Isotopic Oxygen Exchange over Pd/Al2O3 Catalyst: Study on C18O2 and 18O2 Exchange

Abstract

Oxygen mobility on Pd/Al2O3 catalysts is generally considered to be rather slow compared with other noble metal catalysts. This study shows that oxygen can be exchanged from gas-phase CO2 produced during, for example, methane oxidation, more rapidly than from O2 molecules. The oxygen exchange from C18O2 occurs mainly on Al2O3, whereas 18O2 exchange needs to be carried out in the presence of palladium. However, the presence of Pd on Al2O3 slightly enhances C18O2 exchange according to the number of exchanged atoms in the gas phase. In this case, the calculation of initial rate for C18O2 exchange is not adequate to evaluate oxygen mobility; information on the number of exchanged atoms and on the evolution of the concentrations of the different isotopomers is also needed. The enhancement of oxygen exchange is due to carbonate formation on the catalytic surface, as evidenced by in situ FTIR spectroscopic measurements. A five-step mechanism is suggested to explain these findings. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.