Abstract
Highly active and heat‐resisting W/HZSM‐5‐based catalysts for nonoxidative dehydro‐aromatization of methane (DHAM) have been developed and studied. It was found from the experiments that the W−H2SO4/HZSM−5 catalyst prepared from a H2SO4‐acidified solution of ammonium tungstate (with a pH value at 2–3) displayed rather high DHAM activity at 973–1023 K, whereas the W/HZSM‐5 catalyst prepared from an alkaline or neutral solution of (NH4)2WO4 showed very little DHAM activity at the same temperatures. Laser Raman spectra provided evidence for existence of (WO6)n- groups constructing polytungstate ions in the acidified solution of ammonium tungstate. The H2‐TPR results showed that the reduction of precursor of the 3% W–H2SO4/HZSM‐5 catalyst may occur at temperatures below 900 K, producing W species with mixed valence states, W5+ and W4+, whereas the reduction of the 3% W/HZSM‐5 occurred mainly at temperatures above 1023 K, producing only one type of dominant W species, W5+. The results seem to imply that the observed high DHAM activity on the W–H2SO4/HZSM‐5 catalyst was closely correlated with (WO6)n- groups with octahedral coordination as the precursor of catalytically active species. Incorporation of Zn (or La) into the W–H2SO4/HZSM‐5 catalyst has been found to pronouncedly improve the activity and stability of the catalyst for DHAM reaction. Over a 2.5% W–1.5% Zn–H2SO4/HZSM‐5 catalyst and under reaction conditions of 1123 K, 0.1 MPa, and GHSV=1500 ml/(h g−cat.), methane conversion (XCH4) reached 23% with the selectivity to benzene at ∼96% and an amount of coke for 3 h of operation at 0.02% of the catalyst weight used.
Similar content being viewed by others
References
O.V. Bragin, T.V. Vasina, A.V. Preobrazhenskii and K.M. Minachev, Izv. Akad. Nauk SSSR, Ser. Khim. (1982) 954; (1989) 750.
T. Koerts, M.J.A.G. Deelen and R.A. van Santen, J. Catal. 138 (1992) 101.
L. Wang, L. Tao, M. Xie, G. Xu, J. Huang and Y. Xu, Catal. Lett. 21 (1993) 35.
D.J. Wang, J.H. Lunsford and M.P. Rosynek, J. Catal. 169 (1997) 347.
F. Solymosi, A. Erdohelyi and A. Szoke, Catal. Lett. 32 (1995) 43.
F. Solymosi, J. Cserenyi, A. Szoke, T. Bansagi and A. Oszko, J. Catal. 165 (1997) 150.
F. Solymosi, A. Szoke and J. Cserenyi, Catal. Lett. 39 (1996) 157.
S. Wong, Y. Xu, L. Wang, S. Liu, G. Li, M. Xie and X. Guo, Catal. Lett. 38 (1996) 39.
L. Chen, L. Lin, Z. Xu, T. Zhang and X. Li, Catal. Lett. 39 (1996) 169.
Y. Shu, Y. Xu, S. Wang, L. Wang and X. Guo, J. Catal. 170 (1997) 11.
S. Liu, Q. Dong, R. Ohnishi and M. Ichikawa, Chem. Commun. (1997) 1455.
J.L. Zeng, Z.T. Xiong, G.D. Lin, H.B. Zhang and K.R. Tsai, in: 11th ICC, Baltimore, 1996, Po-158; J. Xiamen Univ. 35 (1996) 900.
A.F. Well, Structural Inorganic Chemistry, 5th Ed. (Clarendon Press, Oxford, 1984) p. 519, and references therein.
N. Weinstock, H. Schulze and A. Muller, J. Chem. Phys. 59 (1973) 5063.
Landolt-Bornstein, Physikalisch-Chemische Tabellen, Vol. 2 (1951).
H. Knozinger and H. Jeziorwski, J. Phys. Chem. 82 (1978) 2002; 83 (1979) 1166.
J.L. Zeng, Z.T. Xiong, L.J. Yu, G.D. Lin and H.B. Zhang, J. Xiamen Univ. 37 (1998), in press.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Zeng, J., Xiong, Z., Zhang, H. et al. Nonoxidative dehydrogenation and aromatization of methane over W/HZSM‐5‐based catalysts. Catalysis Letters 53, 119–124 (1998). https://doi.org/10.1023/A:1019033201075
Issue Date:
DOI: https://doi.org/10.1023/A:1019033201075