Heterogeneous processes, such as oxidative coupling of methane (OCM) and oxidative dehydrogenation (ODH) of alkanes, use metal oxides as catalysts, and the rate limiting steps are believed to involve the abstraction of hydrogen atom from alkanes by active oxygen species. The active oxygen species involved could be an oxyradical, a peroxyradical or a metal oxo. Figure 1 Possible active oxygen species on a metal oxide catalystFor small molecule chemistry, H abstraction is a typical property of radicals, which have at least one unpaired electron. For H abstraction by a metal oxo group, however, the mechanism is not yet well-established.We presented here a systematic theoretical study to explore the underlying mechanisms of the H abstraction from methane by various model abstracting agents (oxyradicals (RO�), peroxyradicals (ROO�) and high valence metal oxo complexes (MOxCl4-x)). We found that RO�, ROO� and M=O follow different Polanyi relations, showing that there are different factors that influence the mechanisms of the hydrogen abstraction processes. Our calculations reveal that a closed-shell metal oxo can enter into radical reactions by opening its M-O p bond and the activity of a metal oxo can be tuned by the M-O p bonding interaction. This finding is of importance in the design of an effective catalyst for the oxidative activation of a C-H bond.This work was supported by NSFC (21133004), and the Ministry of Science and Technology (2013CB834606, 2011CB808505).

Mechanisms for the selective oxidation of low alkanes by metal oxoes

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.