Reaction kinetics of liquid organic hydrogen carriers from first-principles: The methylcyclohexane/toluene pair on Pt(111)

The use of hydrogen as an energy carrier relies on efficient storage technologies. One appealing alternative is Liquid Organic Hydrogen Carriers (LOHC) where hydrogen is stored in liquid organic molecules at standard conditions. Catalysts are used to facilitate the loading and unloading of hydrogen in the organic molecule and one example is the storage of three hydrogen molecules in toluene (C 7 H 8 ) forming methylcyclohexane (C 7 H 14 ). We have used Density Functional Theory (DFT) calculations in combination with mean-field microkinetic modeling to understand the factors controlling the activity and selectivity of Pt(111) as catalyst for the toluene/methylcyclohexane LOHC pair. The simulated temperature dependence of turnover frequencies, reaction orders, and apparent activation energies are in agreement with experimental trends and the rate controlling steps are identified. The simulations reveal that stabilization of methylcyclohexane adsorption is one potential way to improve the rate of dehydrogenation. The unwanted side reaction of hydrodemethylation of toluene to benzene is not relevant on Pt(111), however, the simulations indicate that the presence undercoordinated Pt-sites will make this pathway an issue.