Three-way catalysts for purification of exhaust gas and method for the preparation of the catalysts

Claim 1

A three-way catalyst suitable for the purification of exhaust gas from an internal combustion engine in a motor vehicle, the catalyst comprising: a. a monolithic substrate through which exhaust gas may flow, b. a refractory oxide layer deposited on the substrate, c. at least one platinum group metal component selected from the group consisting of platinum, rhodium and palladium, and d. a tungsten component selected from the group consisting of tungsten metal and a tungsten-containing compound the amount of platinum group metal present being from 300 to 3500 g per m 3 of the volume of the monolithic substrate with the refractory oxide layer deposited thereon, the amount of tungsten present being at least from 2650 to 22,000 g per m 3 of said volume of substrate and deposited oxide layer, and the weight ratio of tungsten to platinum group metal being from 2.3 to 18.8:1, the catalyst being further characterized by its ability to oxidize carbon monoxide and hydrocarbon, and to reduce nitrogen oxides with a reduced tendency to form ammonia.

Claim 11

A method for the preparation of a three-way catalyst comprising: (a) depositing a refractory oxide layer on a monolithic substrate; (b) depositing on the refractory oxide layer a catalyst component which comprises at least one platinum group metal selected from the group consisting of platinum, rhodium and palladium and wherein the amount of platinum group metal deposited is from 300 to 3500 g per m 3 of the volume of the monolithic with the refractory layer deposited thereon; (c) before or after deposition, associating a tungsten-containing compound with the said refractory oxide and/or the said one or more platinum group metals wherein the amount of tungsten moiety associated is from 2650 to 22,000 g per m 3 of the volume of the monolith substrate with the refractory layer deposited thereon and the weight ratio of tungsten to platinum group metal is from 2.3 to 18.8:1.

Claim 12

A method for the preparation of a three-way catalyst comprising: (a) depositing a refractory oxide layer on a monolithic substrate; (b) depositing on the refractory oxide layer a catalyst component which comprises at least one platinum group metal selected from the group consisting of platinum, rhodium and palladium and wherein the amount of platinum group metal deposited is from 300 to 3500 g per m 3 of the volume of the monolithic with the refractory layer deposited thereon; (c) before or after deposition, associating a tungsten-containing compound with the said refractory oxide and/or the said one or more platinum group metals wherein the amount of tungsten moiety associated is from 2650 to 22,000 g per m 3 of the volume of the monolith substrate with the refractory layer deposited thereon and the weight ratio of tungsten to platinum group metal is from 2.3 to 18.8:1.