U.S. patent application number 11/398003 was filed with the patent office on 2007-10-11 for fuel reformer catalyst.
Invention is credited to Laiyuan Chen, Jeffrey G. Weissman.
Application Number | 20070238610 11/398003 |
Document ID | / |
Family ID | 38576063 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070238610 |
Kind Code |
A1 |
Chen; Laiyuan ; et
al. |
October 11, 2007 |
Fuel reformer catalyst
Abstract
A fuel reformer catalyst includes a substrate, and disposed
thereon a carrier and combination of at least two metals selected
from the group consisting of Rh, Ni, Ir, Pd, Pt, Au, and
combinations thereof. Rh is present in the catalyst in an amount
not exceeding about 0.5 wt. %, based on the total combined weight
of the metals and carrier.
Inventors: |
Chen; Laiyuan; (Broken
Arrow, OK) ; Weissman; Jeffrey G.; (Broken Arrow,
OK) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC.
M/C 480-410-202
PO BOX 5052
TROY
MI
48007
US
|
Family ID: |
38576063 |
Appl. No.: |
11/398003 |
Filed: |
April 5, 2006 |
Current U.S.
Class: |
502/330 ;
502/326 |
Current CPC
Class: |
C01B 2203/1082 20130101;
C01B 2203/142 20130101; B01J 23/894 20130101; C01B 2203/0261
20130101; B01J 37/0215 20130101; B01J 23/63 20130101; C01B 3/382
20130101; B01J 35/04 20130101; Y02P 20/141 20151101; C01B 2203/1047
20130101; C01B 2203/0233 20130101; C01B 3/40 20130101; B01J 23/892
20130101; Y02P 20/142 20151101; C01B 2203/1058 20130101; C01B
2203/107 20130101; B01J 35/0006 20130101; C01B 2203/0244 20130101;
Y02P 20/52 20151101; C01B 2203/1064 20130101; C01B 2203/0238
20130101; C01B 3/38 20130101 |
Class at
Publication: |
502/330 ;
502/326 |
International
Class: |
B01J 23/38 20060101
B01J023/38 |
Claims
1. A fuel reformer catalyst comprising a substrate, and disposed
thereon a carrier and a combination of at least two metals selected
from the group consisting of Rh, Ni, Ir, Pd, Pt, Au, and
combinations thereof, wherein the Rh is present in said catalyst in
an amount not exceeding about 0.5 wt. %, based on the total
combined weight of said metals and said carrier.
2. The fuel reformer catalyst of claim 1 comprising a substrate,
and disposed thereon a combination of at least two metals selected
from the group consisting of Ni, Ir, Pd, Pt, Au, and combinations
thereof.
3. The fuel reformer catalyst of claim 1 wherein said Ni is present
in an amount of about 0.1 wt. % to about 20 wt. %, based on the
total weight of said metals and said carrier.
4. The fuel reformer catalyst of claim 3 wherein said Ni is present
in an amount of about 1 wt. % to about 10 wt. %, based on the total
weight of said metals and said carrier.
5. The fuel reformer catalyst of claim 4 wherein said Ni is present
in an amount of about 5 wt. %, based on the total weight of said
metals and said carrier.
6. The fuel reformer catalyst of claim 1 wherein said Ir, Pd, Pt,
Au, and combinations thereof are each present in an amount of about
0.1 wt. % to about 10 wt. %, based on the total weight of said
metals and said carrier.
7. The fuel reformer catalyst of claim 6 wherein said Ir, Pd, Pt,
Au, and combinations thereof are each present in an amount of about
0.5 wt. % to about 5 wt. %, based on the total weight of said
metals and said carrier.
8. The fuel reformer catalyst of claim 7 wherein said Ir, Pd, Pt,
Au, and combinations thereof are each present in an amount of about
1 wt. % to about 2 wt. %, based on the total weight of said metals
and said carrier.
9. The fuel reformer catalyst of claim 1 wherein said substrate is
selected from the group consisting of spinel, cordierite,
zirconia-mullite, titanium aluminate, calcium aluminate, .gamma.-,
.theta.- .alpha.-, and .delta.-alumina, alumina stabilized by La,
Ba, Mg, or Ca, zirconium-toughened alumina (ZTA), and combinations
thereof.
10. The fuel reformer catalyst of claim 9 wherein said substrate is
selected from the group consisting of metal-stabilized
.gamma.-alumina, zirconia-mullite, zirconium-toughened alumina
(ZTA), and combinations thereof.
11. The fuel reformer catalyst of claim 1 wherein carrier and said
combination of said metals comprise a washcoat, said washcoat being
applied to said substrate.
12. The fuel reformer catalyst of claim 1 contained within a
reactor vessel, said vessel comprising an inlet for fuel and an
outlet for product reformate.
