(461d) A Density Functional Theory Study on Bimetallic Transition-Metal-Doped CeO? Catalysts for the Reverse Water Gas Shift Reaction

Anthropogenic greenhouse gas emissions, especially carbon dioxide (CO₂), have significantly contributed to global warming. The reverse water-gas shift (RWGS) reaction, which transforms CO₂ and H₂ into CO and H₂O, offers a promising solution. A recent study revealed that single-metallic transition-metal-(TM)-doped-CeO₂ (M-CeO₂) catalysts (M=Fe, Co, Ni, and Cu) effectively improved surface reducibility and CO₂ adsorption in RWGS reaction, with Fe achieving the highest CO₂ conversion (>56% at 600 °C) and 100% selectivity towards CO. However, a considerable gap remains between the conversion of the best M-CeO₂ and that predicted from equilibrium.

To bridge this gap, this study conducted a theoretical investigation using density functional theory (DFT) calculations on bimetallic TM-doped-CeO₂ (M₁M₂-CeO₂) catalysts (M₁=Fe; M₂=Co, Ni, Mn, and Cu) to further optimize CeO₂’s surface structure for the RWGS reaction. Oxygen vacancy (OV) was considered to improve CO₂ reduction efficiency. To the authors’ knowledge, this theoretical study is the first to consider bimetallic TM-doped-CeO₂ for the RWGS reaction. The investigation focused on the direct reduction of CO₂ to CO on catalyst surfaces by employing a four-step DFT calculation process: (1) bimetallic-doping to pure CeO₂ (111) surface, (2) OV creation, (3) CO₂ adsorption, and (4) CO₂ dissociation.

Given the time-consuming nature of transition state calculations and observed linear Brønsted-Evans-Polanyi relationships, reaction energy was used as a catalyst performance descriptor. Results (Figure 1) indicate that bimetallic M₁M₂-CeO₂ catalysts outperformed single-metallic TM-doped-CeO2 catalysts reported in the literature, exhibiting significantly lower reaction and CO₂ dissociative adsorption energies, thus reducing energy barriers and enhancing efficiency and feasibility for the RWGS reaction. Moreover, two bimetallic catalysts achieved negative CO₂ dissociative adsorption energies, making Step (4) spontaneous and potentially enhancing cost-efficiency for industrial-scale applications by eliminating heating requirements for that step. Overall, these results highlight the promising potential of bimetallic TM-doped-CeO₂ catalysts in enhancing catalytic performance for the RWGS reaction.