Catalytic cracking of n-hexane to light alkene over ZSM-5 zeolite: Influence of hierarchical porosity and acid property

ZSM-5 is active in n-hexane cracking to light alkenes, but with the disadvantage of fast deactivation. A long lifetime ZSM-5 with high activity and anti-carbon deposition performance was of great concern for industrial application. The hierarchical ZSM-5 zeolites (xHF-ZSM5) were obtained by chemical etching with fluoride ions and characterized by XRD, FTIR, NH₃-TPD, SEM, TEM, N₂ adsorption-desorption. They showed higher BET surface area, larger mesoporous volume, less defect zones, commensurable microporous structure and acid property compared with that of the parent ZSM-5. The defects were dissolved resulting in higher crystallinity zeolite. They showed better catalytic performance with less carbon deposition in catalytic cracking of n-hexane due to superior channel structure, large mesoporous and macroporous structure. In order to reduce the amount of carbon deposition further, 0.5HF-ZSM5 was selected and made phosphorus modification. After phosphorus modification, the catalytic activity and stability was maintained at a high level, and the carbon deposition of n-hexane cracking was restrained due to the gradual decreasing of acid amount with the increase of phosphorus content. The amount of carbon deposition decreased and reached the minimum of 23 mg g⁻¹ for 0.5HF-ZSM5-1P, which was four times less than that of the parent ZSM-5.