13. The fuel reformer catalyst of claim 12 comprising a first stage
and a second stage, said first stage being disposed proximate said
inlet of said vessel, and said second stage being disposed
proximate said outlet of said vessel.
14. The fuel reformer catalyst of claim 13 wherein said first stage
catalyst comprises a metal selected from the group consisting of
Ir, Pt, and combinations thereof.
15. The fuel reformer catalyst of claim 14 wherein said Ir, Pt, and
combinations thereof are each present in an amount of about 0.1 wt.
% to about 10 wt. %, based on the total weight of said first stage
metals and said carrier.
16. The fuel reformer catalyst of claim 15 wherein said Ir is
present in an amount of about 10 wt. %, based on the total weight
of said first stage metals and said carrier.
17. The fuel reformer catalyst of claim 15 wherein said Pt is
present in an amount of about 5 wt. %, based on the total weight of
said first stage metals and said carrier.
18. The fuel reformer catalyst of claim 13 wherein said second
stage catalyst comprises a metal selected from the group consisting
of Rh, Ni, Ir, Pd, Pt, and combinations thereof, wherein the Rh is
present in said second catalyst in an amount not exceeding about
0.5 wt. %, based on the total weight of said second stage metals
and said carrier.
19. The fuel reformer catalyst of claim 18 wherein said second
stage catalyst comprises about 0.5 wt. % Rh.
20. The fuel reformer catalyst of claim 18 wherein said second
stage catalyst comprises a metal selected from the group consisting
of Ni, Ir, Pd, Pt, Au, and combinations thereof.
21. The fuel reformer catalyst of claim 18 wherein said second
stage catalyst comprises a metal selected from the group consisting
of Ni, Ir, Pd, Pt, Au, and combinations thereof.
22. The fuel reformer catalyst of claim 21 wherein said Ir, Pd, Pt,
Au, and combinations thereof are each present in an amount of about
0.1 wt. % to about 10 wt. %, based on the total weight of said
second stage metals and said carrier.
23. The fuel reformer catalyst of claim 22 wherein said Ir, Pd, Pt,
Au, and combinations thereof are each present in an amount of about
1 wt. % to about 2 wt. %, based on the total weight of said second
stage metals and said carrier.
24. The fuel reformer catalyst of claim 21 wherein said Ni is
present in an amount of about 0.1 wt. % to about 20 wt. %, based on
the total weight of said second stage metals and said carrier.
25. The fuel reformer catalyst of claim 24 wherein said Ni is
present in an amount of about 5 wt. %, based on the total weight of
said second stage metals and said carrier.
Description
TECHNICAL FIELD
[0001] The present invention relates to fuel reforming, in
particular the production of hydrogen-rich gaseous products from
hydrocarbons and an oxidant, and most particularly to catalysts to
facilitate the formation of such products.
BACKGROUND OF THE INVENTION
[0002] Tighter emission standards and significant innovation in
catalyst formulations and engine controls has led to dramatic
improvements in the low emission performance and robustness of
gasoline and diesel engine systems. However, many technical
challenges remain to make the conventionally fueled internal
combustion engine a nearly zero emission system having the
efficiency necessary to make the vehicle commercially viable.
[0003] The automotive industry has made very significant progress
in reducing automotive emissions in both the mandated test
procedures and the "real world". This has resulted in some added
cost and complexity of engine management systems, yet those costs
are offset by other advantages of computer controls: increased
power density, fuel efficiency, drivability, reliability and
real-time diagnostics. However future initiatives to require zero
emission vehicles are likely to provide smaller environmental
benefits at a very large incremental cost. Even so, an "ultra low
emission" certified vehicle may emit high emissions in limited
extreme ambient and operating conditions or with failed or degraded
components, and especially during cold start.
[0004] One approach to addressing the issue of emissions is the
employment of fuel cells, particularly solid oxide fuel cells
(SOFC), in an automobile as either a primary or secondary source of
power. A fuel cell is an energy conversion device that generates
electricity and heat by electrochemically combining a gaseous fuel,
such as hydrogen, carbon monoxide, or a hydrocarbon, and an
oxidant, such as air or oxygen, across an ion-conducting
electrolyte. The fuel cell converts chemical energy into electrical
energy. SOFCs are constructed entirely of solid-state materials,
utilizing an ion conductive oxide ceramic as the electrolyte. An
electrochemical cell in a SOFC may comprise an anode and a cathode
with an electrolyte disposed there between. The oxidant passes over
the oxygen electrode (cathode) while the fuel passes over the fuel
electrode (anode), generating electricity, water, and heat. The use
of the SOFC, and fuel cells in general, reduce emissions through
their much greater efficiency, and so require less fuel for the
same amount of power produced, as compared to conventional
hydrocarbon fueled engines. Additionally, a fuel cell may be
employed to supplement a conventional engine; in this way the
engine may be optimized for primary traction power, while the fuel
cell may provide other power needs for the vehicle, i.e.
air-conditioner, communication and entertainment devices. The fuel
reformer--fuel cell system may be operated while the engine is off,
permitting electrically powered devices to operate, thereby further
reducing emissions by providing power using a more fuel efficient
fuel cell to meet the vehicle operator's needs.
