Effects of Beta particle size on Diels–Alder conversion of 2,5-dimethylfuran and acrylic acid to para-xylene

Abstract

The process of producing para-xylene (PX) from 2,5-dimethylfuran (DMF) via Diels-Alder (D-A) cycloaddition over Beta zeolites was recognized as a green and sustainable pathway for PX production. Theoretically, small zeolite particles need to be synthesized to mitigate mass transfer limitations caused by their inherent microporous structure, but particle size changes simultaneously alter crystallinity, acidity, and pore characteristics. The effects of these factors on the Diels-Alder (D-A) cycloaddition reaction have not yet been fully elucidated. In this study, Beta zeolites with average particle sizes of 100 nm, 180 nm, 450 nm, and 760 nm were prepared and applied to the D-A cycloaddition of DMF reaction. All Beta zeolites exhibited a polycrystalline structure composed of nanocrystallites and featured both micropores and mesopores. The turnover frequency (TOF) of Beta zeolite with 760 nm particle size was approximately one-third that of the other three zeolites at 160 °C, and its apparent activation energy (E_a) for PX formation was significantly lower than that of the smaller-particle zeolites. The reduced activity and E_a were primarily attributed to significant mass transfer limitation in larger-particle zeolites, with this limitation mainly originating from lengthened diffusion paths, diminished mesoporosity, mismatch in structure, and micropore alignment by internal grain boundaries. Within the particle size range where mass transfer limitations were eliminated, excessively small particle size can also detrimentally impact catalytic performance, owing to easier crystallinity reduction during the reaction.