Article ID Journal Published Year Pages File Type
55618 Catalysis Today 2012 11 Pages PDF
Abstract

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.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (252 K)Download as PowerPoint slideHighlights► 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.

Related Topics
Physical Sciences and Engineering Chemical Engineering Catalysis
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