Critical role of dimensional pore structure in the efficient methyl acrylate production via one-step vaporous aldol reaction

Coal-based aldol condensation of methyl acetate with formaldehyde on Cs-based catalyst is a promising atom-economic route for methyl acrylate production, where the pore structure plays a critical role in addition to the acid and base properties. Herein, series of Cs-Zr-Al/SiO 2 catalysts with similar acid-base properties but different porous structure, were synthesized via hydrothermal and co-impregnation method for synthesis of methyl acrylate. The physicochemical characteristics of as-prepared catalysts were comprehensively analyzed by physical N 2 adsorption and desorption isotherms, XRD, and CO 2 /NH 3 -TPD. The structures of disordered mesopores, two-dimensional hexagonal straight channels, three-dimensional cubic cage pores, and three-dimensional interconnected pores exhibit significant effect on the reactant/product diffusion and transformative process. In situ DRIFTS revealed the reactants and product show the Knudsen diffusion behavior, with diffusion coefficients showing strong positive correlation to pore diameter, indicating that mass transfer efficiency is pore-structure-dependent. Accelerated diffusion in the optimal pore structure would enhance methyl acetate conversion while improve selectivity for methyl acrylate diffusion by suppression of side reactions. Among which, the Cs-Al-Zr/SiO 2 (KIT-6) featuring a three-dimensional interconnected pore structure with an average diameter of 7.4 nm, demonstrated the exceptional performance in the aldol condensation reaction, achieving 25.9 % methyl acetate conversion, 92.7 % methyl acrylate selectivity, and a space–time yield of 2.69 mmol MA /g Cat /h. Furthermore, it showed considerable catalytic stability and regeneration capability.