FTIR investigation under reaction conditions during CO oxidation over Ru(x)-CeO2 catalysts

Abstract

New insight on the understanding of the reaction mechanisms during the CO oxidation over Ru-containing CeO2 catalysts was reported. A set of ruthenium high surface area CeO2 oxides, with two different Ru loadings, was prepared for studying the evolution of Ru and Ce species during CO oxidation reaction, using a reaction mixture of 1 % CO, 0.5 % O2, N2 balance and a contact time W/FCO = 7.4 gcat h molCO−1. The samples were characterized by SBET, XRD, DRS UV–vis, TPR, Raman spectroscopy, and XPS. Furthermore, the samples were investigated by FTIR measurements during CO oxidation under reaction conditions. The catalysts with low Ru loading (1.5 wt.%) presented higher catalytic activity than those containing a higher Ru loading (3 % wt.). The catalytic activity test results strongly depend on electronic changes observed at the interface/surface of ceria support. The characterization results and FTIR investigation during CO oxidation show that the presence of ruthenium species modifies the electronic properties of the ceria surface promoting a change at their surface where a redox-mechanism was detected. This causes the formation of surface oxygen vacancies which promotes oxygen mobility from the ceria lattice contributing to the CO oxidation. The ruthenium incorporation drastically favors the CO adsorption (carbonyl and dicarbonyl species). However, our FTIR data not shown a direct correlation between the ruthenium-carbonyl species (linear and bridged form) on the CO transformation. Further, the presence of ruthenium enhances the formation of surface oxygen vacancies, which favor the oxygen mobility from the ceria lattice toward the CO oxidation. It was found that at low temperatures (close down to the maximum conversion), the CO oxidation preferably happened on oxygen vacancy sites.