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  • 1
    Electronic Resource
    Electronic Resource
    An infrared spectroscopic study of the mechanism of chloromethane conversion to higher hydrocarbons on HZSM5 catalyst (1995)
    Springer
    Catalysis letters 33 (1995), S. 75-90 
    Details
    ISSN: 1572-879X
    Keywords: infrared spectroscopy ; chloromethane ; HZSM5 catalyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Investigation of the reaction mechanism of chloromethane on ZSM5 is a new topic. In this work an in situ FTIR technique was employed to study the conversion processes of chloromethane, the active sites on HZSM5, and the desorption state of surface species. The catalytic conversion of chloromethane to higher hydrocarbons was also studied. It is demonstrated that chloromethane can be reversibly adsorbed on acidic sites of HZSM5 at room temperature. At 100°C chloromethane is irreversibly and dissociatively adsorbed on the strong acidic sites of HZSM5, on which surface methoxyl is formed as proved by infrared characteristic C-H stretchings of-CH3 at 2960 and 2870 cm−1. Alkoxyls are produced and adsorbed on the catalyst surface as characterized by the infrared absorption bands of -CH2-groups at 1460 and 2930 cm−1. At 100°C the adsorbed methoxyl and alkoxyls are the main surface species, and a small amount of aromatics might exist as detected by a characteristic absorption band at 1510 cm−1. Between 100 and 200°C the adsorbed surface methoxyl and alkoxyls are converted to aromatics, and the occupied OH groups partially appear. At temperature higher than 300°C the adsorbed aromatics are thermally desorbed into the gas phase. Aromatics and alkanes are the main products in catalytic conversion. These results reveal that the formation of aromatics from methoxyl and alkoxyls is easier than the desorption of aromatics from HZSM5 catalyst. An alkoxyl mechanism is proposed for the conversion of chloromethane on HZSM5 based upon the experimental results and the three assumptions: (a) The primary C-C bond is formed from surface methoxyl groups via the methoxyl group polarization and C-H bond weakening, (b) The adsorbed alkoxyls are converted to aromatics via hydrogen transfer and bond rearrangement similar to the conventional carbenium ion mechanism for the aromatization of olefins and alkanes on HZSM5. The hydrogen atoms from the aromatization stimulate the desorption of alkoxyls to alkanes. (c) At temperature higher than 300°C surface reactions and desorption of adsorbed species take place simultaneously, determining the product distribution in the catalytic conversion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00817048
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  • 2
    Electronic Resource
    Electronic Resource
    Aromatization of methane in the absence of oxygen over Mo-based catalysts supported on different types of zeolites (1998)
    Springer
    Catalysis letters 56 (1998), S. 207-213 
    Details
    ISSN: 1572-879X
    Keywords: zeolite structure ; methane aromatization ; MoO3 ; benzene ; shape-selective function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic performance of Mo-based catalysts supported on various zeolites has been studied for methane aromatization in the absence of oxygen in a fixed-bed continuous-flow quartz reactor, and their catalytic properties are correlated with features of zeolite structure. It was found that H-type silica–alumina zeolites, such as ZSM-5, ZSM-8, ZSM-11 and β possessing two-dimensional structure and pore diameter equaling the dynamic diameter of a benzene molecule (about 6 Å) simultaneously, are fine supports for methane activation and aromatization catalysts. Among them, MoO3/H-ZSM-11 has the best activity and stability; for instance, a methane conversion of 8.0% and selectivity higher than 90% was obtained at 973 K. The catalytic performance of MoO3/H-ZSM-8 is somewhat lower than that of MoO3/H-ZSM-5, while activity of MoO3/H-β is lower than that of MoO3/H-ZSM-8. Catalysts supported on H-MCM-41 and H-SAPO-34 exhibit low activity for methane aromatization and those supported on H-MOR, H-X and H-Y give only a little amount of ethylene. Over MoO3/H-SAPO-5 and MoO3/H-SAPO-11 no hydrocarbons were detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019046104593
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    Paper (German National Licenses)
    Fulltext
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