Tandem catalysis for CO2 conversion to higher alcohols: A review

In recent years, due to the substantial emission of CO2, global warming has become more severe, and there is an urgent need to develop technologies to reduce greenhouse gas CO2 emissions. Converting CO2 into higher alcohols is a promising process, as it not only produces valuable chemicals but also utilizes CO2 as feedstock. Currently, most reported catalytic approaches are based on direct hydrogenation of CO2 to synthesize higher alcohols. However, the synthesis of higher alcohols involves multiple steps, requiring catalysts with multiple functional sites and their synergistic interactions are crucial. Nevertheless, controlling catalysts at the nanoscale poses challenges, hindering the design of efficient multi-site catalysts. An alternative approach worth considering is to perform a tandem of multiple well-established catalytic reactions (e.g., methanol synthesis, CO2-Fischer-Tropsch-Synthesis, RWGS, syngas conversion, olefin hydration, etc.) to indirectly achieve the conversion of CO2 into higher alcohols, instead of direct CO2 hydrogenation. Therefore, in this review, these alternative strategies of higher alcohols synthesis are discussed, and their potential is evaluated. First, thermodynamic analysis, the selective adjustment strategies, and the current challenges faced for direct CO2 hydrogenation are introduced. Then, physical integration of multiple catalysts as a feasible strategy to endow the catalyst with multifunctional properties is discussed. Subsequently, several feasible routes of CO2 conversion into higher alcohols and the advanced catalysts employed for each pathway are summarized. Finally, merits and limitations of the different approaches are provided, emphasizing the great potential the tandem reaction strategy holds for the efficient synthesis of higher alcohols by CO2 conversion.