Entropy-Enhanced Catalysis Accelerates Low-Temperature CO2 Methanation via Intermediate Delocalization at Under-Coordinated Ru2+− V O Sites

Abstract In heterogeneous catalysis, the electronic structures of catalysts' active sites are modified to optimize intermediate binding and bond activation for achieving high reaction activity. However, studies on regulating the atomic structures of catalytic materials to enhance the configurational diversity of adsorbed intermediates remain scarce. Herein, we demonstrate that engineering under-coordinated active site motifs enables an entropy-enhanced catalytic mechanism that harnesses the configurational freedom of surface intermediates to improve reaction rates at reduced temperatures. Using CO2 methanation as a model reaction, we identified that under-coordinated Ru2+−oxygen vacancy (Ru2+−VO) sites promote delocalized catalyst−intermediate interactions and reduce the reaction energy barrier. Stable Ru2+−VO sites were created on Au nanoparticle-grafted (RuOx)a(CeOy)b solid-solution nanorods through plasmonic effects under reducing conditions. Eyring plot analysis revealed an activation entropy gain of TΔΔS‡ ≈ 12 kJ mol−1 for CO2 methanation at 300 °C, in situ spectroscopy revealed a *HCOO-mediated pathway, and ab initio molecular dynamics simulations indicated a 0.22 eV free-energy barrier for *HCOO formation on Ru2+−VO motifs. A CH4 production rate of 550 mmol gcat−1 h−1 with >98% selectivity and >280 h stability at 300 °C was achieved at a high gas hourly space velocity of 40,000−100,000 mL gcat−1 h−1. The findings provide a conceptual framework beyond adsorption energy optimization in catalyst design, showing that configurational entropy is a tunable descriptor for enhancing catalytic kinetics.