Mechanistic Insights into the Selective Electroreduction of Crotonaldehyde to Crotyl Alcohol and 1-Butanol.

Abstract

The electroreduction of crotonaldehyde, which can be derived from the aldol condensation of acetaldehyde (sustainably produced from CO2 reduction or from biomass ethanol), is potentially a carbon-neutral route for generating high-value C4 chemicals such as crotyl alcohol and 1-butanol. Developing functional catalysts is necessary toward this end. Herein, the electrocatalytic conversion of crotonaldehyde to crotyl alcohol and 1-butanol was achieved in 0.1 m potassium phosphate buffer electrolyte (pH=7). More importantly, the mechanisms and structure-activity relationships of these transformations were elucidated. Crotyl alcohol was formed on oxide-derived Ag at -0.75 V versus the reversible hydrogen electrode (RHE) with a faradaic efficiency (FE) of 84.3 % (reactant conversion after 75 min electrolysis=9.8 %), which is 1.6 times higher than that on polished Ag foils. The coordinatively-unsaturated sites on oxide-derived Ag surfaces were proposed to facilitate crotonaldehyde adsorption via its oxygen atom in order to promote crotyl alcohol formation. On electrodeposited Fe nanoflakes, crotonaldehyde could be reduced to 1-butanol with an outstanding FE of 60.6 % (reactant conversion after 75 min electrolysis=9.4 %) at -0.70 V vs. RHE. This is nearly 3 times higher than the FE of 1-butanol observed on polished Fe foils at the same potential. More strikingly, the corresponding partial current density of 1-butanol was -9.19 mA cm-2 , which is 43 times higher than that on Fe foils. The presence of tensile strains and grain boundaries on the Fe nanoflakes were elucidated and suggested to activate a concerted reduction of the C=O and C=C bonds in crotonaldehyde to produce 1-butanol selectively.