Abstract
The active site requirements for methane dehydroaromatization by Mo/HZSM-5 were investigated by employing as catalysts physical mixtures of Mo-bearing supports (HZSM-5, SiO2, γ-Al2O3, and activated carbon) and HZSM-5. Separation of the two catalyst components after activation or reaction was possible by using two different sieve fractions. Our comparison demonstrates that migration of volatile Mo oxides into the micropores of HZSM-5 is at the origin of the observed catalytic synergy in methane dehydroaromatization for physical mixtures. The propensity of Mo migration depends on the activation method and the Mo–support interaction. Migration is most pronounced for Mo/SiO2. Prolonged exposure of HZSM-5 zeolite to Mo oxide vapors results in partial destruction of the zeolite framework. Mo carbide dispersed on nonzeolitic supports afforded predominantly coke with only very small amounts of benzene. The main function of the zeolite is to provide a shape-selective environment for the conversion of methane to be...
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