Described is a catalytic article for the treatment of lean burn engine exhaust gas. The catalytic article comprises a honeycomb substrate having disposed thereon a washcoat containing one or more calcined platinum group metal components dispersed on a refractory metal oxide support located on the honeycomb substrate, the platinum group metal components having an average crystallite size in the range of about 10 to about 25 nm to provide a stable ratio of NO2 to NOx when the exhaust gas flows through the honeycomb substrate. Methods of treating exhaust gas from a lean burn engine and a system for the removal of pollutants from a lean burn engine exhaust gas stream containing NOx are also described.