State-of-the-art advances in homogeneous molecular catalysis for the Guerbet upgrading of bio-ethanol to fuel-grade bio-butanol

The upgrading of ethanol to n-butanol marks a major breakthrough in the field of biofuel technology, offering the advantages of compatibility with existing infrastructure while simultaneously offering potential benefits in terms of transport efficiency and energy density. With its lower vapour pressure and reduced corrosiveness compared to ethanol, n-butanol is easier not only to manage but also to transport, eliminating the need for costly infrastructure changes. This leads to improved fuel efficiency and reduced fuel consumption. These features position n-butanol as a promising alternative to ethanol in the future of biodiesel. This review article delves into the cutting-edge advancements in upgrading ethanol to butanol, highlighting the critical importance of this transformation in enhancing the value and practical application of biofuels. While traditional methods for making butanol rely heavily on fossil fuels, those that employ ethanol as a starting material are dominated by heterogeneous catalysis, which is limited by the requirement of high temperatures and a lack of selectivity. Homogeneous catalysts have been pivotal in enhancing the efficiency and selectivity of this conversion, owing to their unique mode of operation at the molecular level. A comprehensive review of the various homogeneous catalytic processes employed in the transformation of feedstock-agnostic bio-ethanol to fuel-grade bio-n-butanol is provided here, with a major focus on the key advancements in catalyst design, reaction conditions and mechanisms that have significantly improved the efficiency and selectivity of these Guerbet reactions.