Theoretical insight into the C–H and C–C scission mechanism of ethane on a tetrahedral Pt4 subnanocluster

Abstract

The activation mechanism of C₂H₆ on a Pt₄ cluster has been theoretically investigated in the ground state and the first excited state potential energy surfaces at the BPW91/Lanl2tz, aug-cc-pvtz//BPW91/Lanl2tz, 6-311++G(d, p) level. On the Pt₄ cluster, the optimal channel order was kinetically as follows: demethanation > dehydrogenation > deethylenation from C₂H₆. The two-fold dehydrogenation of ethane to acetylene was almost equivalent to its single dehydrogenation to ethylene, both thermodynamically and kinetically. In addition, the C–H cleavage intermediate was kinetically more preferable than the C–C cleavage intermediate, while both the C–H cleavage intermediate and the C–C cleavage intermediate were thermodynamically favoured. Nevertheless, the extremely stable C–H cleavage intermediate was trapped in a deep well, which hindered the release of H₂. Together with the excellent reactivity of the Pt₄ cluster, for the design of an efficient and selective catalyst towards the dehydrogenation of C₂H₆, one can expect that it is necessary to improve the release of H₂ from the C–H cleavage intermediate by introducing some additive or support into the Pt₄ cluster, which decreases the binding of the catalyst towards H₂. Concerning selectivity, the Pt atom was the most favourable for the dehydrogenation, the Pt₂ cluster was the most preferable for deethylenation, and the Pt₄ cluster was the most beneficial for the demethanation. Both Pt₄ and Pt₂ clusters exhibited more promising catalytic performance compared with the mononuclear Pt atom towards C₂H₆ activation.