Unveiling the Role of Hydroxyls on Catalyst Surface in CO₂ Hydrogenation Reaction

Understanding and tailoring catalyst surface species is crucial for controlling reaction pathways and product selectivity. Herein, we demonstrate that triply bridging hydroxyl (tOH) on ceria oxide surfaces profoundly alter the CO₂ hydrogenation pathway, shifting the major product from CO to CH₄. Steam treatment of CeO₂ supported rhenium catalyst generates abundant t-OH species, leading to a tenfold increase in the CH₄ formation rate and ∼90% selectivity at 340°C and 30 bar. The operando spectroscopy combined with isotope-labeling experiments provide direct evidences for the involvement of t-OH in CH₄ formation. Density functional theory calculations reveal that t-OH acts as a reactive proton donor, facilitating the hydrogenation of ^*HCOO to ^*HCOOH and thereby suppressing the decomposition of ^*HCOO to CO. Kinetic analysis further indicates that the presence of t-OH lowers the apparent activation energy from 118.8 kJ mol^-1 to 73.2 kJ mol^-1, enabling a more efficient methanation pathway. This phenomenon is also discovered to be universal on other oxide-supported Ni, Ru, and Rh catalysts. This work highlights the pivotal role of surface hydroxyls in CO₂ hydrogenation reaction and offers fundamental insights into engineering surface-species to modulate product selectivity.