BETA zeolite supported on silicon carbide for Friedel-Crafts fixed-bed reactions

Abstract

Beta zeolite coated on a preshaped medium surface area silicon carbide (SiC) carrier was prepared via a hydrothermal synthesis. The SiC support allows the precise control of the macroscopic shape of the final catalyst, which significantly decreases the diffusion pathway of the reactants to the active site. 27Al MAS-NMR analysis revealed that all the aluminum was in a tetrahedral coordination and no trace of extraframework aluminium was observed. The full width at half maximum of the NMR peak was about 10 ppm, which indicates the presence of small zeolite crystals inside the sample. SEM observation has shown that the zeolite homogeneously coated the outer surface of the silicon carbide extrudate support with different size and shape and random orientation. The existence of a layer of silica and silicon oxycarbide on the surface of the support allows a strong anchoring of the coated zeolite which prevents the loss of the deposited zeolite during handling and operation. The as-prepared catalyst exhibits a high catalytic activity in the benzoylation of anisole in a fixed-bed configuration. In addition, the catalyst was extremely stable, as no deactivation was observed after several hours of test, whereas bulk zeolite exhibits a strong deactivation with the time mainly due to the formation of carbonaceous residues inside the channel network.