Mesoscale Distribution of Adsorbates in ZSM-5 Zeolite
Chemical Engineering Science, 2019, 198: 253-259
Wenlai Huang*, Jinghai Li, Zhicheng Liu, Jian Zhou, Chao Ma, Lixiong Wen
Complex distribution of adsorbates can emerge in heterogeneous catalysis due to the compromise among different mechanisms (showing different tendencies of structural evolution) associated with different processes. On two-dimensional catalyst surfaces, all the surfaces are exposed to the gas reservoir (and thus adsorption and desorption processes are accessible to all the surfaces), and we have investigated the effects of adsorption, desorption, diffusion, and reactions on the adlayer structure, and revealed the mechanisms (Huang and Li, 2016). However, in zeolites, only the entrances (or exits) of the pore channels are exposed to the gas reservoir (and thus adsorption and desorption processes are limited there), so the mesoscale behavior might be somewhat different. In this work we explore the influence of adsorption, desorption, diffusion, and reactions on the adsorbate distribution in the ZSM-5 zeolite using kinetic Monte Carlo simulations. Complex distributions of adsorbates (nonlinearly gradient, showing apparent adsorbate shells in some cases) have been revealed, and the channel utilization has been evaluated. The approach and results might be useful to catalyst design, especially determining the optimal thickness of zeolite on a catalyst particle (pellet), since the channel utilization is a measure of effective fraction of the catalyst and is correlated with the practical efficiency of catalysis.
Mesoscale structure, Heterogeneous catalysis, Compromise in competition, Steady state, Zeolite, Channel utilization