Transition metal oxo sites in zeolites show high activity for the conversion of methane to methanol. Despite remaining challenges encouraging results have been obtained for these systems in recent years. Similar active centers are known in homogeneous catalysis. However, in zeolites also the framework will interact with the reactants and confinement effects will have a major influence on the reaction. They are based on van der Waals interactions, which still pose major problems in a theoretical description.<br/><br/>In this work we model the conversion of methane to methanol over Fe-oxo sites in the zeolite SSZ-13 using the dispersion-corrected PBE-d density functional and RPA, a method that accurately models van der Waals interactions. The reaction itself proceeds via a rebound mechanism, where first a hydrogen atom is abstracted from the methane molecule and afterwards methanol is formed in the so-called rebound step. The reaction is highly exothermic and barriers are relatively low. However, the methyl intermediate shows a high stabilization using RPA. We attribute this change to a change in the polarizability within the reactant. This does not only lead to a strong stabilization of the intermediate, but also to earlier transition states and clear energetic differences between different reaction paths.<br/><br/>The work presented here illustrates how confinement affects the conversion of hydrocarbons in zeolite catalysts. At the same time it allows a deeper understanding of descriptor-based approaches for confinement effects and leads to clear guidelines for the choice of zeolite framework for methane to methanol conversions in zeolites.

Insights in confinement effects in methane-to-methanol conversion over Fe-SSZ-13

249th National Meeting (2015)

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