[0005] To facilitate the production of electricity by the SOFC, a
direct supply of simple fuel, e.g., hydrogen, carbon monoxide,
and/or methane is preferred. However, concentrated supplies of
these fuels are generally expensive and difficult to supply.
Therefore the fuel utilized may be obtained by processing a more
complex fuel source. The actual fuel utilized in the system is
chosen based upon the application, expense, availability, and
environmental issues relating to the fuel. Possible fuels include
hydrocarbon fuels, including, but not limited to, liquid fuels,
such as gasoline, diesel fuel, ethanol, methanol, kerosene, and
others; gaseous fuels, such as natural gas, propane, butane, and
others; "alternative" fuels, such as biofuels, dimethyl ether, and
others; synthetic fuels, such as synthetic fuels produced from
methane, methanol, coal gasification or natural gas conversion to
liquids, and combinations comprising at least one of the foregoing
methods, and the like, as well as combinations comprising at least
one of the foregoing fuels. The preferred fuel is based upon the
types of equipment employed, with lighter fuels, i.e., those that
may be more readily vaporized and/or conventional fuels, which are
readily available to consumers being generally preferred.
[0006] Processing or reforming of hydrocarbon fuels such as
gasoline may provide an immediate fuel source for rapid start up of
the fuel cell and also protect the fuel cell by breaking down long
chain hydrocarbons and removing impurities. Fuel reforming may
include mixing fuel with air, water and/or steam in a reforming
zone before entering the reformer system, and converting a
hydrocarbon such as gasoline or an oxygenated fuel such as methanol
into hydrogen (H.sub.2) and carbon monoxide (CO), along with carbon
dioxide (CO.sub.2) methane (CH.sub.4), nitrogen (N.sub.2), and
water (H.sub.2O). Approaches to reforming include steam reforming,
partial oxidation, dry reforming, and combinations thereof. Both
steam reforming and dry reforming are endothermic processes, while
partial oxidation is an exothermic process.
[0007] Accordingly, a SOFC may be used in conjunction with a fuel
reformer to convert a hydrocarbon-based fuel to hydrogen and carbon
monoxide (the reformate) usable by a fuel cell. Preferably, the
reformer has a rapid start, a dynamic response time, and excellent
fuel conversion efficiency. It is also preferred for the reformer
to have a minimal size and reduced weight, as compared to other
power sources. However, reformers operate at temperatures that are
typically higher than about 600.degree. C., and may even exceed
1000.degree. C. At lower temperatures, for example during start-up,
deposition of carbonaceous matter, or soot, upon the catalyst may
adversely affect the reformer's efficiency, reduce reformer life,
and/or damage fuel cell components. Accordingly, it is beneficial
to reduce the time required by a reformer and/or fuel cell system
to reach an operational temperature.
[0008] Of the various types of reformers available, the type of
reformer technologies preferred depend in part on the type of fuel
to be used. Steam reformers (SR) are generally employed for
converting methanol to hydrogen. Partial oxidation (POX) reformers
are generally employed for converting gasoline to hydrogen and
carbon monoxide.
[0009] Steam reforming systems involve the use of a fuel and steam
(H.sub.2O) that is reacted in heated tubes filled with catalysts to
convert the hydrocarbons into principally hydrogen and carbon
monoxide. The steam reforming reactions are endothermic; thus the
steam reformer reactors are designed to transfer heat into the
catalytic process. An example of the steam reforming reaction is as
follows: CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2
[0010] Partial oxidation reformers are based on substoichiometric
combustion to achieve the temperatures necessary to reform the
hydrocarbon fuel. Decomposition of the fuel to primarily hydrogen
and carbon monoxide occurs through thermal reactions at high
temperatures of about 600.degree. C. to about 1200.degree. C., and
preferably, about 700.degree. C. to about 1050.degree. C. Catalysts
have been used with partial oxidation systems to promote conversion
of various low sulfur fuels into synthesis gas. The use of a
catalyst may result in acceleration of the reforming reactions and
also enable the use of lower reaction temperatures than would
otherwise be required in the absence of a catalyst. An example of
the partial oxidation reforming reaction is as follows:
CH.sub.4+1/2O.sub.2.fwdarw.CO+2H.sub.2
[0011] U.S. Pat. No. 2,892,693, the disclosure of which is
incorporated herein by reference, discloses a method for producing
carbon monoxide and hydrogen from gaseous hydrocarbons in which
steam is reacted with the hydrocarbon at an elevated pressure over
a catalyst to effect partial conversion of the hydrocarbon,
followed by reaction of the unconverted hydrocarbon contained in
the effluent from the steam-hydrocarbon reforming reaction with
oxygen in a zone of partial combustion.
