VEHICLE EXHAUST CATALYSIS .1. THE RELATIVE IMPORTANCE OF CATALYTIC-OXIDATION, STEAM REFORMING AND WATER-GAS SHIFT REACTIONS

The activity of a monolithic three-way catalyst has been compared with the performance of the individual metals (Pt, Pd, Ph) for oxidation, steam reforming and water-gas shift. The presence of ceria was found t o accelerate the last two reactions. The orders of activity were found to be: oxidation - presence or absence of ceria, Pt > Pd > three-way > Ph; steam reforming - no ceria in the catalysts, Pd > Ph > Pt; steam reforming - ceria in the catalyst, three-way similar to Ph > Pd > Pt; water-gas shift - no ceria, Pd > Pt > Ph; water-gas shift - ceria, th ree-way > Pt > Pd > Ph. Both the water-gas shift and the steam reformi ng reactions became significant only at higher temperatures than those needed to facilitate oxidation. As a result, both reactions are proba bly important only after oxygen has been exhausted in the monolithic b ed.