Highly active and selective binary MgO–SiO2 catalysts for the production of 1,3-butadiene from ethanol
A series of magnesia–silica binary composite catalysts with different molar ratios were prepared using various preparation methods and evaluated for the one-step production of 1,3-butadiene (BD) from bio-ethanol. The MgO–SiO2 catalyst prepared by wet-kneading is distinguished from the samples prepared by other methods by its superior activity. An exceptionally high productivity of butadiene with the high ethanol conversion of 95% and BD selectivity of 77% was obtained over wet-kneaded hierarchical flower-like MgO nanostructures with the catalytic material made up of SiO2 spheres (with a MgO : SiO2 molar ratio of 65 : 35 at 450 °C and an WHSV of 4.1 h−1), which translates into an unprecedented BD yield of 0.025 mol gcat−1 h−1. The as-prepared catalysts were characterized by XRD, FESEM, BET, FT-IR, UV/vis, CO2-TPD and NH3-TPD. The Mg precursor used and the preparation method are found to influence the extent of MgO and SiO2 interactions during preparation, as estimated by various techniques, which, in turn, was found to correlate with the catalytic performance. A subtle balance of surface acidity/basicity was found to be necessary to achieve a high butadiene yield which can be obtained by variation of MgO : SiO2 ratios in wet-kneaded samples. In view of the difference in catalytic activity and the physicochemical properties of the MgO–SiO2 composite catalysts, the Si–O–Mg chemical bond formed by the strong MgO and SiO2 interaction is suggested to be essential for the balanced surface acid/base sites in relation to the strong interaction between MgO and SiO2 and the consequent high catalytic performance.