Agar-Assisted Engineering of Defect-Rich MgAl Mixed Oxides for Enhanced Glycerol Transesterification

Over the past decades, Mg-Al mixed-metal oxides have been extensively employed as catalysts in diverse reactions owing to their compositional versatility, structural tunability, and tunable acid-base properties. Nevertheless, conventional synthesis approaches, such as coprecipitation, present notable limitations, including sustainability concerns, operational complexity, and limited control over intrinsic defect density. Since these features play a key role in determining catalytic performance, recent efforts have increasingly focused on engineering defect-rich structures. In this context, we report, for the first time, the synthesis of a Mg-Al mixed oxide via a polysaccharide-assisted route using agar-agar as a polymerizing agent. The resulting material was comprehensively characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), N 2 physisorption (BET surface area), CO 2 temperature-programmed desorption (CO 2 -TPD), CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS), electron paramagnetic resonance (EPR), attenuated total reflectance spectroscopy (ATR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), enabling an in-depth analysis of its structural, textural, and surface properties. The catalytic performance of the material was evaluated for the transesterification of glycerol with dimethyl carbonate, an industrially relevant process, and compared against a coprecipitated analogue. The polysaccharide-derived oxide exhibited enhanced catalytic activity, which can be attributed to its higher surface area, tailored morphology, and increased density of oxygen vacancy defects. Moreover, the improved performance is associated with a synergistic effect between Brønsted-basic sites and Lewis-acidic centers, highlighting the potential of this sustainable synthetic strategy for the design of advanced catalytic materials.