Surface hydroxyl engineering induced construction of isolated Zr sites for selective methyl methacrylate production

Significant attention is paid to methyl methacrylate (MMA) synthesis via direct aldol reaction on supported Cs-based catalysts; however, the structure of active sites is still unclear. Herein, the structural sensitivity of Zr sites toward MMA production through aldol condensation of methyl propionate with formaldehyde on Cs/Zr/SiO 2 was identified, which was affected by surface hydroxyl groups on SiO 2 . Isolated hydroxyl groups were discovered to induce the formation of well-defined Zr sites, which facilitated MMA formation, while the dimeric Zr species led to the generation of undesired methylacrolein (MAL) byproduct. It was demonstrated that a higher proportion of medium and strong Lewis acid sites could suppress MAL production through sequential H-transfer hydrogenolysis and condensation reaction. As a result, the selectivity and formation rate of MMA could be promoted by ~30% and ~2.5 folds after Zr site modification. Therefore, the local structure of active components is critical to the regulation of catalytic performance in MMA production.