Hydrogen‐Assisted Ring Opening of Methylcyclohexane on Pt(111) and Ir(111): A Comparative Theoretical Study of the Reaction Mechanism

Ring‐opening reactions over noble‐metal catalysts show a strong dependence on the metal, but the mechanistic origin of the different behavior remains poorly understood. In this theoretical study, we investigated the hydrogen‐assisted hydrogenolysis mechanism for the ring‐opening of methylcyclohexane, together with the associated product selectivity, by analyzing the relevant mechanistic pathways on iridium (Ir) and platinum (Pt) surfaces, which are commonly used catalysts for hydrocarbon hydrogenolysis. The calculated activation barriers reveal that Ir(111) consistently exhibits lower C─C cleavage barriers than Pt(111) across all pathways, in agreement with experimental observations. To elucidate the origin of this difference, we analyzed the catalytic activity on Ir(111) and compared it with Pt(111). The results demonstrate that surface‐bound hydrogen plays a decisive role in facilitating the C─C hydrogenolysis step. Moderate hydrogen binding on Ir(111) enables efficient hydrogen transfer along the reaction pathway, whereas stronger hydrogen binding on Pt(111) restricts hydrogen mobility and reduces its participation in C─C cleavage. Overall, this comparative study provides valuable insights into the superior ring‐opening performance of iridium catalysts and highlights the critical role of surface hydrogen energetics in determining catalytic activity.