[0012] Dry reforming involves the creation of hydrogen and carbon
monoxide in the absence of water using, for example, carbon dioxide
as the oxidant. Dry reforming reactions, like steam reforming
reactions, are endothermic processes. An example of the dry
reforming reaction is depicted in the following reaction:
CH.sub.4+CO.sub.2.fwdarw.2CO+2H.sub.2
[0013] Practical reformer systems may include a combination of
these idealized processes. Thus, a combination of air, water and/or
recycled engine exhaust gas may be used as the oxidant in the fuel
reforming process.
SUMMARY OF THE INVENTION
[0014] The present invention is directed to a fuel reformer
catalyst comprising a substrate, and disposed thereon a carrier and
a combination of at least two metals selected from the group
consisting of Rh, Ni, Ir, Pd, Pt, Au and combinations thereof. Rh
is present in the catalyst in an amount not exceeding about 0.5 wt.
%, based on the total combined weight of the metals and the
carrier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic representation of a two-stage reformer
catalyst in accordance with the present invention, wherein the
first stage is proximate the fuel inlet and the second stage is
proximate the reformate outlet of a reactor vessel (not shown).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] As disclosed in U.S. Pat. No. 6,832,473, the disclosure of
which is incorporated herein by reference, a fuel reformer
comprises a substrate and a catalyst, which can be applied to the
substrate in various ways, for example, by washcoating employing
the use of a carrier, imbibition, impregnation, physisorption,
chemisorption, or precipitation. Washcoating is a convenient
preferred means of applying the catalyst to the substrate.
[0017] The reformer substrate is preferably capable of operating at
temperatures up to about 1200.degree. C. and of withstanding
reducing and oxidizing environments containing, for example,
hydrocarbons, hydrogen, carbon monoxide, water, oxygen, sulfur and
sulfur-containing compounds, combustion radicals such as hydrogen
and hydroxyl ions, and carbon particulate matter. In addition, the
substrate must have sufficient surface area and structural
integrity to support the desired catalytically active metals and
carrier.
[0018] Materials that can be used for the reformer substrate
include alumina, zirconia, lanthanum oxide, cordierite, mullite,
silicon carbide, and metals such as stainless steel, aluminum, or
stainless steel or aluminum alloyed with chromium, yttrium and the
like, as well as oxides, alloys, cermets, and mixtures comprising
at least one of the foregoing materials. Preferred ceramic
substrates include spinel, cordierite, zirconia-mullite, titanium
aluminate, calcium aluminate, .gamma.-, .theta.-, .alpha.-, and
.delta.-alumina, alumina stabilized by La, Ba, Mg, or Ca,
zirconium-toughened alumina (ZTA), ceramics containing at least 25
wt. % ZrO.sub.2, and combinations thereof. Particularly preferred
substrates include metal-stabilized .gamma.-alumina,
zirconium-toughened alumina (ZTA), ceramics containing at least 25
wt. % ZrO.sub.2, and combinations thereof.
[0019] Although the reformer substrate can have any size or
geometry, the size and geometry are preferably chosen to optimize
the surface area in the given catalytic converter design
parameters. The reformer substrate can have an open cell foam
structure, or an extruded honeycomb cell geometry, with the cells
being any multi-sided or rounded shape, with substantially square,
hexagonal, octagonal or similar geometries preferred for reasons of
increased surface area and structural integrity. The substrate is
formed into a cell structure with a plurality of cells arranged in
a honeycomb pattern using a foam process, and the like.
[0020] Additives to the substrate may include, for example, oxygen
storage compounds such as CeO.sub.2 or CeO.sub.2--ZrO.sub.2 solid
solution.
[0021] Reformer catalyst materials include metals, such as nickel,
platinum, palladium, rhodium, iridium, gold, osmium, ruthenium, and
the like, and oxides, mixtures, and alloys comprising the foregoing
metals. Preferably, the metal is selected from among the platinum
group metals (PGM): platinum (Pt), iridium (Ir), palladium (Pd),
and rhodium (Rh), and, in addition, gold (Au). All of the PGMs are
expensive; however, as shown below, they vary greatly in cost, Ir
being the least expensive, Rh by far the most expensive:
TABLE-US-00001 Metal Cost ($/g as of Feb. 14, 2006) Pt 1015 Ir 205
Pd 278 Rh 3050
[0022] Despite its high cost, Rh is included, typically at a
concentration of about 1-2 wt. %, based on the total combined
weight of Rh and carrier, in currently preferred reformer
catalysts. It would be highly desirable to reduce substantially the
amount of Rh, even to zero, in the catalyst formulation.
