State-of-the-Art advancements in the thermocatalytic conversion of CO2 into ethanol and higher alcohols: Recent progress in catalyst development and reaction mechanisms

The production of ethanol and higher alcohols (HA) via CO2 hydrogenation with achieving high product selectivity and catalyst stability is a difficult scientific and technological challenge due to chemical inertness of CO2, complexity in various reaction routes, and uncontrollability of C–C coupling from untamed surface moieties in HA synthesis. One of the main solutions is a catalyst design, which can overcome these issues. Hence, in this review, we summarize and analyze the recent advances in thermocatalytic direct CO2 hydrogenation into ethanol and HA in batch and continuous fixed-bed reactors. The introductory section delves into the discourse surrounding carbon capture and utilization, highlighting the constraints imposed by reaction thermodynamics, and emphasizing the indispensable role of catalysts in the conversion of CO2 to ethanol and HA. The second section highlights the potential promising catalyst families, in a batch reactor, including modified Cu-based catalysts, modified Co-based catalysts, and a noble-metal catalysts, together with various promoters, supports, and solvent effects specified in each case. The third section reviews the family most active catalysts, but in continuous fixed-bed reactor, including modified Cu-, Co–, Fe-based and noble metals catalysts. The fourth section reviews the possible reaction mechanisms (CO-mediated pathway, formate/methoxy-mediated pathway, and C–C coupling pathways) for ethanol and HA production. Ultimately, the conclusion and future perspectives are provided to offer a forward-looking assessment of catalyst development including approaches to enhance selectivity towards ethanol/HA based on the available experimental results.