Study On The Benzene Selective Hydrogenation Over Rur Catalyst Supported On The Mesoporous Molecular Sieve

Cyclohexene is a useful chemical widely used in organic chemical industry, fine chemicalindustry, and so on. Owing to the atomically economy, partial hydrogenation of benzene tocyclohexene has recently been the focus of much attention. And, to date, the only industrializedcatalyst for cyclohexene via partial hydrogenation of benzene just employed the unsupportedRu-Zn catalyst developed by Asahi Chemical Industry Co. However, the catalytic efficiency interms of the utilization per unit mass of Ru was low, the catalyst had poor resistance to S, As, Pb,and was costly. In contrast, supported catalyst not only can contral the catalyst's activity andselectivity, but also effectively enhance it's efficiency and life cycle. So, we have an observe andstudy in the benzene selective hydrogenation reaction employ Ru catalyst supported on themesoporous molecular sieve, furthermore, we study the effect of promoter's kinds or content tothe catalyst.Firstly, we prepared Ru catalyst supported MCM-41 by incipient impregnation and studiedit's performance in benzene selective hydrogenation. When the Ru content is 1 wt%, in certainconditions, the benzene conversion is 40.3 % and the cyclohexene selectivity up to 37.7 %.When ZnCl₂ or Zn(CH₃COO)₂ were used as zinc precursor, Ru was easily to be reduced andresulted in the increase of the number of active centers on the catalyst surface, and so the catalystshowed higher activity.. When Zn(NO₃)₂ was used as zinc precursor, part of Ru was difficult tobe reduced, so the activity was lowered down. The use of ZnSO₄ made the surface of the catalystshowing acidity. When it was used for selective hydrogenation, there were two routes forbenzene hydrogenation. So, the reaction rate and benzene conversion increased. Furthermore, theexisting of acid sites was in favor of the adsorption of cyclohexene, thereby it wasover-hydrogenated easily and cyclohexane was the main product.Secondly, we studied the effect of Zn content to Ru/MCM-41's performance. And we foundthat benzene conversion and cyclohenxne selectivity decreased seriously with the Zn contentincreased, we concluded that Zn promoter make two kinds of hydrogenation sites on the catalysts.The weak hydrogenation sites about 2⁴ nm can promote benzene conversion, and the 50⁸0 nmmoderately strong hydrogenation sites, a novel kind of hydrogenation site found on the surfaceof the catalysts under the influence of Zn, are beneficial for cyclohexene hydrogenation. When the Zn contents increase, the numbers of moderately strong hydrogenation sites is more than theweak hydrogenation sites, so bring about the above phenomenons.Lastly, we prepared Ru catalyst supported SBA-15 by incipient impregnation and studiedit's performance in benzene selective hydrogenation, When reaction 30 min at 403 K, thebenzene conversion is 70.7 % and the cyclohexene selectivity is 28.0 % on 4 wt%Ru/SBA-15.And we found that benzene conversion increased and cyclohenxne selectivity decreased with theZn promoter added. Which is different from other references. By characteristic the catalyst inXRD, TEM and TPR, We found that Zn promoter can make Ru to be reduced easily and increasethe number of active centers on the catalyst surface.