Mild-acid-assisted thermal or hydrothermal dealumination of zeolite beta, its regulation to Al distribution and catalytic cracking performance to hydrocarbons

• Published in: Journal of catalysis Vol. 362; pp. 94 - 105
• Main Authors: Wang, Wennian, Zhang, Wei, Chen, Yunlei, Wen, Xiaodong, Li, Hao, Yuan, Delin, Guo, Qiaoxia, Ren, Shenyong, Pang, Xinmei, Shen, Baojian
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-06-2018
• Subjects: Acidity; Al distribution; Catalytic cracking; Dealumination; Zeolite beta; Zeolite beta; Al distribution; Dealumination; Acidity; Catalytic cracking
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2018.03.002

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•Dilute HCl combined with steaming or calcination removed ∼70% Al of zeolite β.•Combined dealumination was more versatile than single treatment.•Acid steaming removed Al on T2, T5, T6, and T7 sites and drove poly-EFAL to external surface.•Acid calcination resulted in a more homogeneous Al distribution in zeolite β structure.•Acid calcination caused stronger B acidity and higher B acid density than acid steaming.
The synthesized nanoscale beta zeolites (SiO2/Al2O3 = 25, nanocrystals of 50 nm) were treated by two different sequential procedures called acid-steaming and acid-calcination treatment: that is, dilute HCl aq. solution (less than 1 mol/L) treatment followed by either steaming or calcination. These successive treatments were applied two times. The effect of both acid-steaming and acid-calcination treatment of beta zeolite on framework Al at different T-sites, extra-framework Al (EFAL) of different types, and acidity was studied. It was found that nearly 70% of Al was removed in these processes, the location and state of Al in zeolite beta are regulated by different combinations of treatments. 27Al (MQ) MAS NMR, IR, XPS, and XRF data showed that steaming dominated dealumination in the acid-steaming treatment, and Al atoms on T2, T5, T6, and T7 sites were almost completely removed. More EFAL species were formed and migrated to external surfaces of zeolite beta. In acid-calcination treatment, dealumination was completed stepwise by calcination and acid treatment, framework Al atoms on T5, T6, and T9 sites were removed, and more monomeric EFAL species were formed, leading to a more homogeneous Al distribution. The resultant zeolites beta treated by acid calcination and by acid steaming show similar bulk SiO2/Al2O3 ratios but different acidity distributions. Acid-calcination treatment results in more Brønsted acid sites and stronger Brønsted acidity than acid-steaming treatment, leading to higher conversion in n-octane catalytic cracking and higher gasoline yield in vacuum gas oil catalytic cracking.