Binder-free zeolite Beta beads with hierarchical porosity:Synthesis and application as heterogeneous catalysts for anisole acylation

Three zeolites (H-Beta, H-ZSM-5 and H-Y) were synthesized in the form of binder-free macroscopic beads (350-800 µm) using a hydrothermal method employing anion-exchange resin beads as hard template. The beads obtained after removal of the hard template by calcination consisted of crystalline zeolite domains connected with each other to form a hierarchical porous network in which the zeolitic micropores are accessible through meso- and macropores, as proven by characterization with XRD, N2 physisorption, SEM, and TEM. The composition, the nature and amount of acid sites and the degree of hydrophobicity of these beads were investigated by means of XRF, solid-state NMR, pyridine-FTIR and TGA. The zeolite beads were tested as heterogeneous catalysts in the Friedel-Crafts acylation of anisole with acetic anhydride to produce para-methoxyacetophenone. H-Beta-Beads displayed the best catalytic performance with 95% conversion of acetic anhydride and 76% yield of para-methoxyacetophenone in a batch reactor test (90 °C, 6 h). Next, the catalytic performance of H-Beta-Beads was compared in both batch and continuous-flow mode to extrudates prepared by mixing zeolite Beta powder with either kaolin or bentonite binders. H-Beta-Beads outperformed the extrudates in batch-mode reactions and could be reused in multiple runs without discernible loss of activity. In the continuous-flow test, H-Beta-Beads demonstrated higher average activity but deactivated more rapidly than the extrudates