关键词: 甲烷, 脱氢芳构化, W/MCM-22, W-Zn-Ga/MCM-22, W-Mo-Co/MCM-22

With incorporation of Ga³⁺/Zn²⁺ (or Co^3+/2+/Moⁿ⁺) into a W/MCM-22 host catalyst, highly active and heat-resistant doubly promoted W/MCM-22-based catalysts for dehydro-aromatization of methane (abbreviated as DHAM) were prepared. Over an 8% W-0.1% Co-0.4% Mo/MCM-22 or 8% W-0.1% Ga-0.6% Zn/MCM-22 catalyst, 70%～72% selectivity to benzene formation at ～15% conversion of CH₄ could be achieved in the initial ～3 h of reaction under reaction condition of 0.1 MPa, 1073 K, GHSV=1500 mL(STP)·h^-1·(g-cat.)^-1. Addition of a proper amount of CO₂(≤1.2%) or H₂(～7.0%) to the feed-gas was found to significantly enhance conversion of CH₄ and selectivity to benzene, and to improve the performance of coke-resistance of the catalysts. By correlating the results of the NH₃-TPD measurements and the catalyst tests, it was confirmed that intensity and concentration of the surface B-acid sites have pronounced effects on the performance of the catalyst for DHAM reaction. It was found experimentally that addition of a proper amount of Ga³⁺/Zn²⁺ (or Co^3+/2+/Moⁿ⁺) into W/MCM-22 host catalyst resulted not only in eliminating parts of the strong surface B-acid sites but also in generating a kind of new medium-strong acid sites, mostly B-acid sites, simultaneously. The latter could serve as the catalytically active sites for DHAM reaction, and on such medium-strong surface B-acid sites, the formation of coke would be also alleviated to a greater extent. On the other hand, the doping of the Ga³⁺/Zn²⁺ (or Co^3+/2+/Moⁿ⁺)-components to tungsten oxide matrix would facilitate inhibiting aggregation of the W-containing active species and improving dispersion of the W-component at the surface of catalyst, thus leading to a pronounced decrease in the reduction-temperature for the hard-to-be-reduced W⁶⁺-species and an increase in quantity of the reducible W⁶⁺-species, as evidenced by the results of the H₂-TPR study. The above two roles that Ga³⁺/Zn²⁺ (or Co^3+/2+/Moⁿ⁺) as promoters played were contributed to the high CH₄ conversion and benzene selectivity, the alleviation of coke deposition and the improvement of the durability of the catalyst.

Key words: methane, dehydro-aromatization, W/MCM222,W-Zn-Ga/MCM-22, W-Mo-Co/MCM-22