An analysis of the chemical, physical and reactivity features of MgO–SiO2 catalysts for butadiene synthesis with the Lebedev process

Abstract

New insights into the transformation of ethanol to butadiene over MgO–SiO₂ catalysts, prepared by means of the sol–gel technique, have been gained via characterization, catalytic tests, and in situ infrared diffuse reflectance spectroscopy. Catalysts with low Si-content, i.e., with a Mg/Si atomic ratio in the range between 9 and 15, gave superior butadiene yields, because of the proper combination of strong basic sites, required for ethanol activation, and a moderate number of medium-strength acid sites, needed for the dehydration of intermediately formed alkenols to butadiene. A model of the medium-strength, Lewis-type acid sites, consisting of Mg²⁺ cations with neighbouring Si⁴⁺ atoms, has been proposed; these sites are converted into Brønsted sites in the presence of water, a co-product of the multistep transformation of ethanol into C₄ molecules.