The present invention relates to an apparatus and method for delivering molybdenum from a lubricant source into a fuel combustion system or to the exhaust therefrom. By the present invention, molybdenum from the lubricant or the fuel will interact with phosphorus, sulfur, and/or lead from the combustion products. In this manner, the molybdenum scavenges or inactivates harmful materials which have migrated into the fuel or combustion products, and which can otherwise poison catalytic converters, sensors and/or automotive on-board diagnostic devices. The present invention can also lead to improved durability of exhaust after treatment systems.