Optimized bifunctional CuNiMgAl catalysts for efficient synthesis of the renewable bioproduct glycerol carbonate

Abstract

This paper presents a novel technology for converting glycerol, a byproduct of the biodiesel industry, into glycerol carbonate, a high-value bioproduct. The effect of calcination temperature on the synthesis of quaternary Cu-Ni-Mg-Al catalysts (MMO-Cu15Ni15-Tz) and their application in the transesterification reaction was investigated. Glycerol conversion remained largely unaffected by calcination temperature; however, selectivity toward glycerol carbonate was influenced. Physicochemical analyses showed increased crystallinity and spinel phase formation with higher calcination temperatures, resulting in lower oxide dispersion and decreased specific surface area. Nonetheless, the preservation of nanolayer morphology and increased pore diameter maintained high conversion rates at elevated temperatures. X-ray photoelectron spectroscopy (XPS) confirmed Cu2+ interactions with the MgAl matrix and the formation of a solid solution. Ultraviolet-visible diffuse reflectance (UV-visible DR) spectroscopy indicated the dominance of octahedrally coordinated Cu2+ and spinel phases at the highest temperature. The MMO-Cu15Ni15-T450 catalyst exhibited the highest concentration of strong basic sites and the lowest concentration of very strong basic sites. Acid–base characterization suggested that very strong basic sites and abundant acid sites promote glycidol formation by glycerol carbonate decarboxylation. Calcination at 450 °C was identified as optimal, maximizing glycerol carbonate yield while minimizing byproduct formation. This work supports a biorefinery approach aligned with circular economy principles to reduce the environmental impact of biodiesel production through the use of cost-effective catalysts and efficient processes.