Methane Dehydroaromatization Reaction on Mo-based Catalyst: Effect of
the Catalyst Acidity and Porosity
| Dr. Lingling Su(1999-2003) |
Directed by Prof. Xinhe Bao and Yide Xu |
| Abstract | Present address: Japan |
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Methane
dehydroaromatization (MDA) under nonoxidative condition is one of the
important reactions in the field of direct conversion of methane. It is
of significance for both the utilization of natural gas and the understanding
of the nature of C-H bond activation in methane molecule. In this dissertation
the effect of the zeolite acidity and porosity on the catalytic performance
of MDA on Mo-based catalysts is investigated. The number of the Bronsted
acid sites and the value of Mo/[H+] per unit cell on the Mo/HZSM- |
5 catalysts with different ratios of SiO2/Al2O3
and the Mo/HZSM-5 catalysts with different Mo loadings are measured
by the 1H MAS NMR experiments.
From the
results it is concluded that the migration ability of Mo species into
the zeolite channels strongly depends on the number of the Bronsted
acid sites per unit cell. The in situ 1H MAS NMR experiments
also demonstrate that the Bronsted aicd sites, once replaced and occupied
by Mo species, can not regenerate during the induction period of the
reaction. Combining the 1H MAS NMR results with the reaction results
we find that the Mo/HZSM-5 catalyst with the value of Mo/[H+]
close to 1.0 shows the best catalytic performance of MDA reaction. The
cooperated function of the Mo species with the Bronsted acid sites is
the basis of the MDA reaction.
The catalyst porosity can be modified by alkali treatment. Under an appropriate condition of the alkali treatment the micropore structure of the HZSM-5 and MCM-22 zeolites is not affected obviously, but some new mesopores can be developed.
The Mo based catalyst derived from the appropriate alkali treated zeolite exhibits good catalytic performance due to the coexistence of micropores and mesopores, which is beneficial to the mass transfers of the aromatic product formed during the MDA reaction, thus increasing the reaction stability.The effect of synthesis condition of the HZSM-5 zeolite on the MDA reaction performance is also investigated. The catalytic performance of MDA on a Mo/HZSM-5 catalyst derived from the HZSM-5 zeolite prepared from soluble glass is better than that derived from the HZSM-5 zeolite prepared from silicon gel.
The catalyst porosity can be modified by alkali treatment. Under an appropriate condition of the alkali treatment the micropore structure of the HZSM-5 and MCM-22 zeolites is not affected obviously, but some new mesopores can be developed.
The Mo based catalyst derived from the appropriate alkali treated zeolite exhibits good catalytic performance due to the coexistence of micropores and mesopores, which is beneficial to the mass transfers of the aromatic product formed during the MDA reaction, thus increasing the reaction stability.The effect of synthesis condition of the HZSM-5 zeolite on the MDA reaction performance is also investigated. The catalytic performance of MDA on a Mo/HZSM-5 catalyst derived from the HZSM-5 zeolite prepared from soluble glass is better than that derived from the HZSM-5 zeolite prepared from silicon gel.
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The methane conversion and the yield of aromatics
as a function of Mo/[H+] ratio (Si/Al
ratios and metal loadings) |