Research progress on mechanism and catalysts for reverse water-gas shift reaction

CO₂ emissions rapidly growth have lead to the deterioration of the global environment, which seriously endangers the human living environment, effective measures must be taken to curb the continuous growth of CO₂ emissions. Reverse water-gas shift (RWGS) reaction is an effective way to reduce carbon emission and realize carbon resource utilization. CO₂ can be converted into CO via reverse water-gas shift reaction, followed by Fischer-Tropsch reaction to produce olefin chemicals and alcohol fuels, which have a great significance for improving the environment and changing the future energy structure. In this review, the RWGS reaction mechanisms were summarized firstly, maining introducing the research progress of RWGS reaction mechanism latest findings in recent years, according to whether H₂ is directly involved in the reduction reaction in the path of CO₂ converted into CO, the redox mechanism and associative mechanism are divided, the associative mechanism including formate, carboxylate and carbonate pathways. The RWGS reaction mechanisms are highly dependent on catalyst properties, different metal active sites and carriers can provide different mechanisms for RWGS, such as controlling the metal particle size can change CO₂ hydrogenation pathway and optimize product selectivity, the increase of catalyst surface alkalinity can promote the transition from redox mechanism to association mechanism, and the reaction mechanism of carbon vacancy and sulfur vacancy as active sites, etc. Then, the research progress of catalysts for thermocatalytic conversion via CO₂ with H₂ co-feeding and chemical looping in RWGS were reviewed. The RWGS reaction performance of metal-based catalysts such as Pt, Ni, Cu, ect and metal carbide and phosphide materials were discussed, as well as the application of perovskite oxygen storage materials (OSM) in chemical looping reaction. At present, the research of RWGS catalysts mainly focuses on the improvement of catalytic performance, the activity, selectivity and stability of catalysts can be optimized by controlling the metal particle size and optimizing dispersibility, adding modifiers or alkaline accelerators, producing synergistic effects through metal alloying, increasing the oxygen vacancy on the carrier and improving the preparation method, etc. As the donor and acceptor of oxygen vacancy in RWGS-CL reaction, perovskite OSM avoid thermodynamic and kinetic constraints and eliminates the possibility of CO₂ methanation as a side reaction. Finally, the key research directions in reaction mechanism and catalyst of RWGS reaction are further anticipated. Based on the difference and diversity of RWGS reaction mechanism, the optimal pathway of RWGS reaction on different catalysts, the formation and transformation of key reaction intermediates, and the relationship between active sites and key reaction intermediates should be studied by combining various simulation calculation and characterization methods in the future, so as to provide theoretical guidance for catalyst design. The catalyst of RWGS have not yet been commercially applied, so catalysts with high efficiency and stable performance are still the focus of RWGS reaction research in the future. And, the development of new technologies addressing the shortcomings of thermocatalytic pathway is also very important, such as insitu dewatering can be achieved through membranes, which reducing the thermodynamic equilibrium restriction. This review aims to provide some references for the subsequent research of RWGS catalytic materials.