Relativistic DFT studies of dehydrogenation of methane by Pt cationic clusters: Cooperative effect of bimetallic clusters
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The dehydrogenation reaction mechanisms of methane catalyzed by transition-metal clusters PtM+ ( M) Cu, Ag, Au) and Pt-n(+) (n = 2-4) have been investigated theoretically. In the reactions of PtM+ (M = Cu, Ag, Au) with CH4, cleavage of the first C-H bond is quite facile without barrier. The second C-H bond activation and the release of H-2 from molecular complex are generally the rate-determining steps. In the reactions of platinum clusters Pt-n(+)(n = 2-4) with CH4, the H-2 elimination from the dihydrogen complex is the ratedetermining step. Spin crossover may occur in the reaction of Pt-2(+) and CH4. Pt-2(+) and Pt-3(+) can dehydrogenate methane efficiently due to remarkable thermodynamic stability of the products. The dehydrogenation of methane induced by Pt-4(+) is less favored thermodynamically than Ptn+ (n = 1, 2, 3). On the basis of theoretical analyses, the differences in reactivity among the clusters and the nature of cooperative effect of the bimetallic cluster have been discussed. The calculated results provide a reasonable basis for understanding of experimental observations.