[0023] The reformer catalyst of the present invention preferably
includes at least one PGM, Ir, Pd, and Pt, or Au, and combinations
thereof, each metal being present in an amount of preferably about
0.1 wt. % to about 10 wt. %, more preferably about 0.5 wt. % to
about 5 wt. %, most preferably about 1 wt. % to about 2 wt. %,
based on the total weight of the total combined weight of metals
and carrier.
[0024] In addition to the PGM components, the catalyst may also
include Ni in an amount preferably of about 0.1 wt. % to about 20
wt. %, more preferably about 1 wt. % to about 10 wt. %, most
preferably about 5 wt. %, based on the total weight of metals and
carrier.
[0025] Metal loadings, expressed a grams of total metal per cubic
foot of substrate (g/ft.sup.3), can range from about 1 to 500
g/ft.sup.3, with a preferred range of about 10 to 250 g/ft.sup.3,
and a more preferred range of about 50 to 120 g/ft.sup.3. Too low a
metal loading does not lead to sufficient catalytic activity, while
no benefit results from additional metal above a certain effective
amount.
[0026] Suitable carriers include transitional metal oxides, such as
alumina (Al.sub.2O.sub.3), including gamma, alpha, delta, or theta
phases, silica (SiO.sub.2) in either quartz, cristobalite, or
tridymite forms, zirconia (ZrO.sub.2) In either the monoclinic or
tetragonal form, oxides of lanthanum (La), yttrium (Y), cerium
(Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), ytterbium
(Yb), or scandium (Sc). Combinations of these are possible,
including incorporation of oxides of magnesium (Mg), calcium (Ca),
strontium (Sr) or barium (Ba), to form compounds with spinel,
magnetoplumbite, hexaluminate, perovskite, or fluorite structures,
of general formula A.sub.wB.sub.xC.sub.yD.sub.zO.sub.n, in which A,
B, C, D is any of the oxides mentioned above, O is oxygen, and w,
x, y, z, and n are molar quantities required for stoichiometric
balance. Examples of suitable compounds include .theta.- or
.delta.-alumina, monoclinic zirconia, magnesium spinel
(MgAl.sub.2O.sub.4), lanthanum hexaluminate LaAl.sub.11O.sub.18,
alumina mixed with ceria-zirconia-lanthana mixed oxide, and other
combinations.
[0027] The carrier can have a surface area 1 to over 300 square
meters per gram (m.sup.2/g), preferably about 10 to 200 m.sup.2/g,
more preferably about 35 to 70 m.sup.2/g. A lower surface area may
not provide enough surface to carry the active metal, while a
higher surface area may result in a carrier more prone to sintering
and loss of surface area. While particle size of the carrier is not
important, a preferred range is about 1 to 20.mu., more preferably,
about 4 to 9.mu..
[0028] In one embodiment of the present invention, a reformer
catalyst comprises a substrate, and disposed thereon a combination
of at least two metals selected from the group consisting of Rh,
Ni, Ir, Pd, and Pt, wherein the Rh is present in the catalyst in an
amount not exceeding about 0.5 wt. %, based on the total weight of
metals and carrier. A low concentration of Rh of about 0.5 wt %,
which results in a substantial reduction in catalyst cost, is
sufficient to maintain good catalyst performance and
durability.
[0029] In another embodiment of the present invention, a reformer
catalyst comprises a substrate, and disposed thereon a carrier and
a combination of at least two metals selected from the group
consisting of Ni, Ir, Pd, Pt, and Au, no Rh being present in the
metal combination.
[0030] In still another embodiment of the present invention, a
reformer catalyst comprises a first stage and a second stage,
wherein each of the stages comprises a substrate, and disposed
thereon a metal selected from the group consisting of Rh, Ni, Ir,
Pd, Pt, and Au, wherein the Rh is present in each stage in a total
amount not exceeding about 0.5 wt. %, based on the total combined
weight of metals and carrier. The catalyst is enclosed in a reactor
vessel provided with an inlet for fuel and an outlet for product
reformate, the first and second stages of the catalyst being
disposed proximate the inlet and outlet, respectively An
illustrative example of a two-stage reformer catalyst that includes
Pt or Ir in the first stage and Ir--Ni or Pd--Ni in the second
stage is schematically depicted in FIG. 1.
