CATALYSTS FOR THE OXIDATION OF SOOT FROM DIESEL EXHAUST-GASES .1. AN EXPLORATORY-STUDY

A large number of candidate soot oxidation catalysts were screened on their catalytic activity with a model soot. It was found that the inte nsity of contact between soot and catalyst is one of the major paramet ers that determine the soot oxidation rate. Two types of contact were studied; many catalysts increase the rate of soot oxidation considerab ly when the contact is intimate ('tight'), whereas under conditions of poor ('loose') contact only some catalysts accelerate this oxidation reaction. It is tentatively suggested that (i) mobility of the catalys t is a major parameter determining the loose contact activity of catal ysts and (ii) this mobility correlates with the melting point or the p artial pressure of the catalyst.