(Co2+,Pd2+)2SiO4Pd0 Olivine: Influence of Lewis Acids on Heterogeneous Heck–Mizoroki Catalysis

This study investigates the influence of Lewis acids on a novel stratified (Co2+,Pd2+)2SiO4-Pd0 olivine catalyst for the Heck–Mizoroki coupling of iodobenzene and methyl acrylate. Comprehensive characterization (ICP-OES, Raman, P-XRD, XPS) confirms the successful synthesis of a material with surface-incorporated Pd2+ and bulk Pd0 nanoparticles within a Co2SiO4 matrix. The promoter-free system with triethylamine base achieved the highest initial rate of 3.92 × 10−7 mol.s−1 with an average rate of 1.18 × 10−7 mol.s−1, despite a 30 min induction period. However, ZnCl2, the weakest acid, showed the most substrate activation and lowered the induction period to 10 min, while AlCl3 also reduced the induction period to 20 min. FeCl3 showed the poorest performance, attributed to redox-mediated site poisoning rather than hydrolysis. Selectivity over the catalyst was maintained at >99 mol% towards methyl cinnamate irrespective of the Lewis acid or base used. However, recycling of the catalyst led to a gradual decrease in selectivity toward methyl cinnamate from >99 mol% to ~94.6 mol% over three cycles, while conversion remained consistently high at >99 mol% across all cycles, indicating that the catalyst’s primary activity was largely preserved despite surface evolution toward side-product formation. Lewis acids were found to function primarily as surface modifiers and/or productive substrate activators, with stronger Lewis acids also targeting the olivine framework, as seen from the preferential leaching of Co relative to Pd.