Mechanism-Guided Catalyst Design for CO2 Hydrogenation to Formate and Methanol

Conspectus CO2 to formate/formicacid and methanol has emergedas a promising method for utilizing CO2 in chemical andfuel synthesis, as well as reducing CO2 emissions whenH(2) is produced through renewable energy sources. This reactionrequires the activation of two chemically distinct molecules, CO2 and H-2, along with the selective formation ofthe desired product. Creating efficient catalysts that surpass thelimitations of existing catalysts remains a significant challenge.Historically, the development of catalysts has largely depended ontrial and error until successful outcomes are achieved. However, recentadvances in material synthesis for well-defined structures, reactionkinetics analysis, in situ characterization techniques, and computationalstudies have facilitated a systematic understanding of catalytic reactionsand enabled mechanism-guided catalyst development. This innovativeapproach has empowered researchers to strategically design effectivecatalysts that optimize the target reaction, particularly the rate-determiningstep, while tackling other limitations, such as selectivity and stability. This Account provides an overview of our recentefforts in catalyst development for CO2 hydrogenation throughmechanism-guided engineering, which are primarily divided into twosections: (i) formic acid/formate and (ii) methanol production. Forthe CO2 hydrogenation to formate/formic acid, we firstdiscuss the structure-activity correlation studies of variousmetal/support catalyst systems, including different metal particlesizes, types of support, and crystalline morphologies of the support.These studies highlight the crucial role of electron-rich metal sitesfor H-2 splitting and an adequate number of weak basic sitesfor CO2 activation, which inform the design of improvedcatalysts with unique architectures. Notably, encapsulated metal clustercatalysts enhance the utilization of metal species and optimize thesynergistic interaction between metal active sites and the supportmaterial. The encapsulation strategy can also be applied to inexpensivemetal elements such as Ni, facilitating the development of highlyefficient catalysts. Our primary focus for CO2-to-methanolcatalysts is thedesign of active and durable oxide-based catalysts. We first identifythat the critical limitation of metal oxide catalysts is their poorH(2) activation capability, based on a comprehensive reviewof classical and state-of-the-art understanding of the CO2-to-methanol catalysts. Consequently, the principal catalyst designconcept involves coupling metal promoters, which provide high H-2 activation functionality, with metal oxide catalysts thatenable the adsorption of CO2 and selective methanol synthesis.An essential synthetic approach is the doping of metal promoters onthe surface of oxide catalysts. Specifically, atomically dispersedmetal promoters significantly improve methanol yield by maximizinginterfacial synergy with the oxide catalyst. A remarkable strategyis the incorporation of a hydrogen dispenser, such as conductive carbon,between the metal promoter and the oxide catalyst. This multicomponentcomposite dramatically enhances hydrogen delivery from metal sitesto active sites via long-range hydrogen spillover, resulting in acceleratedmethanol synthesis. The approach overcomes the limitation of conventionalmetal/oxide systems, which constrain hydrogen movement across thesurface of the oxide catalyst. We conclude by discussing the underlyingimplications of these observations and offering perspectives on futureresearch and development opportunities.