Conversion of Ethanol to Butadiene over Binary MgO-SiO₂ Mixed Oxides Prepared by the Ammonia Evaporation Method

Abstract

The ammonia evaporation method, originally applied for the preparation of highly dispersed silica-supported copper catalysts, was used to synthesize magnesia-silica for the one-step conversion of ethanol to 1,3-butadiene. The MgO-SiO2 catalysts obtained by this method contained a high fraction of magnesium silicate hydrates, which are associated with enhanced butadiene selectivity. These catalysts were benchmarked against those prepared by a conventional wet-kneading method. A Mg/Si molar ratio of 4 was optimal, forming butadiene with 37% yield, which is far superior to the 15% yield obtained with MgO-SiO2 formed by wet-kneading. At 475 °C and a WHSV of 3.2 h−1, a productivity of 0.612 gBD gcat−1 h−1 was measured without the catalyst suffering from deactivation, even after 52 h TOS. The catalysts were characterized by spectroscopic and thermal techniques to elucidate their physicochemical properties and explain the differences in the catalytic performance. The presence of magnesium silicate hydrates gave a balance of surface acidity and basicity, which greatly improved butadiene formation. The open morphology of MgO-SiO2 with vertically arranged platelets and the presence of large pores are proposed to contribute to the stability of the catalyst.

Keywords

• ethanol
• butadiene
• heterogeneous catalysis
• acid-base
• biomass