Influence of the calcination treatment on the catalytic properties of hierarchical ZSM-5

• Published in: Catalysis today 2012-01, Vol.179 (1), p.91-101
• Main Authors: Serrano, D.P., García, R.A., Linares, M., Gil, B.
• Format: Article
• Language: English
• Subjects: acylation; air; aluminum; Calcination procedure; Catalysis; catalytic activity; Chemistry; crystallization; Epoxide rearrangement; epoxides; Exact sciences and technology; Friedel–Crafts acylation; General and physical chemistry; Hierarchical ZSM-5 zeolite; Ion-exchange; nitrogen; surface area; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; zeolites; Zeolites: preparations and properties
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2011.06.029

[Display omitted] ► Additional porosity in hierarchical ZSM-5 zeolite increases the accessibility to the active sites. ► The acidic properties of hierarchical ZSM-5 are very sensitive to the calcination conditions. ► Two-step nitrogen/air treatment allows a stronger Brønsted acidity and to be preserved, leading to improved catalytic activity. The effect of the calcination conditions on the properties and catalytic performance of hierarchical ZSM-5 zeolite has been investigated using different reactions as catalytic tests: acylation of aromatic substrates and rearrangement of linear and cyclic epoxides. The hierarchical h-ZSM-5 material was prepared by crystallization of silanized protozeolitic units. The removal of the organics present in the as-synthesized ZSM-5 samples has been carried out using two different calcination procedures: (i) directly under air atmosphere; (ii) following a two-step (nitrogen-air) treatment. Clear differences are noticed related to the textural properties of the ZSM-5 samples, since the h-ZSM-5 presents higher BET and external surface area than standard ZSM-5 zeolite. Whereas the calcination method does not affect the properties of the reference ZSM-5 sample, noticeable changes were observed over the hierarchical zeolite. The concentration of Brønsted acid sites decreases by half for one-step air calcination, but only a quarter when using a two-step nitrogen/air calcination, showing that the aluminium present in hierarchical ZSM-5 is very sensitive to the calcination conditions as it may undergo framework extraction and dehydroxylation phenomena. For all the studied reactions, the hierarchical sample, calcined by a two-step treatment, presents higher activity than when using direct air calcination.