Improving alkane dehydrogenation activity on γ-Al2O3 through Ga doping†
Nonoxidative alkane dehydrogenation is a promising route to produce olefins, commonly used as building blocks in the chemical industry. Metal oxides, including γ-Al2O3 and β-Ga2O3, are attractive dehydrogenation catalysts due to their surface Lewis acid–base properties. In this work, we use density functional theory (DFT) to investigate nonoxidative dehydrogenation of ethane, propane, and isobutane on the Ga-doped and undoped (100) γ-Al2O3 via the concerted and stepwise mechanisms. We revealed that doping (100) γ-Al2O3 with Ga atoms has significant improvement in the dehydrogenation activity by decreasing the C–H activation barriers of the kinetically favored concerted mechanism and increasing the overall dehydrogenation turnover frequencies. We identified the dissociated H2 binding energy as an activity descriptor for alkane dehydrogenation, accounting for the strength of the Lewis acidity and basicity of the active sites. We demonstrate linear correlations between the dissociated H2 binding energy and the activation barriers of the rate determining steps for both the concerted and stepwise mechanisms. We further found the carbenium ion stability to be a quantitative reactant-type descriptor, correlating with the C–H activation barriers of the different alkanes. Importantly, we developed an alkane dehydrogenation model that captures the effect of catalyst acid–base surface properties (through dissociated H2 binding energy) and reactant substitution (through carbenium ion stability). Additionally, we show that the dissociated H2 binding energy can be used to predict the overall dehydrogenation turnover frequencies. Taken together, our developed methodology facilitates the screening and discovery of alkane dehydrogenation catalysts and demonstrates doping as an effective route to enhance catalytic activity.