CO2 capture in the presence of O2 and selective hydrogenation to CO over an Ag–K dual functional material (DFM): comparative investigation with a Cu-based DFM

Abstract

The CO₂ capture and reduction (CCR) over dual-functional materials (DFMs) is promising as an alternative utilization strategy of low-concentration CO₂ in exhaust gases and/or air. Despite much effort toward the development of DFMs for CH₄ formation through CCR, the study of DFMs for CO formation has been less reported. In particular, DFMs workable under milder reaction temperature and O₂ co-existing conditions have been rarely developed. In this work, Ag-based DFMs were investigated for CO₂ capture in the presence of O₂ and selective hydrogenation to CO. Ag and K co-loaded Al₂O₃ exhibited the best CO formation performance among different alkaline (earth) metal co-loaded materials. The O₂ compatibility of Ag–K/Al₂O₃ was also studied by comparing with Cu–K/Al₂O₃. The reduced Cu species were oxidized by O₂ into Cu oxides, and thus the reduction of Cu species after gas switching to H₂ occurred. In contrast, the reduced Ag state was maintained even after CO₂ capture in the presence of O₂ over Ag–K/Al₂O₃, which results in the suppression of water formation after gas switching to H₂ and consecutive desorption of captured CO₂. The distinct O₂ compatibility is ascribed to the different redox properties between Cu–K/Al₂O₃ and Ag–K/Al₂O₃.