Construction of active Cs and Zr sites for Selective production of methyl methacrylate on Cs/Zr/SiO2 catalyst

Acid-base bifunctional Cs-Zr supported SiO 2 exhibit high catalytic performance on aldol condensation of methyl propionate (MP) and formaldehyde (FA) toward methyl acrylate (MMA). However, the effect of structural configuration of surface active sites on the formation rate and selectivity of MMA remains unclear. In this study, a surface engineering strategy was proposed to directionally induce the formation of catalytically active centers. Comprehensive characterizations were performed to identify the structural configuration of surface active Cs and Zr sites and their influence on MMA production in combination with catalytic evaluation. It was discovered that the increased density of isolated hydroxyl groups (≡Si-OH) on SiO 2 support after calcination treatment promoted the formation of well-defined Si-O-Zr and Si-O-Cs structures, corresponding to the medium strong acid and weak base sites. The acid-base properties and their balance of as-prepared Cs/Zr/SiO 2 catalyst could be controllably modulated by the surface hydroxyl density and Cs (Zr) loading. These highly dispersed Cs and Zr species generated through the strong interaction with hydroxyl groups facilitated the production of MMA while suppressed the undesired Methylacrolein (MAL). Consequentially, the formation rate and selectivity of MMA could reach up to 0.91 mmol/h/g Cat. and 94.3 % on the optimal 1.5Cs/0.25Zr/SiO 2 catalyst. Further mechanistic studies using In-situ DRIFT revealed the catalytic pathway toward MMA and MAL, confirming the activation of MP was the kinetic-relevant step.