Computational Study of Methane Activation on γ-Al2O3.

Abstract

The C–H activation of methane remains a longstanding challenge in the chemical industry. Metal oxides are attractive catalysts for the C–H activation of methane due to their surface Lewis acid–base properties. In this work, we applied density functional theory calculations to investigate the C–H activation mechanism of methane on various sites of low-index facets of γ-Al2O3. The feasibility of C–H activation on different metal–oxygen (acid–base) site pairs was assessed through two potential mechanisms, namely, the radical and polar. The effect of surface hydroxylation on C–H activation was also investigated to examine the activity of γ-Al2O3 under realistic catalytic surface conditions (hydration). On the basis of our calculations, it was demonstrated that the C–H activation barriers for polar pathways are significantly lower than those of the radical pathways on γ-Al2O3. We showed that the electronic structure (s- and p-band center) for unoccupied and occupied bands can be used to probe site-dependent Lewis acidity and basicity and the associated catalytic behavior. We identified the dissociated H2 binding and final state energy as C–H activation energy descriptors for the preferred polar pathway. Finally, we developed structure–activity relationships for the C–H activation of methane on γ-Al2O3 that account for surface Lewis acid–base properties and can be utilized to accelerate the discovery of catalysts for methane (and shale gas) upgrade.