Size effects in C2H4 dehydrogenation studied by HR-PES: Pt(111) versus Pt/CeO2/Cu(111) model catalysts

Complex catalysts consisting of noble metal particles on reducible CeO2 supports show unique reactivity and reduced carbon precipitation during hydrocarbon reforming. In order to explore these effects at the microscopic level, we have studied the adsorption and dehydrogenation of C2H4 on a Pt/CeO2(111)/Cu(111) and Pt(111)model catalysts. Reaction and decomposition of C2H4 are investigated by means of HR-PES as a function of the CeO2-x stoichiometry and Pt particle size. In contrast to the behavior on Pt(111), where molecular adsorption of C2H4 is observed, dissociation intermediates, namely CCH3 and CHCH3, were found on the Pt nanoparticles even at 100 K. The dehydrogenation of these products to carbonaceous deposits is accompanied by the hydrogen spillover and formation of hydroxyl groups on ceria. The decomposition of the hydroxyl groups and desorption of H2 occurs at 450 K. At higher temperatures, carbonaceous species react with oxygen, which is supplied via reverse spillover from the ceria and, subsequently, desorb in the form of CO and/or CO2.