Core–shell Pd/ZSM-5@ZIF-8 membrane micro-reactors with size selectivity properties for alkene hydrogenation

Abstract

A well-designed Pd/ZSM-5@ZIF-8 core–shell structure has been prepared by application of a combination of seed-induction synthesis strategy and self-assembly synthesis techniques. First, uniform ZSM-5 particles with micron size and high crystallinity were prepared from organic-template-free gel systems containing 200nm ZSM-5 seeds and exchanged with Pd(NO3)2 aqueous solution. Then incompatibility between the Pd/ZSM-5 core material and ZIF-8 shell precursor was circumvented by surface modification using a layer by layer self-assembly of polyelectrolyte, followed by a subsequent two-step temperature synthesis process inducing the formation of continuous and well-intergrown ZIF-8 shell. Thickness of ZIF-8 shell can be simply tuned by monitoring the assembly cycles. Furthermore, hydrogenations of 1-hexene and cyclohexene were chosen as model reactions to evaluate the catalytic behavior of the Pd/ZSM-5@ZIF-8 core–shell architecture and tert-dodecylthiol was used as a poison to test its anti-poisoning ability. Results show that such core–shell architecture exhibits excellent poison resistance and selectivity control properties for the hydrogenation reactions and can be potentially used as a membrane reactor in the field of heterogeneous catalysis.