A facile and effective method for the distribution of Mo/HZSM-5 catalyst active centers

• Published in: Catalysis letters 2003-07, Vol.89 (1-2), p.75-79
• Main Authors: Wang, Hongxia, Hu, Gang, Hao Lei, Xu, Yide, Bao, Xinhe
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Catalysts: preparations and properties; Chemistry; Deactivation; Exact sciences and technology; General and physical chemistry; Ion-exchange; Methane; Molybdenum; NMR spectroscopy; Steaming; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; X ray photoelectron spectroscopy; Zeolites; Zeolites: preparations and properties
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1023/A:1024771410249

Post-steaming treatment of Mo/HZSM-5 catalysts results in more molybdenum species migrating into and residing in the HZSM-5 zeolite channels. This is confirmed by XRF and XPS measurements. 1H MAS NMR and 29Si MAS NMR also demonstrate that the number of free Brönsted acid sites decreases in the Mo/HZSM-5 catalysts that underwent post-steaming treatment, compared to untreated Mo/HZSM-5 catalysts. As a result, the deactivation rate constant (kd) on the Mo/HZSM-5 catalyst after post-steaming treatment for 0.5h is much smaller, and the catalyst therefore shows remarkable stability in the probe reaction of methane dehydro-aromatization. The results suggest that a more beneficial bi-functional balance between active Mo species for methane activation and acid sites for the following aromatization is developed over those Mo/HZSM-5 catalysts that have experienced post-steaming treatment for 0.5h, in comparison with the untreated Mo/HZSM-5 catalysts.