Cooperative catalytic effects between Brønsted and Lewis acid sites and kinetics for production of methyl methacrylate on SO42−/TiO2-SiO2.

• An efficient and stable SO 4 2−/TiO 2 -SiO 2 catalyst was developed for MMA production. • The Brønsted and Lewis acid site densities and ratios in catalyst can be modulated. • The cooperative catalytic effects between Brønsted and Lewis acid sites were noticed. • The catalytic pathway on such catalyst was confirmed as L-H mechanism. Either the ethylene or isobutene-based route for industrial production of methyl methacrylate (MMA) contains the esterification step between methacrylic acid (MAA) and methanol, therefore it is necessary to develop highly active and stable catalyst. Herein, series of superacid catalysts of SO 4 2-/TiO 2 -SiO 2 were prepared for esterification of MAA with methanol to produce MMA. The Brønsted and Lewis acid site densities and their ratios in SO 4 2-/TiO 2 -SiO 2 could be modulated by controlling the impregnated (NH 4) 2 SO 4 concentration, which were identified by pyridine titration and FT-IR. And no changes in structural skeleton and crystal phase of the SO 4 2-/TiO 2 -SiO 2 during the acid properties regulation process were noticed with FT-IR and XRD. The cooperative catalytic effects between Brønsted and Lewis acid sites were observed through catalytic evaluation. The kinetic studies indicated the catalytic pathway followed L-H mechanism and the activation barrier of forward esterification (48 kJ/mol) was greater than that of reverse hydrolysis (40 kJ/mol) step. [ABSTRACT FROM AUTHOR]