Particulate filters are one of the keys to making modern diesel
engines able to meet emissions requirements. They absorb the particles that comprise the black smoke people have traditionally associated with diesels. Japan's Mitsui Mining and Smelting Co has developed a new catalyst material for particulate filters that doesn't include platinum. Silver can work as a catalyst but it can't survive the high temperatures present in exhaust gases. Mitsui has blended a metal oxide in with silver to allow it to survive temperatures up to 800° C. Mitsui is currently testing the material for its catalyzing performance.
[Source: Green Car Congress