Influence of acid–base properties on the Lebedev ethanol-to-butadiene process catalyzed by SiO2–MgO materials†
The Lebedev ethanol-to-butadiene process entails a complex chain of reactions that require catalysts to possess a subtle balance in the number and strength of acidic and basic sites. SiO2–MgO materials can be excellent Lebedev catalysts if properly prepared, as catalyst performance has been found to depend significantly on the synthesis method. To assess the specific requirements for butadiene production in terms of active sites and to link their presence to the specific preparation method applied, five distinct SiO2–MgO catalysts, prepared by wet-kneading and co-precipitation methods, were thoroughly characterized. The amount and strength of the acidic (pyridine-IR and NH3-TPD) and basic (CDCl3-IR and CO2-TPD) sites of the materials as well as the overall acid/base properties in the liquid phase (Hammett indicators) were determined. The number of acidic and strong basic sites could be correlated with the extent of ethylene and diethyl ether by-product formation. The best performing catalysts are those containing a small amount of strong basic sites, combined with an intermediate amount of acidic sites and weak basic ones. These results thus provide further insight into the relation between the amount and strength of acidic/basic sites, preparation method and catalytic performance.