Reactivity of non-continuous Rh model catalysts deposited on differently oriented Al2O3 substrates

The CO oxidation on small Rh particles deposited on a single crystal alumina support has been studied by means of the molecular beam technique using the transient method at temperatures between 290 and 530 K. The surface is predosed with a defined exposure of oxygen and then exposed to the beam of carbon monoxide at a given temperature until the reaction is complete. The temperature and Rh coverage dependent CO oxidation data were obtained for three pairs of samples with the substrate crystallographic orientations (0 0 0 1), (1 1̄ 0 2), (1 1 2̄ 0). The influence of substrate orientation as well as Rh particle size and density upon the CO oxidation has been investigated. The substrate orientation does not seem to affect the CO oxidation rate whereas a significant increase of CO oxidation rate with decreasing Rh particle size has been observed. The rate reached its maximum at the temperature of about 430 K independently on the substrate structure as well as on the Rh particle size.