Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1999-09-09
2003-05-06
Hendrickson, Stuart L. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S327000
Reexamination Certificate
active
06559094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the preparation of catalytic material for use in the selective oxidation of carbon monoxide, to catalyst members comprising such materials and to the conditions of their use. The invention finds utility in the preparation of hydrogen-containing gas streams for use in fuel cells, which generate power by the oxidation of hydrogen.
A known strategy for the use of fuel cells involves the generation of hydrogen from carbonaceous fuels. Generally, this process involves subjecting the fuel to desulfurization, steam reforming and high- and low-temperature water-gas shift reactions. The resulting gas stream comprises significant quantities of hydrogen (H
2
), carbon dioxide (CO
2
), water (H
2
O) and about 0.5% carbon monoxide (CO). The aforesaid quantity of CO is greater than desired for fuel cell purposes, since CO is known to poison the catalyst for the fuel cell reaction. It is therefore necessary to remove some or all of the CO, e.g., by oxidizing it to CO
2
, without removing the H
2
needed to power the fuel cell. The CO must be removed or reduced to a maximum of about 10 ppm. In a prior art process known under the trade name SELECTOXO™, the product of the water-gas shift reactions is stripped of CO in a catalytic selective oxidation process that avoids oxidation of H
2
. The commercial SELECTOXO™ catalyst involved comprises from 0.3 to 0.5% platinum and 0.03% iron dispersed on alumina support tablets or pellets by wet impregnation of the alumina with a solution of platinum and iron salts. The SELECTOXO™ catalyst material was dried at not more than 125° C. because it was expected that that catalyst would be used at temperatures not higher than 125° C. and that a higher drying temperature would detrimentally affect the platinum. The catalyzed alumina tablets are typically assembled into a bed through which the feed stream is flowed.
2. Related Art
U.S. Pat. No. 3,088,919 to Brown, Jr. et al, entitled “Treatment Of Gases” and dated May 7, 1963, discloses a process for the preferential oxidation of carbon monoxide in a hydrogen-containing gas, in particular, ammonia synthesis gas. According to the disclosed process, the gas is treated with water and is then passed over a supported platinum catalyst (see col. 1, lines 34-39). The platinum is loaded at from 0.01 to 5 weight percent of the catalyst (col. 3, lines 25-27). The Patent states that the selective oxidation process may be carried out at temperatures from 60° F. to 1200° F. (15° C. to 650° C.), preferably 200° F. to 450° F. (93° C. to 232° C.) (see col. 3, lines 4-6). Example III discloses a process for oxidizing carbon monoxide using a platinum catalyst at a catalyst temperature bed in the range of 230° C. to 500° F. (110° C. to 260° C.). The inlet gas contained 1.7 percent carbon monoxide (CO) and the exit gas contained up to 4,000 parts per million CO. The pressure may be from atmospheric to 300 psig (col. 3, line 7) and the space velocity of the gas through the catalyst may be 100 to 25,000 ft
3
gas/ft
3
catalyst per hour, preferably 4,000 to 6,000 ft
3
gas/ft
3
catalyst per hour for a single-stage operation (col. 3, lines 8-17).
U.S. Pat. No. 3,216,783 to Cohn, dated Nov. 9, 1965 and entitled “Process For Selectively Removing Carbon Monoxide From Hydrogen-Containing Gases”, discloses the use of a supported platinum catalyst containing from 0.01 to 5 weight percent platinum on pelleted, powdered or granulated support material, for use in oxidizing carbon monoxide (col. 1, lines 53-62) at a reaction temperature in the range of 110° C. to 200° C. (col. 1, lines 35-42). The space velocity of the gas is in the range of from 500 to 100,000 VHSV at 70° F. (21.1° C.).
U.S. Pat. No. 4,492,769 to Blanchard et al, dated Jan. 8, 1985 and entitled “Pollution Control Catalyst For Internal Combustion Engine Exhaust System/Catalytic Converter and Process For Its Preparation”, discloses the preparation of certain platinum-containing catalysts with calcining of 300° C. (Examples 2, 3, 4, 5).
