Time-Dependent Evolution of 1-Pentene Cracking Pathways on H-ZSM-5 Zeolite: Role of Olefin Adsorption and Diffusion

While temperature and acidity dominate the design of zeolite catalysts for olefin cracking, the role of reaction time as an independent variable governing pathway dynamic remains elusive. This study integrates experimental and simulation methods to unravel the dynamic competition among carbenium ion cracking, thermal cracking and Confined Catalytic Radical (CCR) pathways during 1-pentene cracking on H-ZSM-5 zeolite at 650 °C. Analysis of the optimum performance envelope (OPE) curves for cracking products revealed that, in the initial reaction stage, the CCR mechanism significantly enhances ethylene yield. As the reaction time prolongs, C5+ olefins in the gas phase undergo further cracking on the zeolite surface, markedly increasing the contribution of the carbenium ion pathway. Molecular simulations indicate that C5+ olefins exhibit stronger adsorption capacity but lower diffusion coefficients on H-ZSM-5, and this adsorption–diffusion disparity is a key factor influencing the evolution of 1-pentene cracking pathways. Concurrently, thermal cracking reactions are also enhanced with increasing residence time, which is unfavorable for ethylene formation. This work elucidates the time-dependent evolution of 1-pentene cracking pathways and the regulatory role of intraparticle mass transfer, providing a theoretical basis for optimizing light olefin selectivity through the adjustment of reaction time and catalyst structure.