Friedel-Crafts acylation of anisole with acetic anhydride over single- to multiple-layer MWW zeolites: Catalytic behavior and kinetic mechanism

Abstract

Numerous efforts have been dedicated to develop solid acid catalysts with higher activity and stability replacing the homogeneous catalysis for Friedel-Crafts (FC) acylation reaction. In this study, single- to multiple-layer MWW zeolites are employed as well-defined model catalysts to investigate the influencing mechanism of microscale structure of MWW zeolites on the kinetics for acylation of anisole with acetic anhydride. It is found that the acylation of anisole is solely carried out on the external acid sites of MWW zeolites and follows Langmuir-Hinshelwood mechanism. The single-layer MWW (SL-MWW) with more external acid sites exhibits lower catalytic activity for acylation of anisole in batch reaction, whereas the recycle stability of SL-MWW is clearly higher than that of multiple-layer MWW (ML-MWW). Kinetics results reveal that a large equilibrium constant of product adsorption together with the confinement effect within 12MR pockets on surface of SL-MWW results in difficult desorption of product and small rate constant. Therefore, the favorable mass-transfer and diffusion of SL-MWW is restrained in batch reaction and at low temperature condition. Based on these findings, the continuous flow fixed-bed process under an elevated temperature (493 K) was conducted to underline the structural advantages of SL-MWW zeolite. The lifetime of SL-MWW can reach to 300 h in the optimal reaction conditions, which is potential catalyst for industrial application in the field of FC acylation reactions.