Mn-Promoted Surface Modification of MgO in Cu-Based Catalysts Enhances the Low-Temperature Reverse Water-Gas Shift Reaction

Abstract

Effective catalysts for converting carbon dioxide into value-added chemicals highly contribute to achieving net-zero emissions. The reverse water-gas shift (rWGS) reaction is essential for CO2-to-CO conversion, yet its efficiency at low temperatures remains limited. Herein, we demonstrate that Mn-doped Cu/MgO catalysts (MgCuXMnY) deliver high rWGS activity at a low temperature. The optimized catalyst (MgCu45Mn5) exhibited rWGS activity of 410.6 mu mol(CO2) g(cat)(-1) s(-1) at 400 degrees C with >99% CO selectivity. Comprehensive experimental and computational analyses revealed the distinct yet cooperative roles of Cu, MgO, and Mn: Cu serving as the active center for H-2 dissociation into H atoms (H+/e(-) pairs), MgO acting as a basic support that hosts surface Mg-OH groups and stabilizes key reaction intermediates along the associative pathway, and Mn functioning as an electronic promoter that enhances the reactivity of oxygen species at the Cu/MgO interface. Specifically, Mn doping into MgO altered lattice parameters and drove Mn valence cycling (Mn2+ <-> Mn3+ <-> Mn4+) via Mn <- O electron transfer (charge compensation), promoting electrophilic oxygen species (O-2(-), O-) formation and accelerating Mg-OH formation. These surface Mg-OH groups intensified the adsorption of CO2 through hydrogen bonding (O-H & centerdot;& centerdot;& centerdot;O-CO2), activating into reaction intermediates. Further, Mn-driven electron back-donation facilitated CO formation, exhibited by effectively weakened C-O and C-H bonds in the reaction intermediates. Ab initio calculations revealed that Mn doping upshifts band gap states, increasing charge transfer and boosting the level of CO2 and H adsorption. Comparative CO2 adsorption studies onto -OH groups indicated stronger CO2 adsorption for the Cu/MgO-Mn system, further validating the boosted CO2 adsorption by Mn-induced hydrogen bonding. This work establishes the optimization of Mn-promoted MgO as an effective strategy for Cu-based catalyst support engineering, providing a blueprint for efficient, low-temperature CO2 conversion.