ZSM-5@Sil-1 core shell: Effect of synthesis method over textural and catalytic properties

Abstract

A modified technique of epitaxial growth employed to produce “core-shell” catalysts coating microporous ZSM-5 with a layer of Silicalite-1 is presented in this paper. The aim was to passivate surface acidity of a ZSM-5 zeolite, in the view of potential limitation of surface effect generally responsible for coke formation. Core-shell catalysts have been synthesized starting from a ZSM-5 core with Si/Al = 25. Two different hydrothermal Silicalite-1 synthesis were performed: one using the ZSM-5 as made-form and the second using the ZSM-5H+-form as core. This allowed to investigate the effect of the organic template, filling the pores of the core, on the shell growth mechanism. Coating procedure lasted 24 h and it was repeated twice to increase Silicalite-1 thickness. All catalysts were tested for the reaction of methanol dehydration to DME in an atmospheric system at 180–240° and time on stream tests were carried out to analyse the stability of the samples. Considering the catalytic performances in terms of methanol conversion, DME selectivity and deactivation, core-shell catalysts, synthetized using an as-made form core, exhibited interesting performances, resulting from a more controlled growth of the passivating layer. These materials could constitute valid option for hybrid (Metal-Zeolite) catalyst, where the reduction of surface acidity could better stabilize the metallic function.