(768f) Screening of Active Site Motifs for C-H Bond Activation in Nanoporous Catalysts

Given the availability of new natural gas resources, direct transformation of methane to higher value commodity chemicals or liquids fuels is likely to revolutionize the energy and chemicals industry. However, the high economic barriers associated with methane activation have hindered the development of such technologies. Many materials including zeolites, metal organic frameworks, graphenes, metal surfaces, oxides, porous organic polymers and nanoparticles have been shown to be feasible for C-H bond activation, but a unified understanding of the activation process is not available. Although the material properties, reactants and proposed active sites for the above systems are very different, we show that a unifying feature is the radical-like geometry of the transition state (TS) during reaction. In this work, we discuss a universal model for predicting C-H activation barriers, where the TS energy scales linearly with the hydrogen affinity energy. Furthermore, by combining this scaling approach with a thermodynamic analysis for the number of active sites, we illustrate a catalyst screening strategy using a simple descriptor for various classes of materials. This analysis identifies a subset of candidate zeolites and porous organic polymers that are likely to be active and selective for partial methane oxidation. Although we focus on the methane oxidation reaction in this work, our active site motif approach is likely to be transferable to other reactions and will be of a broader interest to nanoporous and surface catalysis community.