Exhaust gas treatment catalyst

A method of preparing a catalyst composition, the method comprising:

• dissolving a salt of at least one promoter metal in an aqueous-based metal oxide sol, wherein the salt of the at least one promoter metal dissociates in the aqueous-based metal oxide sol to form an aqueous-based metal salt/metal oxide sol mixture, wherein the metal oxide particles comprise one or more oxides of a transition metal or lanthanide of Group 3 or Group 4 of the Periodic Table;
• treating ammonium or proton exchanged small-pore molecular sieve particles having a pore structure and a maximum ring size of eight tetrahedral atoms with the aqueous-based metal salt/metal oxide sol mixture to allow impregnation of the promoter metal into the pore structure of the small-pore molecular sieve;
• and
• drying and calcining the treated small-pore molecular sieve particles to form the catalyst composition, wherein the catalyst composition comprises the small-pore molecular sieve particles impregnated with the promoter metal, and metal oxide particles dispersed within the small-pore molecular sieve particles and external to the pore structure of the small-pore molecular sieve particles.