Flexible Modulation of Si–O–Cs Sites in a Cs/Zr-SiO<sub>2</sub> Bifunctional Catalyst for the Efficient Conversion of Methyl Propionate and Formaldehyde to Methyl Methacrylate
Junyang Liu, Gang Wang, Guoliang Zhang, Jie Li, Chunshan Li, Zengxi Li
Abstract
The design of efficient Cs-based supported catalysts is significantly crucial for methyl methacrylate (MMA) synthesis via direct aldol condensation. Herein, a type of Cs/Zr-SiO 2 bifunctional catalyst with atomic Cs dispersion and ZrO 2 nanoparticle sites was prepared through the strong electrostatic adsorption (SEA) method. A series of characterizations, including HAADF-STEM, XRD, XPS, MAS NMR, CO 2 /NH 3 -TPD, and Py-IR, were performed to measure the physicochemical properties of the as-prepared catalyst samples. The Si–O–Cs centers, Si–O–Zr sites, and ZrO 2 nanoparticles were identified as Lewis base and acid sites for the catalytic activation of methyl propionate and formaldehyde, respectively. The acid–base properties and their balance could be controllably modulated by Cs and Zr loadings to suppress undesired byproducts. Specifically, as high as 70.0% conversion of methyl propionate, with around 91.8% selectivity for MMA, could be achieved on the optimal catalyst, with Cs loading remarkably decreased by more than twofold compared with that prepared by the traditional incipient-wetness impregnation method.