.sub.2 in an inert gas flow
for at least 10 hours before exposing to air. The resulting
Mo.sub.2C transition metal beads demonstrated hexagonal close
packed crystallography, having desirable surface area and site
density.
EXAMPLE 2
[0032] Mo.sub.2C transition metal beads were synthesized according
to the following example, which is intended to be non-limiting.
[0033] An oxide slurry was obtained by suspending 50 wt % of
molybdenum oxide in an alginate solution made from a 1 to 1 ratio
of 5 wt % low molecular weight alginate and 1 wt % high molecular
weight alginate. The oxide slurry was pipetted into a 2 wt % nickel
chloride solution at room temperature. The mixture was allowed to
stand for 2 to 30 minutes to allow the oxide slurry to solidify,
during which time sodium ions in the oxide slurry exchange with
nickel ions in the chloride solution. Molybdenum oxide beads were
removed from the nickel chloride solution, rinsed in deionized
water, and dried in air at room temperature for 24 hours. The oxide
beads were then heat treated at 600.degree. C. for 2 hours in air
to remove any residual binder solution and to enhance the
mechanical strength of the oxide beads. The oxide beads were then
transferred to a reactor and activated according to a temperature
programmed carburization method. In particular, the temperature of
reactor was increased from room temperature in a linear rate of
1.degree. C. per minute to 700.degree. C., and remaining at this
temperature for 1 hour, all while under a flow of CH.sub.4/H.sub.2
gas at approximately 100 mL/minute per gram of oxide with a mixture
ratio of 15% CH.sub.4 in H.sub.2. The beads were then cooled to
room temperature in an inert gas flow and were passivated in a low
concentration of O.sub.2 in an inert gas flow for at least 10 hours
before exposing to air. The resulting Mo.sub.2C transition metal
beads demonstrated hexagonal close packed crystallography, having
desirable surface area and site density.
EXAMPLE 3
[0034] WC transition metal beads were synthesized according to the
following example, which is intended to be non-limiting.
[0035] An oxide slurry was obtained by suspending 50 wt % of
tungsten oxide in an alginate solution made from 1 wt % high
molecular weight alginate. The oxide slurry was pipetted into a 2
wt % copper chloride solution at room temperature. The mixture was
allowed to stand for 2 to 30 minutes to allow the oxide slurry to
solidify, during which time sodium ions in the oxide slurry
exchange with copper ions in the chloride solution. Tungsten oxide
beads were removed from the copper chloride solution, rinsed in
deionized water, and dried in air at room temperature for 24 hours.
The oxide beads where then sintered at 1000.degree. C. for 2 hours
in air to remove any residual binder solution and to enhance the
mechanical strength of the oxide beads. The oxide beads were then
transferred to a reactor and activated according to temperature
programmed carburization. In particular, the temperature of reactor
was increased from room temperature in a linear rate of 20.degree.
C. per minute to 827.degree. C., and remaining at this temperature
for 6 hours all while under a flow of CH.sub.4/H.sub.2 gas at
approximately 100 mL/minute per gram of oxide with a mixture ratio
of 80% CH.sub.4 in H.sub.2. The temperature was then lowered to
700.degree. C. in an inert gas for an H.sub.2 treatment for 2 hours
to remove polymeric carbon deposited on the surface. The carbide
beads were subsequently cooled to room temperature in an inert gas
flow and were passivated in a low concentration of O.sub.2 in an
inert gas flow for at least 10 hours before exposing to air. The
resulting WC transition metal beads demonstrated simple hexagonal
crystallography, having desirable surface area and site
density.
[0036] The above description is that of current embodiments of the
invention. Various alterations and changes can be made without
departing from the spirit and broader aspects of the invention as
defined in the appended claims, which are to be interpreted in
accordance with the principles of patent law including the doctrine
of equivalents. Any reference to elements in the singular, for
example, using the articles "a," "an," "the," or "said," is not to
be construed as limiting the element to the singular.
* * * * *