Removal of CO, hydrocarbons and NO.sub.x with catalyst containing platinum rhodium

A method for treating a gas comprising carbon monoxide, hydrocarbons and nitrogen oxides, comprising the step of:

• catalytically oxidizing carbon monoxide and hydrocarbons present in the gas, and catalytically reducing nitrogen oxides present in the gas, in the presence of a catalyst composition comprising;
• a refractory body having a plurality of substantially parallel passages extending therethrough, the passages being defined by walls, and
• a catalytic material disposed on the walls, the catalytic material comprising a catalytic coat, and the catalytic coat comprising,
• from 0.45 to 2.0 g/in.sup.3 the catalyst composition of a co-formed rare earth oxide-zirconia support material wherein there is 2 to 30 weight percent rare earth oxide based on the weight of rare earth oxide plus zirconia, and having a first rhodium catalytic component dispersed thereon to catalyze the oxidation of carbon monoxide and catalyze the reduction of nitrogen oxides, and
• an alumina support material having a platinum catalytic component dispersed thereon to catalyze the oxidation of carbon monoxide and hydrocarbons,
• wherein the total rhodium catalytic component is present at from about 0.1 g/ft.sup.3 to 15 g/ft.sup.3 of catalyst composition and the total platinum catalytic component is present at from 5 to 100 g/ft.sup.3 of the catalyst composition.