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Steaming Drived Chemical Interactions of ZnClx with Y Zeolite Framework, Its Regulation to Dealumination/Silicon-Healing as well as Enhanced Availability of Brønsted Acidity

Peng Liu,Zhi Li,Xingyu Liu,Weiyu Song,Bowen Peng,Xinyue Zhang,Suofu Nie,Penghui Zeng,Zhongdong Zhang,Xionghou Gao,Baojian Shen

In fluid catalytic cracking (FCC), Brønsted acid plays a very important role. Herein, a zinc-modified ultrastable Y (USY) zeolite containing higher Brønsted acidity was prepared by synergistic treatment with zinc chloride and steaming. The results of characterization showed that selective dealumination and silicon healing due to introduction of zinc ions ([ZnCl]+ and [ZnOH]+) into zeolite could promote the formation of extra-framework silicon (EFS) and different silicon healing of the Al vacancies, which led to the formation of half-sodalite cages connecting with supercages and thus increased the availability of acidic sites in the sodalite cage. Meanwhile, DFT calculations demonstrated that the acidic strength of protons in the sodalite cage was enhanced by [ZnCl]+ and [ZnOH]+, and the synergy of Brønsted/[ZnCl]+ became stronger. As a result, the strong Brønsted acid was increased by 19%. This translated to higher n-octane and heavy oil (VGO) catalytic cracking activity and gasoline yield.