From Framework to Extra-framework, Synthesis of Encapsulated Fe-ZSM-5 Zeolite with Enhanced Catalytic Cracking

Abstract

With the diversification of hydrocarbon feedstocks, improving selectivity of light olefins at high conversion has become a technical bottleneck in Fluid Catalytic Cracking (FCC) processes. The rational design of bifunctional catalysts, which possess both acidic sites and dehydrogenation sites is crucial for enhancing the activity for catalytic cracking of naphtha to selectively produce light olefins. In this study, we synthesized ZSM-5 zeolite (SiO₂/Al₂O₃=35~40) with Fe incorporated into ZSM-5 framework, as confirmed by XPS and H₂-TPR characterizations, in the presence of triethanolamine without the use of an organic template. Interestingly minimal triethanolamine was found to be trapped within the ZSM-5 zeolite, as demonstrated by TG-MS and ¹³C CP/MAS NMR results. Most of triethanolamine remained in the filtrate, facilitating the easy reuse of organic ligands. Furthermore, hydrothermal treatment resulted in the formation of highly dispersed extra-framework FeO_x species with dehydrogenation capability within the channels of the ZSM-5 zeolite, significantly enhancing the conversion and olefin yields of catalytic cracking with n-tetradecane, ethylcyclohexane and naphtha as feedstocks.