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 (d=215-840 mu m) 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, N-2 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 degrees 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.

Automated summary

Three zeolites were synthesized in the form of binder-free macroscopic beads using hydrothermal method with anion-exchange resin beads as hard template. The beads consisted of interconnected crystalline zeolite domains, forming a hierarchical porous network. H-Beta beads showed the best catalytic performance in the Friedel-Crafts acylation reaction and could be reused in multiple runs without loss of activity. In continuous-flow tests, H-Beta beads exhibited higher average activity but deactivated more rapidly than the extrudates.