Because n‐butanol as a fuel additive has more advantageous physicochemical properties than those of ethanol, ethanol valorization to n‐butanol through homo‐ or heterogeneous catalysis has received much attention in recent decades in both scientific and industrial fields. Recent progress in catalyst development for upgrading ethanol to n‐butanol, which involves homogeneous catalysts, such as iridium and ruthenium complexes, and heterogeneous catalysts, including metal oxides, hydroxyapatite (HAP), and, in particular, supported metal catalysts, is reviewed herein. The structure–activity relationships of catalysts and underlying reaction mechanisms are critically examined, and future research directions on the design and improvement of catalysts are also proposed.

catalyst exhibited 49.8% of ethanol conversion, 48.6% of selectivity toward n-butanol, and thereby 24.2% of n-butanol yield at relatively low temperature (523 K) and pressure (2 MPa) during a 200 h long-term evaluation. The high catalytic activity and selectivity of Pd@UiO-66 catalyst are primarily ascribed to the close synergy of highly dispersed Pd nanoparticles and coordinatively unsaturated Zr sites on Zr 6 nodes of UiO-66, as active centers for dehydrogenation/hydrogenation and aldol condensation, respectively; however, the high stability of the catalyst is mainly attributed to the electrostatic attraction of Pd nanoparticles with Zr 6 nodes and the confinement effect of the cavities of UiO-66.

Aldol condensation is a very useful reaction for biomass upgrading by coupling small molecule platform compounds into high value-added products. Here we choose acetaldehyde (AcH) condensation, the rate-determining step in bioethanol transformations, as a targeted reaction, and prepared four CeO 2 catalysts with different concentrations of surface oxygen vacancies to investigate the role of oxygen vacancies in this reaction. To the best of our knowledge, it is the first time to demonstrate that there is a linear correlation between the activity of aldol condensation and the concentration of oxygen vacancies. Based on in-situ FTIR studies, we conclude that oxygen vacancies are the Lewis acid sites for activation and stabilization of AcH, while lattice oxygen act as base sites for the formation of enolate species which are the key intermediates for AcH coupling reactions. Moreover, the proposed reaction mechanism indicates that Ce cations which are weak Lewis acid sites are not involved in the AcH condensation.

Cu‐based catalysts have been widely used in ethanol upgrading to value‐added chemicals, however the selectivity towards target products is still not satisfactory due to the complexity of reaction network. Herein, we take the ethanol conversion to n‐butanol as an example, and demonstrate that there are relationships of the ethanol conversion, the selectivity of n‐butanol and ethyl acetate, and the rate of n‐butanol formation with the ratios of the surface area of Cu0 and Cu+. Both Cu0 and Cu+ are involved in the formation of ethyl acetate, and the ratio is indicative of the catalytic performance, being the higher the ratio, the higher activity of ethanol conversion to n‐butanol but lower selectivity towards ethyl acetate. This work will help develop more efficient and selective catalysts for ethanol upgrading.

The Ethanol‐to‐Butadiene (ETB) process is experiencing a renaissance with the increasing shortage of petroleum‐based resources, however, the development of active catalysts for this process still remains sluggish due to the lack of fundamental understanding of the properties of catalysts, especially acidity and basicity. We present here that individual reaction step in the ETB process requires specific acid or/and basic sites with different strengths and densities. Weak acid and moderate basic sites are beneficial for ethanol dehydrogenation, while moderate basic sites with optimal strength are also active for condensation and Meerwein‐Ponndorf‐Verley‐Oppenauer (MPVO) reactions. In contrast, moderate and strong acid sites cause the ethanol dehydration, lowering the selectivity towards 1,3‐butadiene (BD) production. Moreover, the selectivity and yield of BD are more dependent on the properties of sites for both condensation and MPVO reactions than for dehydrogenation reaction.