Steady carbon formation during CO oxidation over small Pd particles: A static sims study

Abstract

The interaction of CO/O 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 those of the type Pd n X + (X = C, O, CO; n = 1, 2). Under catalytic reaction conditions at total pressures below 10 −4 Pa the relative intensities Pd n X +/Pd n + depend on the partial pressures of CO and O 2, on the surface temperature and on the Pd particle size. Our results indicate the partial decomposition of CO and the formation of surface carbon as an intermediate species during the steady state CO 2 production. The intermediate carbon formation is most pronounced for small Pd particles (3 nm) at high CO partial pressures. Minor amounts of carbon are found for continuous films. The observed particle size effect proves the CO oxidation over Pd to be structure sensitive.