Bifunctional catalysis of Mo/HZSM-5 in the dehydroaromatization of methane to benzene and naphthalene XAFS/TG/DTA/MASS/FTIR characterization and supporting effects
- Hakkaido Univ., Sapporo (Japan). Catalysis Research Center
The direct conversion of methane to aromatics such as benzene and naphthalene has been studied on a series of Mo-supported catalysts using HZSM-5, FSM-16, mordenite, USY, SiO{sub 2}, and Al{sub 2}O{sub 3} as the supporting materials. Among all the supports used, the HZSM-5-supported Mo catalysts exhibit the highest yield of aromatic products, achieving over 70% total selectivity of the hydrocarbons on a carbon basis at 5--12% methane conversion of 973 K and 1 atm. By contrast, less than 20% of the converted methane is transformed to hydrocarbon products on the other Mo-supported catalysts, which are drastically deactivated, owing to serious coke formation. The XANES/EXAFS and TG/DTA/mass studies reveal that the zeolite-supported Mo oxide is endothermally converted with methane around 955 K to molybdenum carbide (Mo{sub 2}C) cluster (Mo-C, C.N. = 1, R = 2.09 {angstrom}; Mo-Mo, C.N. = 2.3--3.5; R = 2.98 {angstrom}), which initiates the methane aromatization yielding benzene and naphthalene at 873--1023 K. Although both Mo{sub 2}C and HZSM-5 support alone have a very low activity for the reaction, physically mixed hybrid catalysts consisting of 3 wt% Mo/SiO{sub 2} + HZSM-5 and Mo{sub 2}C + HZSM-5 exhibited a remarkable promotion to enhance the yields of benzene and naphthalene over 100--300 times more than either component alone. The bifunctional catalysis of Mo/HZSM for methane conversion towards aromatics is discussed by analogy with the promotion mechanism on the Pt/Al{sub 2}O{sub 3} catalyst for the dehydro-aromatization of alkanes.
- OSTI ID:
- 316343
- Journal Information:
- Journal of Catalysis, Vol. 181, Issue 2; Other Information: PBD: 25 Jan 1999
- Country of Publication:
- United States
- Language:
- English
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