Activation and Catalytic Dehydrogenation of Methane on Small Pdx+ and PdxO+ Clusters

The temperature-dependent. adsorption as well as. the possible activation and dehydrogenation of methane mediated by small free palladium Pd-x(+) (x = 2-4) palladium mono-oxide : PdxO+ (x = 2-4) clusters have been studied in an ion trap experiment under multicollision conditions. The smallest clusters Pd-2(+) and Pd-3(+) are found to readily dehydrogenate methane, while Pd-4(+) is completely nonreactive within the whole investigated temperature range between 220 and 300 K. In case of the oxides PdxO+, a critical number of at least three coadsorbed CD4 is required before methane dehydrogenation can be observed. Temperature-dependent kinetic studies of the reaction of Pd-2(+) and Pd2O+ with methane allow for the determination of catalytic reaction mechanisms that involve C-D bond cleavage and C-C bond formation processes. The catalytic activity of these two clusters compared terms of active species, cooperative effects, and activation barriers. Finally, the possible methane oxidation on PdxO+ is discussed.