Studies on Sr–Zn mixed oxides as acid–base bifunctional catalysts for the selective carbonylation of glycerol to glycerol carbonate

Abstract

Transforming glycerol (GLY) into high-value chemicals is essential for enhancing the economic viability and sustainability of the biodiesel industry. This study explores the conversion of GLY into glycerol carbonate (GLC) using dimethyl carbonate (DMC) as a carbonylating agent under solvent-free conditions over Sr–Zn mixed oxide catalysts. A series of Sr–Zn (SZ) mixed oxide bifunctional catalysts with different Sr/Zn molar ratios were prepared via a co-precipitation method. The presence of ZnO in the SrO lattice stabilised strontium within the lattice, generating synergistic acid–base bifunctional sites with optimum amount of acdic/basic strength and surface area. The as-prepared Sr–Zn mixed metal oxides outperformed individual Sr and Zn oxides in terms of activity and stability. In contrast to the physical mixture of both metal oxides, the synergistic interaction of SrO and ZnO in the mixed oxide catalyst resulted in excellent glycerol carbonylation. The catalyst with a Sr–Zn molar ratio of 2 : 1 (SZ 21) exhibited excellent performance with 95% GLC yield and almost 100% selectivity. The SZ 21 catalyst also demonstrated consistent activity with remarkable resilience to impurities in crude glycerol and demonstrated exceptional stability during the studied six recycles. The kinetic study of GLY carbonylation showed a pseudo-first-order reaction kinetics.