Ceria as a new support of noble metal catalysts for hydrocarbon reactions: chemisorption and catalytic studies
Metal/cerium-oxide systems were practically not studied in hydrocarbon reactions. Chemisorption properties—in temperature programmed reduction, hydrogen adsorption, and H2/O2 titration—and catalytic behavior of ceria-supported Pt and Rh catalysts with different metal loadings and with two pre-reduction temperatures (LTR, TR=573 K and HTR, TR=773 K) were investigated. Pt/CeO2 was tested in transformation of n-hexane while Rh/CeO2 in ring opening of methylcyclopentane (MCP). Higher spillover activity was found for the LTR Rh samples than for HTR ones. The opposite was true for Pt. The Rh/ceria samples showed ordinary catalytic behavior: structure insensitivity was observed for the first CC bond cleavage of MCP on Rh/ceria and the further reaction of the ring opening intermediates was affected by the surface hydrogen concentration. The Pt/LTR samples showed catalytic properties similar to EUROPT-1, while the HTR samples were different, namely the higher spillover activity caused high C5-cyclization selectivity on the catalyst with low metal loading, and surprisingly high hydrogenolysis selectivity on that with higher metal loading.