Reaction mechanism and structure-activity relationships of bimetallic catalysts for CO2 hydrogenation to methanol under vapor and liquid phase processes

Under the global context of carbon capture, utilization and storage (CCUS), coupling CO 2 with green hydrogen to synthesize green methanol at low temperature has become the development trend of this field. In gas and liquid phase systems, CO 2 hydrogenation demands different intermediates, directly determining the rate determining step and deactivation mechanism, thus requiring different catalyst design. Bimetallic catalysts have become the most promising research topic due to their excellent catalytic performance and stability. Although numerous reviews on CO 2 hydrogenation to methanol exist, most primarily focus on the activity and selectivity of bimetallic catalysts under gas-phase reaction conditions. While certain factors influencing catalytic performance and reaction mechanisms have been addressed, a systematic comparison of bimetallic catalysts from the perspective of gas versus liquid phase hydrogenation, highlighting their similarities and differences during the reaction process, remains rare in the literature. Therefore, after systematically comparing gas and liquid phase hydrogenation processes, this review expounds the reaction mechanism of bimetallic catalysts in gas and liquid phase systems. By comparing intrinsic metal pairs and different supports, analyzing the structure activity relationships in electronic modulation, geometric regulation, and coupling of dual functional mechanisms. Finally, the shortcomings and challenges of bimetallic catalysts such as balancing CO 2 conversion, methanol selectivity, improving catalytic activity and stability, activating in active key intermediates are highlighted. Furthermore, the reaction pathways and key challenges of amine-captured CO 2 hydrogenation to methanol were systematically reviewed and prospected, offering a comprehensive reference framework for the development of low-energy integrated processes and the next generation low temperature CO 2 hydrogenation to methanol catalysts. • Systematic comparison of CO 2 hydrogenation: gas-phase vs. liquid-phase routes. • Low-temperature liquid-phase hydrogenation as most promising pathway. • Catalyst design must shift to a process-oriented paradigm. • Process-driven design principles: charge transfer, geometry control, synergy.