A Multipore Model for Heterogeneous Catalytic Polymerization: Structure–Performance Relationships

Abstract

A novel single-particle model is developed for the physicochemical processes involved in the heterogeneous catalytic polymerization. The model considers the reaction kinetics together with the detailed initial pore structure and explicitly describes the support fragmentation. It captures some of the most widely observed morphological features of heterogeneous catalysis for both before and after starting fragmentation, including the possibility of occurrence of both known fragmentation mechanisms. All the monomer mass conservation equations are solved using a robust semianalytical approach. The results show that the catalyst pore structure, which can be tuned during chemical preparations, has a vital role in determining the catalyst performance through changing the contribution of each of the two fragmentation mechanisms in the overall fragmentation process and that decreasing the propagation rate constant and/or increasing diffusion coefficient intensifies the continuous bisection mechanism. A potential fragmentation index is proposed in order to relate the fragmentation phenomenon to structural features of the catalyst. By defining a weighted average fill factor, it is shown that the fragmentation index is in fact a measure of how much the pores closer to the center relative to the pores closer to the surface are filled up at the fragmentation moment.