Catalyst for purifying the exhaust gases of internal combustion engines and method for making the catalyst

A method for making a catalyst for purifying the exhaust gases of internal combustion engines, comprising:

• (a) providing aluminum oxide of the transition series as a carrier,
• (b) adding to said aluminum oxide as promoter for catalysis 3-70% by weight CeO.sub.2, 0-20% by weight La.sub.2 O.sub.3, 1-20% by weight ZrO.sub.2, 0-10% by weight Fe.sub.2 O.sub.3, and 0-20% by weight NiO.
• (c) subsequently treating said carrier in air at 300.degree.-900.degree. C.,
• (d) applying to said carrier a catalytically active phase by impregnating said carrier, said active phase comprising 0.02-3% by weight of at least one member selected from the group consisting of platinum, palladium, and rhodium;
• wherein said catalyst contains at least one base metal from the group consisting of lithium, potassium, rubidium, magnesium, calcium, barium, lanthanum, cerium, praseodymium, neodymium, samarium, and iron, in an amount of up to 5 times the total mass of the noble metal and is introduced by impregnating the promoter-containing carrier with a solution (A) of compounds of platinum, palladium or platinum and palladium in an amount corresponding to at least 30% of the total mass of platinum, palladium or platinum and palladium, drying and activating, then impregnating with a solution (B) which contains the compound of rhodium and optionally the residual amount of platinum, palladium or platinum and palladium, drying and activating wherein said solution (B) contains one or more base-metal compounds.

A catalyst for purifying the exhaust gases of internal combustion engines, consisting essentially of:

• aluminum oxide of the transition series as carrier,
• 3-70% by weight CeO.sub.2, 0-20% by weight La.sub.2 O.sub.3, 1-20% by weight ZrO.sub.2, 0-10% by weight Fe.sub.2 O.sub.3, and 0-20% by weight NiO as promoter,
• and with a catalytically active phase applied to said carrier, said active phase comprising 0.02-3% by weight of at least one member selected from the group consisting of platinum, palladium, and rhodium, wherein said carrier is optionally lattice-stabilized, and wherein said catalyst contains at least one base metal from the group consisting of lithium, potassium, rubidium, magnesium, calcium, barium, lanthanum, cerium, praseodymium, neodymium, samarium, and iron, in an amount of up to 5 times the total mass of the noble metal,
• said catalyst being made by a method comprising impregnating said carrier with a solution of said promoter compound, or coating said carrier by means of mixing with a suspension of an oxide, hydroxide or carbonate of said promoter, or impregnating with a solution of said promoter compound and coating by mixing with a suspension of an oxide, hydroxide or carbonate of said promoter, subsequently treating said carrier in air at 300.degree.-900.degree. C. and then impregnating with a solution of compounds of the noble metals, drying and activating the impregnated carrier obtained thereby, at a temperature in a range of 250.degree.-1050.degree. C., whereby said catalyst contains at least one base metal from the group consisting of lithium, potassium, rubidium, magnesium, calcium, barium, lanthanum, cerium, praseodymium, neodymium, samarium, and iron, in an amount of up to 5 times the total mass of the noble metal and is obtained by impregnating the promoter-containing carrier with a solution (A) of compounds of platinum, palladium or platinum and palladium in an amount corresponding to at least 30% of the total mass of platinum, palladium or platinum and palladium, drying and activating, whereby a large part of said platinum, palladium, or platinum and palladium remains removed from the vicinity of said base metals, then impregnating with a solution (B) which contains a compound of rhodium and optionally the residual amount of platinum, palladium or platinum and palladium, drying and activating, wherein said solution (B) contains one or more base-metal compounds.