Lattice Mn Doping Enables Dual-Pathway CO2 Methanation on Ru/Cr2O3

Abstract

Rational design of highly active catalysts for low-temperature CO2 methanation remains a critical challenge for efficient CO2 utilization. Herein, we demonstrate that Mn incorporation into the Cr2O3 lattice, rather than surface modification, markedly enhances the catalytic performance of Ru/Cr2O3 catalysts. The optimal Ru/Mn0.10Cr0.90Ox catalyst (2.24 wt % Ru) achieves 91% CO2 conversion at 200 °C with a space velocity of 36,000 mL gcat–1 h–1, substantially exceeding that of the parent Ru/Cr2O3 (4% at 200 °C). Compared with Ru/Cr2O3, Ru/Mn0.10Cr0.90Ox exhibits a 4.1-fold higher turnover frequency at 180 °C, confirming the intrinsic catalytic enhancement conferred by Mn lattice doping. Comprehensive characterization revealed that Mn lattice doping generates Mn-O-Cr bonds, creating distinct Ru/O-Cr-Ov-Mn interfacial sites in contrast to the Ru/O-Cr-Ov-Cr interfaces present in undoped Ru/Cr2O3. In situ DRIFTS and H2-TPSR-MS studies demonstrated that low-temperature CO2 methanation on Ru/Mn0.10Cr0.90Ox proceeds concurrently via both CO* and HCOO* intermediate pathways, whereas only the CO* pathway operates on Ru/Cr2O3. DFT calculations revealed that Mn doping selectively modulates CO2 adsorption at the interface while minimally affecting bridged Ru sites. At the Ru/O-Cr-Ov-Mn interface, oxygen vacancies form and regenerate more readily than at the Ru/O-Cr-Ov-Cr interface during CO2 methanation, enabling an additional HCOO* pathway. This dual-pathway mechanism fundamentally underpins the enhanced low-temperature activity of Ru/Mn0.10Cr0.90Ox and provides a promising design strategy for developing efficient CO2 methanation catalysts.