With incorporation of Ga3+/Zn2+ (or Co3+/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% similar to 72% selectivity to benzene formation at similar to 15% conversion of CH4 could be achieved in the initial similar to 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 (less than or equal to 1.2%) or H-2 (similar to 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 Co3+/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-strung acid sites, mostly B-acid sites, simultaneously. The latter could serve as the catalytically active sites for DRAM 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 Co3+/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 H-2-TPR study. The above two roles that Ga3+/Zn2+ (or Co3+/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.
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