[0031] The first stage of the reformer catalyst preferably
comprises a metal selected from the group consisting of Ir, Pt, and
combinations thereof, Ir and Pt each being present in an amount of
about 0.1 wt. % to about 10 wt. %, based on the total combined
weight of the first stage metals and carrier. More preferably, Ir
is present in an amount of about 10 wt. %, and Pt is present in an
amount of about 5 wt. %, based on the total combined weight of the
first stage metals and carrier.
[0032] The second stage catalyst preferably comprises a metal
selected from the group consisting of Rh, Ni, Ir, Pd, Pt, Au, and
combinations thereof, wherein the Rh is present in said second
catalyst in an amount not exceeding about 0.5 wt. %, based on the
total combined weight of the second stage metals and carrier. More
preferably, the second stage catalyst comprises about 0.5 wt. %
Rh.
[0033] In a further embodiment, the second stage catalyst comprises
a metal selected from the group consisting of Ni, Ir, Pd, Pt, Au,
and combinations thereof, the Ir, Pd, Pt, Au, and combinations
thereof being present in an amount that is preferably about 0.1 wt.
% to about 10 wt. %, based on the total combined weight of the
second stage metals and carrier. More preferably, the Ir, Pd, Pt,
Au, and combinations thereof are present in an amount of about 1
wt. % to about 2 wt. %, based on the total combined weight of the
second stage metals and carrier. Ni is present in an amount that is
preferably about 0.1 wt. % to about 20 wt. %, more preferably about
5 wt. %, based on the total combined weight of the second stage
metals and carrier.
[0034] The two-stage reformer catalyst of the present invention,
which produces advantages in catalyst durability and hydrogen
selectivity, is widely applicable to fuel reformer processes,
including catalytic partial oxidation (POX), steam reforming (SR),
and autothermal reforming (ATR) processes.
Catalyst Preparation
[0035] A comparison reformer catalyst and several illustrative
examples of reformer catalysts in accordance with the present
invention were prepared as described below:
[0036] 1) 1 wt. % Rh (Comparison) [0037] 4.77 g rhodium nitrate
(10.58 wt. % Rh) was mixed with 50-60 g deionized water, and the
resulting solution was added to 50 g dry .theta.-alumina (5 wt % Ba
modified) powder. This mixture was then ball milled to give a
slurry having a pH of about 3.5-4.0 and containing 30-50 wt. %
solids, the average particle size being 5 .quadrature.m. This
slurry was used to washcoat a 20 PPI ZTA foam substrate.
[0038] 2) 2 wt. % Ir-2 wt. % Ni (Invention) [0039] 1.96 g iridium
(IV) chloride hydrate (52.93 wt. % Ir, from Strem Chemicals) and
4.56 g Ni(Ac).sub.2.4H.sub.2O (from Alfa Aesar) were dissolved in
55 g deionized water. The resulting solution was mixed with 50 g
La.sub.2O.sub.3 powder, with a small amount of alumina as a binder.
The mixture was milled to provide a slurry, which was applied to
the 20 PPI ZTA substrate by washcoating.
[0040] 3) 1 wt. % Pd-5 wt. % Ni (Invention) [0041] 3.38 g palladium
nitrate (14.77 wt. % Pd) and 10.5 g nickel acetate tetrahydrate
were dissolved in 60 g deionized water. The resulting solution was
mixed with 50 g alumina powder, and the mixture was milled to give
a slurry having a pH of about 3.5-4.0 and containing 35-40 wt. %
solids, the average particle size being 5 .mu.m. This slurry was
used to washcoat the 20 PPI ZTA substrate.
[0042] 4) 5 wt. % Pt (Invention) [0043] 9.75 g platinum nitrate
(25.64 wt. % Pt) was dissolved in 60 g deionized water, and the
resulting solution was mixed with 50 g alumina powder.
[0044] This mixture was milled to produce a slurry that was used to
coat a 45 PPI ZTA foam substrate (length 1/8'', diameter 1'').
[0045] 5) 0.5 wt. % Rh-1 wt. % Pd-5 wt. % Ni (Invention) [0046] The
method of preparation was similar to that of catalyst 3, except for
the metal solution used to make the slurry. 2.36 g rhodium nitrate
(10.58 wt. % Rh), 3.38 g palladium nitrate (14.77 wt. % Pd) and
10.5 g nickel acetate tetrahydrate were dissolved in 60 g deionized
water. The resulting solution was mixed with 50 g La.sub.2O.sub.3
modified .gamma.-alumina to make a slurry for washcoating. The
slurry, whose properties were similar to those in catalyst 3, was
applied to a 20 PPI ZTA foam substrate and a 400 cpsi
1''(D).times.1'' (L) zirconia-mullite monolith substrate,
respectively.
