Probing the Catalytic Roles of Surface Hydroxyls on Ir/Al2O3 in Dissociation and Dry Reforming of Methane

The synergistic catalysis between the active metal site and the oxide support is crucial for catalytic dry reforming of methane (DRM); however, the specific roles of hydroxyl groups at the metal–oxide interface have been particularly elusive. To probe this, Ir/Al2O3 model catalysts (Ir/Al2O3-400R and Ir/Al2O3-650R reduced at 400 and 650 °C, respectively) were constructed with isolated Ir sites but distinct hydroxyl properties. Both catalysts exhibited high activity and coke-resistant stability in long-term DRM reactions at 650 °C. By a combination of structure characterizations, kinetic analyses, and in situ isotopic spectral techniques, their catalytic performances are correlated with the hydroxyl structures. The surface hydroxyls are directly involved in CH4 and CO2 dissociation pathways, and specifically, the triply bridged hydroxyl (μ3-OH), a strong proton donor, cooperates with the Ir metal site to achieve decoupled CH4 dissociation. Beyond this synergistic effect, a complete cycle of hydroxyl conversion and regeneration is integral to the DRM mechanism. These findings offer a mechanistic perspective on the catalytic roles of hydroxyls in CH4 dissociation and dry reforming.