Effects of sulfur on dehydrogenation of methylcyclohexane over platinum catalysts

Abstract

Liquid organic hydrogen carriers (LOHCs) enable storage and transport of H₂ using existing liquid fuel infrastructure, through reversible catalytic hydrogenation and dehydrogenation of organic molecules. A viable, commercially deployed, LOHC system is the methylcylohexane (C₇H₁₄)/toluene (C₇H₈) system. However, the Pt-based catalysts, which are used for both hydrogenation of C₇H₈ and dehydrogenation of C₇H₁₄, also promote unwanted C-C bond scission, leading to demethylation and LOHC degradation. One route to prevent C-C bond scission over Pt catalysts is to mildly poison the catalyst with sulfur. Using density functional theory (DFT) calculations and mean-field kinetic modeling, we show that the presence of sulfur, besides suppressing demethylation, also improves the C₇H₁₄ dehydrogenation activity. The enhanced performance is a result of sulfur destabilizing neighboring co-adsorbates, which promotes C₇H₈ desorption. Our computational results for dehydrogenation over Pt surfaces reproduce experimental trends for alumina-supported Pt nanoparticles, suggesting that controlled, moderate sulfur poisoning is a universal means to improve the overall performance of Pt catalysts for LOHC dehydrogenation.