Zr-Incorporated SiO₂-Supported Cs for Effective Production of Methyl Methacrylate via One-Step Aldol Condensation

Modification of supported Cs-based catalysts has stimulated researchers' interests, considering their effective catalytic performance in methyl methacrylate (MMA) production via one-step aldol condensation. Herein, we developed a series of Zr-incorporated SiO2-supported Cs (Cs/Zr-SiO2) catalysts using sol–gel in combination with solvothermal and impregnation methods. The structure and physicochemical properties were analyzed systematically by employing multiple characterization techniques, which guided the optimization of synthesis parameters such as Si/Zr molar ratio, prehydrolysis time, and Cs loading. The effects of catalyst structure, acid–base properties and their balance, and the chemical state of Cs and Zr species on the catalytic performance were systematically correlated. Results indicate that Zr was incorporated into the SiO2 framework with a four-coordinated configuration to form Si–O–Zr structures to act as Lewis acid sites, while the Cs component provides base sites through the formation of Cs–O–Si configurations. As a result, the methyl propionate (MP) conversion could reach up to 34.9% with MMA selectivity of 88.4%, representing 10–12% enhancement over the traditional impregnation method. In situ IR spectroscopic insights elucidated that the activation of formaldehyde and MP proceeded severally on the Si–O–Zr and Cs–O–Si sites, which seemed to be more efficient than those on an impregnation-prepared sample. Kinetic studies determined the activation energy of 115 kJ/mol, with reaction orders of 1.04 and 1.14 for MP and FA, respectively. In addition, the catalyst exhibited excellent regeneration and recycling behavior during the long-term stability test, and the initial activity of sample deactivated due to carbon deposition could be easily recovered after thermal treatment.