Patent GB-1398893-A (GB)
Title: Method of treating exhaust gases of internal combustion engines
IPC: B01D53/86
Filed: 1972-06-09
Abstract: 1398893 Purifying internal combustion engine exhaust gases W R GRACE & CO 9 June 1972 [11 June 1971] 27087/72 Heading F1B [Also in Divisions B1 and B2] Noxious components of the exhaust gas of an internal combustion engine are converted into less harmful entities by a method wherein the exhaust gas is contacted with a catalytic body comprising a monolith upon which is supported a catalytic component effective to catalyse the conversion of the noxious components, the monolith comprising a core of ceramic material capable of withstanding a temperature of 1800F coated with a composition comprising transitional alumina and at least one rare earth metal oxide, the composition containing from 0.1 to 10 parts by weight of rare earth metal oxide per 100 parts by weight of transitional alumina. The ceramic material from which the core is made may be alpha-alumina, magnesiaalumina spinel, mullite, zircon-mullite or cordierite; the core may be made by the procedure disclosed in Specification No. 1349400. The transitional alumina may be gamma-alumina; reference also is made to other transitional forms, namely chi, kappa, eta, theta and delta. The composition may contain oxide of rare earth metal or metals selected from scandium, yttrium and elements of atomic number 57 to 71 inclusive. The monolith may be prepared by a procedure wherein the core is coated with an aqueous slurry containing transitional alumina, dried to remove the water of the slurry and, optionally, calcined at a temperature below that temperature at which the transitional alumina is converted to alpha-alumina, rare earth metal salt(s) decomposable on heating to the oxide(s) either being present in the slurry (for example by the use of pre-prepared rare earth metal salt(s)-impregnated transitional alumina) or being composited with the dried coated core by impregnation from solution followed by removal of solvent of the solution from the impregnated coated core, the rare earth metal salt(s)-containing coated core being heated, at some stage during the procedure, at a temperature at which the salt(s) decompose to the oxide(s); reference also is made to the preparation of the monolith by a procedure wherein the core is immersed in a slurry containing alumina trihydrate, carboxymethyl cellulose and rare earth metal salt, shaken and  sprayed with air to remove excess slurry, dried and calcined to convert the alumina trihydrate to gamma-alumina, the gamma-alumina and rare earth metal oxide constituting 10-12 weight per cent of the monolith. The catalytic component, which may constitute from 0.1 to 70 weight per cent of the catalytic body, may be a single substance or two or more substances; specified catalytic components are (i) palladium plus oxides of copper and chromium, (ii) palladium plus oxides of copper and manganese, (iii) palladium plus oxides of copper, chromium and manganese, (iv) oxides of copper, chromium and manganese in combination, (v) oxides of copper, manganese, iron and cobalt in combination and (vi) platinum alone. Exemplified catalytic bodies comprise oxides of copper, chromium and manganese in combination or platinum alone supported on a cylindrical honeycombed porous ceramic alpha-alumina core (prepared by the procedure disclosed in Specification No. 1349400) and oxides of copper, chromium and manganese in combination supported on a core of spinel or mullite or zircon-mullite or cordierite, the core in each case being coated with a composition comprising gamma-alumina and oxides of lenthanum, cerium, praseodymium, neodymium and samarium derived from a slurry containing rare earth metal-stabilized gamma-alumina and carboxymethyl cellulose.