Hydrogenation Ability of ZSM-5 Zeolite.

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  • ZSM-5ゼオライトの水素化能

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Hydrogenation of ethylene and propylene was carried out over the protonated ZSM-5 (HZSM-5) and the alkaline earth metal-containing ZSM-5 type zeolites (M-HZSM-5, M: alkaline earth metal). Products, both of low and high molecular weights, were formed through a variety of reactions such as polymerization, isomerization, cracking, and hydrogenation. The lower molecular weight hydrocarbons produced over the HZSM-5 were mainly paraffins. The yields of light olefins were dependent on the kinds of zeolite used and increased in the following order: HZSM-5_??_Mg-HZSM-5<Ca-HZSM-5<Sr-HZSM-5<Ba-HZSM-5. Hydroconversion of benzene was also carried out over these zeolites. The catalytic activity of M-HZSM-5 was lower than that of HZSM-5. In the case of M-HZSM-5, the hydrogenated product, cyclohexane, and its skeleton isomer, methylcyclopentane, were detected in the reaction products at about 300°C. In order to clarify the essential sites for the hydrogenation, effects of impurities, especially iron, contained in the zeolites as hydrogenation catalysts, were studied in detail. It was found that the HZSM-5 zeolite, which does not contain iron at all, showed a significant hydrogenation activity. From these results, we have concluded that the active sites for the hydrogenation of ethylenic double bonds are the strong acid sites of the HZSM-5 zeolite, and that the hydrogenation activity decreases upon the modification of the zeolite with alkaline earth metals.

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