Described is a catalyst composition suitable for use as a selective catalytic reduction catalyst, including small-pore molecular sieve particles having a pore structure and a maximum ring size of eight tetrahedral atoms and impregnated with a 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, wherein the metal oxide particles include one or more oxides of a transition metal or lanthanide of Group 3 or Group 4 of the Periodic Table. A method for preparing the catalyst, a method for selectively reducing nitrogen oxides, and an exhaust gas treatment system are also described.