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

Oxygen mobility on Pd/Al 2 O 3 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 CO 2 produced during, for example, methane oxidation, more rapidly than from O 2 molecules. The oxygen exchange from C 18 O 2 occurs mainly on Al 2 O 3 , whereas 18 O 2 exchange needs to be carried out in the presence of palladium. However, the presence of Pd on Al 2 O 3 slightly enhances C 18 O 2 exchange according to the number of exchanged atoms in the gas phase. In this case, the calculation of initial rate for C 18 O 2 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.