Relativistic DFT studies of dehydrogenation of methane by Pt cationic clusters: Cooperative effect of bimetallic clusters

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 CR₄, cleavage of the first C-H bond is quite facile without barrier. The second C-H bond activation and the release of H₂ from molecular complex are generally the rate-determining steps. In the reactions of platinum clusters Pt _n⁺ (n = 2-4) with CH₄, the H₂ elimination from the dihydrogen complex is the rate-determining step. Spin crossover may occur in the reaction of Pt²⁺ and CH₄. Pt₂⁺ and Pt₃⁺ can dehydrogenate methane efficiently due to remarkable thermodynamic stability of the products. The dehydrogenation of methane induced by Pt₄⁺ is less favored thermodynamically than Pt_n⁺ (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.