Surface structure effects on the methylcyclohexane dehydrogenation over Ni catalysts predicted by density functional theory

Dehydrogenation of methylcyclohexane (MCH) to toluene poses challenges in liquid organic hydrogen carrier (LOHC) systems. This study employs DFT-based microkinetic modeling to investigate the MCH dehydrogenation on Ni(111) and Ni(211) surfaces. At low conversion, methylcyclohexene is the primary product, with toluene only being produced on the Ni(211) surface (∼50% selectivity). At higher conversion, close to 100% selectivity to toluene is observed over both surfaces, highlighting the importance of methylcyclohexene re-adsorption and subsequent dehydrogenation. Ni(211) exhibits a rate approximately three orders of magnitude higher than Ni(111) but also suffers from stronger binding of toluene and coke precursors (C and CH), leading to site blocking and potential coke formation. Coke precursors are thermodynamically unstable on Ni(111). These insights suggest a dual strategy for optimizing Ni-based catalysts for LOHC applications: selectively poisoning undercoordinated edge sites to mitigate deactivation and enhancing the close-packed Ni(111) activity through doping or alloying.