[0047] 6) 0.5 wt. % Rh-1 wt. % Pt-5 wt. % Ni (Invention) [0048] The
method of preparation was similar to that of catalyst 6, except for
the metal solution used to make the slurry. In this formulation,
1.98 g platinum nitrate (25.64 wt. % Pt), 2.32 g rhodium nitrate
(10.58 wt % Rh) and 10.5 g nickel acetate tetrahydrate were
dissolved in 60 g deionized water. The resulting solution was mixed
with 50 g La.sub.2O.sub.3 modified .gamma.-alumina to make a slurry
for washcoating. A 400 cpsi 1''(D).times.1'' (L) zirconia-mullite
monolith substrate was used. Catalyst Testing
[0049] The catalyst test reactor is a stainless steel vessel with
an inner diameter of about 1.25''. The catalyst was put in the
middle of the vessel, and a blank substrate without washcoat was
placed on both the top and the bottom of the catalyst to serve as a
mixing brick and heat retainer. Thermocouples were placed at the
top, center and bottom of the catalyst to measure temperatures.
Catalysts and blank substrates were retained inside the vessel via
alumina wrap.
[0050] Air flow was controlled by a mass flow controller, and 2007
Certification diesel fuel with added sulfur to 50 ppm was metered
with an ISCO syringe pump and heated by a vaporizer before
introduction into the reactor. The O/C ratio was 1.15, and the gas
space velocity was about 67000/hr. The product gas was analyzed by
an on-line gas chromatograph (micro-GC). Reaction temperatures were
about 1100-1200.degree. C.
[0051] Some of the catalysts were aged prior to testing, the aging
process being carried out at 1200.degree. C. in static air for 10
hours.
[0052] Desired reaction products for feed to a downstream SOFC
include H.sub.2 and CO, while undesired reaction products include
unconverted or partially converted hydrocarbons, such as methane
(CH.sub.4), ethane (C.sub.2H.sub.6), or ethylene (C.sub.2H.sub.4).
A downstream SOFC device will operate best with minimal hydrocarbon
content in the produced reformate. For example, CH.sub.4
concentration should be less than 1%, while total non-methane
hydrocarbon concentrations should be less than 0.2%. Assuming that
there is no accumulation of material in the reactor, higher
concentrations of H.sub.2 in the product reformate indicate that
lower concentrations of hydrocarbons are present in the reformate,
i.e., all hydrogen included in the reactants entering the reactor
leaves the reactor converted to H.sub.2 or H.sub.2O, or partially
converted to hydrocarbons.
[0053] A small change in H.sub.2 concentration could indicate a
significant increase in hydrocarbon concentration, from the
perspective of the SOFC hydrocarbon requirement. For example, a 2%
drop in H.sub.2 product concentration, e.g., from 21% to 19%, would
correspond to an increase in CH.sub.4 concentration of 1%, or an
increase in C.sub.2H.sub.6 concentration of 0.67%, or some
intermediate combination of each. A decrease in H.sub.2
concentration of more than 1% would indicate that the reformate is
no longer suitable for SOFC feed, all other factors related to
H.sub.2 production being the same. Consequently, only small
differences in catalyst selectivity for H.sub.2 production can
result in large differences in the performance of a downstream SOFC
device, so even a small performance enhancement, for example, from
20% to 20.5%, has significance.
[0054] TABLE 1 following contains the test results for several
catalysts of the present invention, compared with those from a 1
wt. % Rh/Al.sub.2O.sub.3 control catalyst:, showing the amount of
hydrogen in the reformate product after 2 hours reaction time:
TABLE-US-00002 TABLE 1 % H.sub.2 (after 2 hr) % H.sub.2 (after
(ATR, H.sub.2O/ Catalyst Metals 2 hr) (POX) HC = 1:5) C-1 1% Rh
(Control) 20.2 20.3 I-1 2% Ir--2% Ni 19.1 20.3 I-2 1% Pd--5% Ni
19.9 20.7 I-3 2% Ir--2% Ni, 20.5 21.3 5% Pt first stage I-4 1%
Pd--5% Ni, 20.8 21.6 5% Pt first stage
[0055] As shown by the results in TABLE 1, the Ir--Ni catalyst I-1
and the Pd--Ni catalyst I-2 showed similar POX and ATR performance
compared to control catalyst C-1 containing 1 wt. % Rh. In the ATR
process just described, the H.sub.2O:HC ratio was 1:5.
[0056] Catalysts I-3 and I-4 are analogous to catalysts I-1 and
I-2, respectively, but each further includes a first stage
comprising 5 wt. % Pt. In these dual stage test catalysts, the
first stage had a length of 1/8 inch, the second stage a length of
1 inch (cf. FIG. 1).
