Solventless Glycerol Etherification to Di- and Tri-Glycerol over Mg-La Mixed Oxides Derived from Layered Double Hydroxides

Mg–La mixed metal oxides derived from layered double hydroxide (LDH) precursors were synthesized via coprecipitation and evaluated as heterogeneous catalysts for solventless glycerol etherification to short-chain polyglycerols. The influence of Mg/La molar ratio on the structural, textural, and catalytic properties of the catalysts was systematically investigated using XRD, BET, SEM-EDX, FTIR, TPD-CO2, TPD-NH3 and ICP-OES analyses. XRD confirmed the formation of La2O2CO3 phases, while CO2-TPD analysis revealed the presence of abundant medium-to-strong basic sites. Among the synthesized catalysts, Mg0.25La0.75O2 exhibited the highest basic site concentration (6830 µmol g−1) and superior catalytic performance due to the possible cooperative interaction between Mg- and La-derived sites. Under optimum reaction conditions of 220 °C, 8 h, and 2 wt% catalyst loading, the catalyst achieved 90% glycerol conversion with 70% diglycerol selectivity, 23% triglycerol selectivity, and 84% combined diglycerol and triglycerol yield. Reaction temperature, catalyst loading, and reaction duration significantly influenced oligomer distribution and catalyst performance. Reusability studies demonstrated acceptable catalyst stability for up to four cycles before gradual deactivation caused by oligomer deposition and metal leaching. The results highlight Mg–La mixed oxides as promising catalysts for sustainable solvent-free glycerol valorization, while demonstrating a scalable and environmentally benign strategy for maximizing lower-degree polyglycerol production within shorter reaction durations and reduced processing cost.