THE EFFECT OF PARTICLE-SIZE ON NITRIC-OXIDE DECOMPOSITION AND REACTION WITH CARBON-MONOXIDE ON PALLADIUM CATALYSTS

The effect of palladium particle size on its catalytic activity was investigated by the decomposition of chemisorbed nitric oxide and the reaction of nitric oxide with carbon monoxide in flow conditions. Palladium particles (30-500 angstrom) were prepared on silica thin films (100 angstrom) which were supported on a Mo(110) surface. The reactivity of the supported palladium varied with the metal particle size. On large palladium particles, nitric oxide (NO) reacts to form nitrous oxide (N2O), dinitrogen (N2) and atomic oxygen during temperature-programmed reaction, whereas on small particles (< 50 angstrom), nitrous oxide is not formed. Similarly, reactions of NO with CO on large particles, in flow conditions produce N2O, N2 and CO2, whereas N2O is not produced on small particles. In addition, more extensive NO decomposition is observed on the smaller particles.