Abstract: A preferred catalytically active solid acid material, zeolite, forms the basis of a washcoat effective for treating diesel-fueled engine exhaust to reduce emission of particulate. In a preferred method, hydrocarbon in exhaust is cracked and oxidized in the presence of a zeolite/silica washcoat mixture catalyzed with precious metal. A preferred Y-type zeolite provides acidic (cationic) sites having releasable cations which are exchanged with precious metal to form catalyzed zeolite. A preferred method of making the catalyzed zeolite/silica washcoat is provided, whereby colloidal silica is disposed as a barrier over the catalyzed washcoat, limiting exposure of catalyst to sulfur constituents in the exhaust.