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

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 degrees 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.