Cascade aldol condensation of an aldehyde<i>via</i>the aerobic oxidation of ethanol over an Au/NiO composite

Abstract

Synthesis of liquid biofuels (C₁₁-C₁₃) from cellulosic ethanol is regarded as a promising and versatile protocol. In this study, oxide-supported nanogold catalysts exhibit good catalytic performance in ethanol conversion with cinnamaldehyde and finally give rise to the C₁₁-C₁₃ hydrocarbon. High selectivity (70%) for C₁₁-C₁₃ hydrocarbons is achieved over Au/NiO <i>via</i> a one-pot cascade reaction, <i>viz.</i> cross-aldol condensations in the presence of oxygen and base (K₂CO₃) and then full hydrodeoxygenation with hydrogen gas. EtOH-TPD and TGA analyses show that the ethanol is activated to acetaldehyde (CH₃CHO*) over the surface oxygen vacancies of the NiO support. The CH₃CHO* then reacts with cinnamaldehyde at the interfacial perimeter of the Au/NiO composite during the cascade reactions, as evidenced by comparison of the catalytic performance with that over another oxide-supported Au NP, chemo-adsorption investigations, and <i>in situ</i> infrared spectroscopy investigations. This work may provide new guidelines for designing efficient catalysts to convert bioethanol into biofuels with high energy density.