An engine exhaust catalyst containing precious metal nanoparticles is promoted with bismuth. The bismuth promotion improves the catalyst's CO oxidation performance. Also, by varying the amount of bismuth that is added, the NO conversion rate that can be realized with the catalyst can be controlled. The control over the NO conversion rate is important because the passive regenerative performance of a particulate filter used in engine exhaust systems is based on the amount NO.sub.2 that is present in the exhaust stream that reaches the particulate filter. The amount of NO.sub.2 being produced needs to be optimized (not necessarily maximized) so that adequate particulate filter regeneration performance can be maintained while avoiding unused, toxic NO.sub.2 from being exhausted into the atmosphere.