[0057] As shown by the data in TABLE 1, the two-stage configuration
of catalysts I-3 and I-4 produced a significant improvement in
hydrogen generation than their single-stage counterparts,
especially in the water-containing ATR process. In addition, the
dual stage catalysts of the present invention showed improved
stability.
[0058] TABLE 2 following contains hydrogen production test data for
a 2% Ir-2% Ni/La.sub.2O.sub.3 second-stage catalyst I-5, along with
results for dual stage catalysts I-6 and I-7 containing,
respectively, 5% Pt and 10% Ir first-stage catalysts. The use of
the first-stage Pt-containing catalyst I-6 enhanced the hydrogen
concentration from below 18.1% to about 20.5%. The use of the
first-stage Ir-containing catalyst I-7 also led to an enhancement
of hydrogen concentration compared with the I-5 single stage
catalyst, although it was slightly lower than that obtained with
the Pt catalyst. The use of Ir in the catalyst is of interest
because it is much less expensive than Pt. Possible improvements in
the performance of the Ir-containing first stage catalyst are
possible through optimization. TABLE-US-00003 TABLE 2 First-stage
Second-stage Catalyst metals metals % H.sub.2 (after 2 hr) I-5 None
2% Ir--2% Ni 18.1 I-6 5% Pt 2% Ir--2% Ni 20.5 I-7 10% Ir 2% Ir--2%
Ni 19.8 I-8 5% Pt 5% Ni 19.6 1-9 None 1% Pd--5% Ni 20.3 1-10 5% Pt
1% Pd--5% Ni 21.0
[0059] Dual stage catalyst I-8, which includes a 5% Pt first-stage
and a 5% Ni second stage catalyst, also gave improved hydrogen
production relative to single stage catalyst I-5.
[0060] A Ni-only catalyst cannot be used as a POX catalyst because
it is hard to light off, and carbon deposition on catalyst presents
a serious problem. If a Pt catalyst is put in front of it, the
Ni-only catalyst can light off but degrades very quickly, most
likely because of coke deposition. However the degradation problem
is overcome by inclusion of a small amount of a metal such as Pt,
Pd, Ir, Au, or Rh in the Ni catalyst, which results in the activity
of the catalyst being maintained.
[0061] Modifying the Ni-containing second-stage catalyst I-8 by the
addition of Pd to give catalyst I-9 resulted in an increase in
hydrogen concentration. Addition of a 5% Pt first-stage catalyst to
catalyst I-9, resulting in catalyst I-10, resulted in a further
increase in hydrogen concentration.
[0062] The data in TABLE 3 following represent hydrogen production
data obtained with 1% Pd-5% Ni catalyst I-11 comprising a foam
substrate. Inclusion of 0.5 wt. % Rh in I-11 to give catalyst I-12
resulted in a substantial enhancement in hydrogen concentration.
TABLE-US-00004 TABLE 3 Catalyst * Metals % H.sub.2 (after 2 hr)
1-11 1% Pd--5% Ni 19.9 1-12 0.5% Rh--1% Pd--5% Ni 21.1 * Catalysts
were aged for 10 hr at 1200.degree. prior to testing
[0063] TABLE 4 following contains comparative hydrogen production
data for 2% Pd-5% Ni catalyst I-13 and 0.5% Rh-1% Pd-5% Ni catalyst
I-14, both comprising a monolith substrate, showing the amount of
hydrogen in the reformate product after reaction times of 2 hours
and 5 hours. At the shorter reaction time, both catalysts yielded a
similar concentration of hydrogen. At the longer reaction time,
however, the hydrogen concentration from catalyst I-13 underwent a
substantial decrease, while that from the Rh-containing catalyst
was substantially unchanged. The Rh--Pt--Ni combination in catalyst
I-15 produced the highest hydrogen concentration in the
product.
[0064] Thus, in addition to its beneficial effect on hydrogen
generation, the inclusion of a small amount of Rh in the catalyst
of the present invention resulted in improved durability,
presumably as a consequence of improved resistance of the catalyst
to sulfur poisoning and coke formation. TABLE-US-00005 TABLE 4 %
H.sub.2 % H.sub.2 Catalyst * Metals (after 2 hr) (after 5 hr) I-13
2% Pd--5% Ni 21.3 19.9 I-14 0.5% Rh--1% Pd--5% Ni 21.3 21.2 I-15
0.5% Rh--1% Pt--5% Ni 22.0 22.0 * Catalysts were aged for 10 hr at
1200.degree. prior to testing
[0065] While the invention has been described by reference to
various specific embodiments, it should be understood that numerous
changes may be made within the spirit and scope of the inventive
concepts described. Accordingly, it is intended that the invention
not be limited to the described embodiments, but will have full
scope defined by the language of the following claims.
* * * * *