U.S. Pat. No. 5,583,087 to Slotte, entitled “Method For Impregnating Catalyst Support With Platinum”, dated Dec. 10, 1996, discloses a method for the preparation of a catalytic material that may comprise platinum dispersed on alumina by a wet impregnation technique. In accordance with the teachings of this Patent, a solution of bivalent platinum is prepared, the bivalent platinum is oxidized to Pt
+4
, e.g., by adding hydrogen peroxide or ozone, and the Pt
+4
solution is then impregnated into the support material, preferably via chemisorption. The wetted support material is then calcined at 275° C. (see col. 3, lines 29-40).
U.S. Pat. No. 4,818,745 to Kolts, entitled “Catalyst For Oxidation Of Carbon Monoxide And Process For Preparing The Catalyst”, dated Apr. 4, 1989, discloses a catalyst for the oxidation of carbon monoxide under conditions suitable for laser applications. The catalyst comprises platinum and/or palladium dispersed on alumina via impregnation. The catalyst may contain from 0.5 to 5 weight percent platinum and/or palladium (col. 4, lines 22-29). Iron is also used in the catalyst at a loading of from about 0.2 to 4 weight percent (col. 4, lines 54-57). The preparation method includes drying and calcining the wetted support material in two stages, first at temperatures of about 30° C. to about 200° C. and then in the range of from about 300° C. to about 700° C. The material is then subjected to reducing conditions by exposure to a reducing gas at a temperature of about 550° C. to 700° C. The feed gases for the carbon monoxide oxidation processes described therein are substantially free of hydrogen.
U.S. Pat. No. 4,440,874 to Thompson entitled “Catalyst Composition And Method For Its Manufacture”, dated Apr. 3, 1984, discloses a method for the preparation of a catalytic material used for the purification of exhaust gases from internal combustion engines. The catalytic material may comprise platinum and iron and is prepared using a wet impregnation technique to deposit the catalytic metals on an alumina support material. This Patent illustrates drying and calcining the wetted support material at 450° C. (col. 7, lines 57-61).
U.S. Pat. No. 4,749,671 to Saito et al entitled “Exhaust Gas Cleaning Catalyst And Process For Production Thereof”, dated Jun. 7, 1988, discloses a catalytic material useful for cleaning diesel engine exhaust gases or other exhaust gases containing combustible carbonaceous particles. The catalytic material may comprise platinum and iron supported on alumina (see col. 3, lines 40-61). The disclosed method of preparation involves impregnating alumina pellets with a solution of the catalytic metals, drying and calcining the pellets and then grinding them and forming them into a slurry for coating on a carrier. In each example, the wetted support aterial was dried and then calcined at temperatures of 500° C. or 600° C.
U.S. Pat. No. 4,621,071 to Blanchard et al, dated Nov. 4, 1996, entitled “Composite Catalyst For Treatment Of Vehicular Exhaust Gases . . . ”, discloses catalytic materials for the treatment of vehicular exhaust gases. The disclosed materials may comprise platinum and iron dispersed on a support material that may be alumina. This Patent teaches that the support material is impregnated with a solution containing the catalytic metals and is then dried and calcined at a temperature of 300° C. to 800° C. (see col. 6, lines 53-63). The catalyst is then “activated” by exposure to a reducing atmosphere at a temperature between 200° C. and 700° C. (see col. 6, lines 64-68). In Examples 3 and 4 of this Patent, impregnated alumina materials were dried at 150° C. and then activated at 350° C. In Example 6, an impregnated material was dried at 150° C. and then calcined at 350° C. in air (see col. 11, lines 13-20).
The following references address selective oxidation of carbon monoxide: U.S. Pat. No. 3,631,073 to Cohn, dated December 28, 1971; Canadian Patent 609,619 to Cohn, dated Nov. 29, 1960; Brown, Jr. et al, “Purifying
Farrauto Robert J.
Korotkikh Olga
McFarland Andrew
Engelhard Corporation
Hendrickson Stuart L.
Lindenfeldar Russell G.
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