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 methylcyclohexane (C₇H₁₄)/toluene (C₇H₈) system. However, 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 microkinetic 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. The 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.