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

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.