(560do) Investigation of Ceria, Vanadia/Ceria and Gold/Ceria Catalysts By Operando Raman-Online FTIR during Toluene Oxidation

Luo, Y., Hong Kong University of Science and Technology
Wang, Q., The Hong Kong University of Science and Technology
Yeung, K. L., The Hong Kong University of Science and Technology
Bañares, M. A., The Institute of Catalysis and Petrochemistry
Toluene oxidation on three ceria catalysts, CeO2, VOx/CeO2 and Au/CeO2, was investigated by an operando Raman-online FTIR reactor cell. The reactive surface oxygen sites were preferred sites for vanadium and gold deposition. The deposited vanadium existed as V5+, while most of the gold was in Au+ state and roughly a third of ceria was in the reduced Ce3+ state. The Au/CeO2 and CeO2 catalysts (T50*=260 and 290°C) were more active and selective toward the complete oxidation of toluene than VOx/CeO2 catalyst (T50*=370°C), where T50* refers to the temperature for 50% of CO2 yield. The η2-peroxide O22-adswas detected on Au/CeO2 and CeO2 catalysts, where toluene molecules preferentially adsorbed parallel to the surface via π-bonding. Au/CeO2 gave complete combustion producing mainly CO2. On the other hand, η1-superoxide O2-ads was found on VOx/CeO2 catalyst and the toluene molecule adsorbed via σ-bonding forming carbenium ions on the vanadia Brønsted acid sites. This catalyst produced significant amount of benzaldehyde as partial oxidation byproduct and CO (< 25%). The nature of the active sites, configurational adsorption of toluene and the reactive oxygen species play an important role in the catalyst activity and selectivity leading to a large contrast in the catalytic behavior of the CeO2, VOx/CeO2 and Au/CeO2 catalysts.