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

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 degrees C and a WHSV of 3.2 h(-1), a productivity of 0.612 g(BD) g(cat)(-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.