Article révisé par les pairs
Résumé : The interaction of 0 / 0 2 mixtures with well defined small Pd particles on different support materials (mica, MgO, alumina) has been studied by means of SSIMS. Various ionic species are desorbed from the surface, including tho. e of the type PdnX + (X = C, 0 , CO; n = 1, 2). Under catalytic reaction condition at total pres ures below 10 - 4 Pa the relative intensities Pd nX+/ Pd ; depend on the partial pressures of CO and O2 on the surface temperature and on the Pd particle size. Our results indicate the partial decomposi tion of CO and the formation of surface carbon as an intermediate species during the steady state CO2 production. The intermediate carbon formation is most pronounced for small Pd particles (3 nm) at high CO parlial pressures. Minor amounts of carbon are found for continuous films. The observed particle siz.e effect proves the CO oxidation over Pd to be structure sen itive.