Improving effect of Fe additive on the catalytic stability of Mo/HZSM-5 in the methane dehydroaromatization

• Published in: Catalysis today Vol. 185; no. 1; pp. 41 - 46
• Main Authors: Xu, Yuebing, Wang, Jide, Suzuki, Yoshizo, Zhang, Zhan-Guo
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 20.05.2012; Elsevier
• Subjects: additives; Carbon nanotube; carbon nanotubes; Catalysis; catalysts; catalytic activity; Chemistry; Exact sciences and technology; General and physical chemistry; Ion-exchange; Metal additives; methane; Methane dehydroaromatization; Mo/HZSM-5; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites: preparations and properties; Carbon nanotube; Methane dehydroaromatization; Mo/HZSM-5; Metal additives; Methane; Scanning electron microscopy; Catalytic reaction; Stability; Coke; Screen; Carbon nanotubes; Modified catalyst; Transition metal; Mechanism; Heterogeneous catalysis; Additive
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2011.09.026

Fe promoter improves significantly the catalytic stability of Mo/HZSM-5 in the non-oxidative dehydroaromatization at severe condition. [Display omitted] ► Screening of transition metal promoters at the severe condition of 1073K and 10,000mL/g/h. ► Long term periodic CH4–H2 switch tests to confirm Fe's promotional effect. ► SEM observation and TPO, TG and BET measurements to study the promotion mechanism. ► Formation of Fe-induced carbon nanotubes and Fe-catalyzed coke removal are related to the promotional effect. The promotional effects of eight kinds of transition metal additives (0.5wt%) on the activity and stability of 5wt%Mo/HZSM-5 were screened at 1073K and 10,000mL/g/h in a continuous CH4 feed mode. Only Fe was observed to improve the activity stability. Subsequently, confirmation tests were performed with other three Fe-modified catalysts containing 0.3, 1.0 and 2.0wt% of Fe in the same continuous operation mode and also with the 0.5wt%Fe–5wt%Mo/HZSM-5 under periodic CH4–H2 switch operation for 1650min. It was confirmed that Fe indeed enhanced the stability of Mo/HZSM-5 catalyst. Then, TPO, TG and BET measurements and SEM observations were performed for almost all spent samples to gain insight into the promotion mechanism of Fe additive. The results revealed that over short time frames in the continuous CH4 feed mode the formation of Fe-induced carbon nanotubes is the origin of its promotional effect, while under the long-term periodic CH4–H2 switch operation the catalytic involvement of Fe in the surface coke removal during the H2 flow periods is the main cause of Fe-modified catalyst being much more stable than the unmodified Mo/HZSM-5 catalyst