MgO−SiO2 Catalysts for the Ethanol to Butadiene Reaction: The Effect of Lewis Acid Promoters

Abstract

MgO−SiO2 samples, having the composition of natural talc (NT), were obtained by co-precipitation (CP) and wet kneading (WK) methods. The materials were used as catalysts of the ethanol-to-1,3-butadiene reaction. ZnO, Ga2O3 and In2O3 were tested as promoters. The catalyst WK gave the highest 1,3-Butadiene (BD) yield among the non-promoted catalysts because of the high specific surface area and strong basicity. Results suggested that over the neat WK catalyst the acetaldehyde coupling to crotonaldehyde was the rate-determining process step. Formation of crotyl alcohol intermediate was substantiated to proceed by the hydrogen transfer reaction between crotonaldehyde and ethanol. The crotyl alcohol intermediate becomes dehydrated to BD or, in a disproportionation side reaction, it forms crotonaldehyde and butanol. The promoter was found to increase the surface concentration of the reactant and reaction intermediates, thereby increases the rates of conversion and BD formation. The order of promoting efficiency was Zn>In>Ga.