One-pot green synthesis of Fe-ZSM-5 zeolite containing framework heteroatoms via dry gel conversion for enhanced propylene selectivity of catalytic cracking catalyst

Development of a sustainable route for the synthesis of Fe-ZSM-5 zeolites is important due to their diverse applications in different fields. Herein, we report a novel, efficient and an eco-friendly dry gel conversion method to one-pot synthesize Fe-ZSM-5 zeolite containing framework heteroatoms under the conditions that neither the template nor the seed crystal was added. The present strategy not only improves the synthesis efficiency of zeolites, but also reduces the cost and environmental pollution by avoiding using ordinary template. The physicochemical properties of the synthesized samples were analyzed by XRD, N-2 adsorption-desorption, SEM, UV-visible diffuse reflectance, XPS, FT-IR and NH3-TPD techniques. The characterization results revealed that the Fe species in the one-pot synthesized Fe-ZSM-5 zeolite (Fe-ZSM-5-In) mainly exist in the zeolite framework in the form of Fe3+, while those in the Fe/ZSM-5 zeolite prepared by impregnation (Fe/ZSM-5-Im) mostly exist on the surface of the zeolite in the form of non-framework Fe such as oligomeric Fex3+Oy clusters and Fe2O3 particles. Fe-ZSM-5-In possessed enhanced acid amount and better distribution of framework Fe3+ species than Fe/ZSM-5-Im. The results of catalytic performance evaluation show that the propylene yield is improved by the Fe modified ZSM-5 additives due to enhanced acid content and acid strength. Compared with the Fe/ZSM-5-Im additive, the Fe-ZSM-5-In additive has higher propylene yield and lower coke yield owing to its more acid content and lower dehydrogenation activity.