Structure–deactivation relationship for ZSM-5 catalysts governed by framework defects

• Published in: Journal of catalysis Vol. 280; no. 2; pp. 196 - 205
• Main Authors: Barbera, Katia, Bonino, Francesca, Bordiga, Silvia, Janssens, Ton V.W., Beato, Pablo
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 13-06-2011; Elsevier; Elsevier BV
• Subjects: adsorption; Catalysis; Catalysts; Chemistry; crystals; Deactivation; Defects; Exact sciences and technology; gasoline; General and physical chemistry; H-ZSM-5; Hydrocarbons; Ion-exchange; Methanol; Methanol to hydrocarbons; pyridines; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites; Zeolites: preparations and properties; H-ZSM-5; Deactivation; Zeolites; Methanol to hydrocarbons; Defects; Hydrocarbon; Nitrogen heterocycle; Acidic site; Crystals; Alcohol; Conversion; Density; Physical properties; Heterogeneous catalysis; Pyridine; Synthesis; Adsorption; Six membered ring; Gasoline; Alkanol; Defect; Structure; Catalyst; Methanol
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2011.03.016

Internal framework defects are crucial for the deactivation behaviour of the ZSM-5 catalysts in the conversion of methanol to hydrocarbons. While the activity is related to the acid site density, the deactivation rate correlates with the measured intensity ratio of the IR bands for internal silanols at 3726 cm
−1 and for external silanol groups at 3745 cm
−1 (I
3726/I
3745).
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► The activity of H-ZSM-5 in the conversion of methanol to hydrocarbons is related to the Brønsted acid site density. ► Internal framework defects are crucial for the deactivation behavior of the ZSM-5 catalysts. ► The activity and deactivation of the H-ZSM-5 can be varied independently.
Zeolites are well known catalysts for the conversion of methanol to hydrocarbons. By adjusting the synthesis procedure, the activity and deactivation of the ZSM-5 zeolite in the conversion of methanol to gasoline can be varied significantly. We found that internal framework defects are crucial for the deactivation behavior of the ZSM-5 catalysts. Adsorption of pyridine and 2,4,6-collidine shows that the infrared band at 3745
cm
−1 can be assigned to isolated silanol groups on the external surface and the bands at 3726 and 3700
cm
−1 to silanol groups inside the zeolite crystals. While the activity is related to the acid site density, the deactivation rate correlates with the measured intensity ratio of the IR bands for internal silanols at 3726
cm
−1 and for external silanol groups at 3745
cm
−1 (I
3726/I
3745). The activity and deactivation, therefore, depend on a different physical property, which means that they can be varied independently.