Environmentally benign synthesis of hydrotalcite-like materials for enhanced efficiency of aldol condensation reactions

Abstract

MgAl hydrotalcites (HTCs) are promising catalysts for biomass valorization applications. However, their production suffers from excessive wastewater generation while their application is limited by insufficient accessibility of active sites. Here, we change the paradigm of hydrotalcite synthesis by replacing the traditional co-precipitation by MgO impregnation with aluminum isopropoxide followed by calcination and (re)hydration. This synthesis affords surface HTC phase ensuring excellent accessibility to Brønsted basic sites. HTC supported on MgO surface (bulk Mg/Al = 20) exhibited same conversion and selectivity in aldol condensation of furfural with acetone as conventional HTC (Mg/Al = 3). Besides maximized efficiency of aluminum use to generate accessible Brønsted basic sites, the catalyst was stable in several consecutive catalytic experiments, if optimal rehydration conditions were applied. Moreover, the use of large quantities of water required for the co-precipitation-based method was avoided. This makes the new method superior also from green synthesis and sustainability point of view.