Remarkable catalytic performance of newly synthesized H-SSZ-23 zeolite in methanol to olefin process

Abstract

Methanol-to-olefin technology, designed to produce light olefins from methanol, often encounters issues with rapid catalyst deactivation due to diffusion challenges and coke build-up. The structure of zeolite significantly influences both the distribution of olefin products and the stability of the catalyst. In this research, H-SSZ-23 zeolite synthesized by hydrothermal method in two different OH⁻ and F⁻ mediums investigated as a novel catalyst in MTO process. Additionally, conventional H-SSZ-13 zeolite was synthesized with the identical conditions to compare the performance of H-SSZ-23 zeolite with the literature. To determine the physicochemical properties of the catalysts, various characterization methods were employed, including XRD, FESEM, ICP, BET-BJH, FTIR, NH3-TPD, and TG/DTG analyses. The methanol conversion and product selectivity of the synthesized zeolites were tested in the MTO reaction at temperatures ranging from 350 to 450 °C, under atmospheric pressure with a methanol weight hourly space velocity (WHSV) of 1.2 h⁻¹. The seed-assisted synthesis method yielded pure H-SSZ-23 (STT) and H-SSZ-13 (CHA) zeolite phases with distinct morphologies, textural properties, surface acidity and catalytic performance in the MTO process. Among the findings, the H-SSZ-23 zeolite synthesized in OH⁻ medium having 99 % methanol conversion, 70 % light olefins selectivity and about 300 min stability (80 % initial conversion) at 450 °C exhibited best performance with improved stability and reduced coke formation in the MTO process. This superior stability can be attributed to its unique structure with smaller particle size at nanoscale, increased mesopore volume, larger pore diameter and milder acidity compared to H-SSZ-13 (CHA) zeolite.