Highly active and selective binary MgO–SiO2 catalysts for the production of 1,3-butadiene from ethanol

Abstract

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 g_cat⁻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.