Review on sequential catalysis for higher alcohols: overcoming barriers in direct CO2 hydrogenation

Abstract

In recent years, the escalation of global warming driven largely by rising carbon dioxide (CO₂) emissions has intensified the urgency to develop innovative solutions for reducing greenhouse gases. One promising avenue is the transformation of CO₂ into higher alcohols, which not only offers a pathway to valuable chemical products but also utilizes CO₂ as a renewable carbon source. The procedure of directly hydrogenating CO₂ to create higher alcohols has received a lot of interest, but it is fundamentally complicated. It involves multiple reaction steps and requires multifunctional catalysts with well-orchestrated active sites to drive the various transformations efficiently. Achieving precise nanoscale control over these catalytic interfaces remains a significant barrier to advancing this direct route. An alternate approach to overcoming these constraints is the adoption of sequential catalytic reactions, including olefin hydration, syngas conversion, CO₂-based Fischer–Tropsch synthesis, methanol formation, and the reverse WGS reaction. Instead of depending on a single-step transformation, this tandem strategy couples separate, proven processes to enable the inverse process of turning CO₂ into higher alcohols. This review critically explores these indirect routes for synthesizing higher alcohols from CO₂. It begins by evaluating the thermodynamic constraints and selectivity challenges associated with direct CO₂ hydrogenation. The discussion then shifts to the concept of physically integrating multiple catalysts to create systems with complementary functionalities. Various conversion pathways are outlined, alongside advanced catalysts designed for each specific step. In conclusion, the strengths and drawbacks of these methodologies are compared, highlighting the considerable promise of tandem reaction networks as a viable and efficient route for upgrading CO₂ into higher alcohols.