Catalytic Upgrading of Ethanol to n‐Butanol: Progress in Catalyst Development

Abstract

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.

Catalytic Enhancement of Aldol Condensation by Oxygen Vacancy on CeO2 Catalysts

“…The product distribution (Table ) shows that crotonaldehyde is the dominant coupling product for all the CeO 2 catalysts and other by‐products account for the rest selectivity of no more than 12%. Other minor by‐products involve ethanol formed via a Cannizzaro disproportionation reaction with a concomitant formation of acetic acid, ethyl acetate generated either from a Tishchenko reaction of AcH or a esterification reaction of acetic acid with ethanol, and ether originated from the dehydration of ethanol . Furan and its derivative (2,5‐dimethylfuran) resulted from the ring closure of crotonaldehyde and 2,4‐hexadienal, respectively .…”

“…A variety of platform molecules have been identified, including ethanol, glycerol, lactic acid, furfural, levulinic acid, etc. Among others, ethanol, 90% of which is now derived from biomass, is a promising platform molecule for the production of a wide range of value‐added products, such as n‐butanol, isobutanol, butadiene, isobutene . All these ethanol transformations have a common reaction step, adol condensation of acetaldehyde (AcH) that originated from ethanol dehydrogenation.…”

Copper‐Basic Sites Synergic Effect on the Ethanol Dehydrogenation and Condensation Reactions

“…This fact suggests an undesired phenomenon that partially deactivates the material at these more severe conditions. One of the possible reasons of this behavior is the copper nanoparticle sintering (major drawback of copper regarding other metals).…”

Efficient conversion of ethanol to 1-butanol and C5–C9 alcohols over calcium carbide

“…In this route, the acid sites of heterogeneous catalysts adsorb ethanol and acetaldehyde, and the base sites catalyze the hydrogen transfer reaction. 16,19,22,34 A direct condensation mechanism shown in Scheme 2 has also been reported on various basic solids, 17,18,20 in which the b-H in ethanol is activated by a catalyst and the activated ethanol molecule subsequently condenses with another ethanol molecule through dehydration to form 1butanol. In both routes, activation of b-H is considered to be a crucial step.…”