Optimizing zeolitic hierarchical pore structure to boost the direct conversion of aromatics from syngas over the iron-based/zeolite bifunctional catalysts

Abstract

The utilization of iron-based/ZSM-5 bifunctional catalysts for converting syngas to aromatics (STA) has garnered significant interest because of its cost-effectiveness. This study aims to elucidate the regulatory mechanism of zeolitic pore structure on the performance of the bifunctional catalyst in STA reaction. The relationship among the mesoporosity and mesoporous diameter of hierarchical ZSM-5 zeolite component, product distribution, and catalyst stability is investigated through a range of analyses techniques, including XRD, SEM, TG, Raman, N2-adsorption and desorption. The results demonstrate that as the mesoporosity of zeolite increased to 78.9%, the lifetime of the iron-based/ZSM-5 bifunctional catalyst extended beyond 96 h and maintained the aromatics selectivity over 40% at 2 MPa, 320 °C, and 3000 h−1. This outcome can be attributed to the role of high mesoporosity in restraining coke formation in zeolites. Moreover, the reduction in mesopore size from 11.1 to 5.8 nm results in an increased aromatics selectivity from 39.6% to 43.4%, and the fraction of light aromatics rose from 48.8% to 54.5%, indicating that small mesopore size can also expedite the production of aromatics, particularly light aromatics. It is thus concluded that the improvement of aromatics selectivity and stability of iron-based/ZSM-5 bifunctional catalysts in STA reaction can be achieved by increasing the mesoporosity and decreasing the mesopore size of the zeolite component.