Modification of the Acidic and Textural Properties of HY Zeolite by AHFS Treatment and Its Coke Formation Performance in the Catalytic Cracking Reaction of N-Butene

Coke formation on n-butene cracking catalyst is the main reason for the reducing of its lifetime. To study the effects of acidity and textural properties on the coke formation process, a series of HY zeolite-type catalysts were prepared by ammonium hexafluorosilicate treatment (AHFS). NH3-TPD and Py-IR-TPD were used to systematically study the change law of zeolite acidity. It was found that with the increase of AHFS concentration, the acid density decreased, whereas the ratio of Bronsted acid to Lewis acid first increased and then decreased. Meanwhile, the percentage of Bronsted acid inside the supper cages increased and the strength of Bronsted acid increased with the degree of dealumination. Combined with in situ IR study on coke formation, the relationship between coking and acid site was revealed. It was found that the rate of coke formation on zeolites was affected by acid density, which is the rate of coke formation decreased with the decline of acid density. When the acid density remains at the same level, it was the acid strength that determined the coke formation rate-the stronger the acid strength, the faster the coke formation rate.