Microwave-assisted catalytic conversion of glycerol to lactic acid using a synergistic trimetallic oxide (NiO-CuO-ZnO) system

The catalytic conversion of glycerol into lactic acid offers a sustainable route for biomass valorization, yet achieving high selectivity under mild conditions remains challenging. Using a dehydrogenation-rearrangement route, we created a synergistic trimetallic oxide (NiO-CuO-ZnO) catalyst for microwave-assisted glycerol transformation. The optimized composition (NiO₁CuO₂ZnO₁) achieved ∼98% glycerol conversion and ∼90% lactic acid selectivity in alkaline media. Physicochemical characterization revealed distinct catalyst roles: Cu sites drive dehydrogenation, Ni stabilizes reaction intermediates, and ZnO provides basic sites critical for glycerol activation. Quantitative XRD, FTIR and XPS confirmed phase purity, crystallite size, and relevant surface species. Using response surface methods and ANOVA validation, experimental data demonstrated significant agreement with model predictions. According to kinetic study, microwave irradiation decreases apparent activation energy due to localized interfacial heating and increased energy coupling with polar molecules. Reusability tests verified structural stability and preservation of active sites using XRD and FTIR, with very little metal leaching reported. Collectively, our findings demonstrate that rational design of redox-basic synergistic catalysts, combined with microwave-assisted processing, provides an efficient and sustainable pathway for glycerol valorization to lactic acid.