Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1989-12-08
1991-09-24
Shine, W. J.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502310, 4232132, B01J 2104, B01J 2310, B01J 2314, B01J 2322, B01J 2326, B01J 2372, B01J 2382, B01J 2386
Patent
active
050513931
DESCRIPTION:
BRIEF SUMMARY
This invention relates to catalyst compositions for use primarily as vehicle exhaust gas catalysts, to control the emissions of noxious gases, particularly carbon monoxide, urburnt hydrocarbons and/or nitrogen oxides, but also having utility in other fields where similar emission control is necessary.
Catalytic converters currently in use in motor vehicles to control exhaust gas emissions generally comprise one or more platinum group metals, e.g. platinum, palladium, rhodium or rhenium, alone or in combination, and thus tend to be expensive. The most commonly used catalytic material is platinum on alumina. Much research has been carried out to find a less expensive alternative, and one system that has received considerable attention is the SnO.sub.2 -Cr.sub.2 O.sub.3 system. For example, in a series of papers: (0.1-1 mole %) of Cr.sub.2 O.sub.3 is a very active catalyst for the adsorption and reduction of nitric oxide (NO) at low temperatures (150.degree.-400.degree. C.) in the presence of a reducing gas such as CO, H.sub.2 or C.sub.2 H.sub.4. The catalyst is prepared by reacting HNO.sub.3 with metallic tin to produce SnO.sub.2 which is recovered, dried at 120.degree. C. and further heated at 350.degree. C. for 3 hours and 500.degree. C. for a further five hours. The SnO.sub.2 is then suspended in water and Cr.sub.2 O.sub.3 added to the suspension with continuous stirring over a long period until a homogenous dispersion is obtained. The suspension is then dried, heated at 350.degree. C. for 5 hours and finally calcined in air at 900.degree. C. for 5 hours. As a result an SnO.sub.2 catalyst is obtained having higher valency chromium ions (average valency 3.85) stabilised in the surface layer.
SnO.sub.2 -Cr.sub.2 O.sub.3 catalysts are also reported to be effective catalysts for the catalytic oxidation of CO in gaseous mixtures containing SO.sub.2 (USSR Patent No. 736,997); catalytic removal of SO.sub.2 (USSR Patent No. 691,185); catalytic reduction of nitrogen oxides in the presence of NH.sub.3 (Japanese published patent application No. 75-108169); and as alkylation catalysts in the alkylation of phenols (U.S. Pat. No. 4,208,537). In USSR Patent 736,997 such SnO.sub.2 -Cr.sub.2 O.sub.3 catalysts are prepared by heating SnCl.sub.2 and CrO.sub.3 in relative proportions to give SnO.sub.2 :Cr.sub.2 O.sub.3 mole % ratios of from 1:99 to 99:1. In Japanese published patent application 75-108169, the SnO.sub.2 -Cr.sub.2 O.sub.3 catalysts are prepared by coprecipitation from an aqueous solution containing concentrated HCl, CrO.sub.3 and SnCl.sub.2.2H.sub.2 O by addition of NH.sub.4 OH. The mixed oxide precipitated was recovered, slurried in water, coated onto an alumina support, dried and calcined. In U.S. Pat. No. 4,208,537, the SnO.sub.2 -Cr.sub.2 O.sub.3 containing alkylation catalysts are prepared by coprecipitation, or kneading preformed SnO.sub.2 and Cr.sub.2 O.sub.3 -containing gels to form an oxide mixture and calcining, optionally after coating onto a suitable, e.g. alumina, support.
More recently it has been found (published UK Patent Application No. 2,194,174) that catalyst compositions having high levels of catalytic activity in the oxidation of CO and unburnt hydrocarbons, and in the catalytic reduction of nitrogen oxides, equivalent in many cases to those of precious metal catalysts and therefore potentially useful as vehicle exhaust gas catalysts for the control of noxious emissions, are obtained by impregnating tin(IV) oxide (SnO.sub.2) with chromium(VI) oxide (CrO.sub.3) and calcining the resulting product. For convenience the catalyst may be regarded as a mixed SnO.sub.2 :CrO.sub.3 catalyst. In such catalysts the tin:chromium weight ratio (calculated as SnO.sub.2 :CrO.sub.3) may be in the range 99:1 to 1:99, but is preferably in the range 24:1 to 2:3, most preferably 4:1 to 2:3.
The SnO.sub.2 :CrO.sub.3 catalyst composition is preferably obtained by impregnating tin(IV) oxide, preferably uniformly dispersed on a high surface area ceramic support such as cordierite, and deposited thereon by the sol-g
REFERENCES:
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An abstract of the above Japanese Patent was submitted by applicants.
"The Catalytic Reduction of Nitrous Oxide by Carbon Monoxide over TinIV Oxide", M. J. Fuller et al., 11/11/75, vol. 39, pp. 412-418.
"Catalysis of the NO-CO Reaction: A Further Example of Synergism in the PD-SNO Systems"; Martin J. Fuller, 1976, pp. 787-788.
Water Promoted Oxidation of Carbon Monoxide over Tin IV Oxide Supported Palladium; E. Hincks et al., 10/13/77, vol. 269, pp. 585-586.
Adsorptions Reduction of NO on Tin IV Oxide Doped with Chronium III Oxide, F. Solymosi et al., 11/1/77, pp. 42-51.
"Oxidation of Ethylene Oxide and Propylene on SnO.sub.2 O-Cr.sub.2 O.sub.3 " Bozso, F., Symposium on the Mechanisms of Hydrocarbon Reactions 7/73, pp. 311-320.
Chemical Abstracts, VI. 91, 1979 Abstract No. 97262b, "The Preparation and Activation of Tin IV Oxide-Chromium III Oxide Catalyst".
Chemical Abstracts, vol. 81, 1974, Abstract No. 175627j, "Removing Nitrogen Oxides from Waste or Exhaust Gases by Contacting with Amonia in the Prescence of Tin Oxide of Cerium Oxide";
"The Catalytic Reduction of Nitric Oxide by Carbon Monoxide SnO.sub.2 CuO Gels"; J. J. Fuller et al.; 8/4/75; vol. 42, pp. 418-424.
Harris Peter J. F.
Harrison Philip G.
Shine W. J.
TI Corporate Services Limited
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