Conventional hydrothermal synthesis of nanostructured H-ZSM-5 catalysts using various templates for light olefins production from methanol

Abstract

High-silica H-ZSM-5 catalysts (Si/Al = 200) were successfully synthesized using the conventional hydrothermal method under a static condition in the presence of tetrapropyl ammonium hydroxide (TPAOH), tetrapropyl ammonium bromide (TPABr), n-butyl amine (NBA) and morpholine (MOR) as the structure-directing agents. The influence of the templates on the crystal size, surface area, pore volume, morphology and surface acidity of H-ZSM-5 catalysts was characterized by XRD, FE–SEM, BET, FT–IR and NH3-TPD techniques. The catalytic performance of the H-ZSM-5 samples in the methanol to olefins (MTO) reaction was conducted in a fixed-bed reactor at 480 °C, atmospheric pressure and methanol WHSV of 0.9 h−1 using methanol to water weight ratio of unity in the feed. The FE–SEM micrographs revealed that only ZSM-5 samples prepared with TPAOH and TPABr exhibited the MFI-typical hexagonal and spherical-shaped morphologies. The XRD patterns indicated higher crystallinity for the catalyst synthesized using TPABr. Also, this catalyst exhibited the highest acidity and acceptable surface area. All the samples illustrated activity in the MTO reaction but the products selectivity especially for the propylene and other light olefins was extremely different. The prepared sample with TPABr as the template displayed the highest methanol conversion (99.37%) and propylene selectivity (37.59%).