Prepared Cr-based Catalyst For Dehydrogenation Of Propane To Propene And Its Catalytic Activity

In recent years, the propylene is an important petrochemical intermediates. Thecatalytic dehydrogenation of propane to propene is of increasing importance, due tothe growing demand for propene, which is important resource in the production ofpolypropene, polyacryonitrile, acrylic acid. Propane is low cost and abundant naturalresources in our country, it is a great significant thing to convert the low value of propaneinto high value propylene. Therefore, much attention has been paid to developthe dehydrogenation catalyst of proane to propylene. The reaction of dehydrogenation ofpropane is an endothermic reaction, so relatively high reaction temperatures areneeded to obtain high yield of propylene. The high reaction temperatures favorthermal cracking reactions to form alkanes and alkenes, leading to decreasing productyield and increasing catalyst deactivation. Oxidative dehydrogenation of propane byoxygen is an attractive, because it is an exothermic and nonthermodynamicallylimited reaction. Propane could dehydrogenate to propylene at low temperatures, and at thesame time, it also could slow the rate of carbon depositing catalyst surface. Therefore, it is achallenging research topic to obtain higher propane conversion and higher propyleneselectivity at the same time in the reaction of propane dehydrogenation. Recent years,chromium，vanadium and precious metals platinum are chosen as the active components forthe catalysts for propane dehydrogenation. In addition, the preparation method of catalysteffects the performance of catalyst. Based on the above analysis, this thesis take differentapproaches to prepare different catalysts, and study those catalytic properties. Thestudy includes the following aspects:1. catalysts of Cr/Al203been synthesized via precipitation method by using a surfactantof cetyltrimethylaminonium bromide(CTAB). According to the activity of catalyst, thosecatalysts have good catalytic performance,9.5Cr/Al2O3catalysts had the highest catalyticperformance. Under optimum conditions, the initial conversion of propane and selectivity ofpropylene were as high as65%and90%, respectively. After deactivation due to coking,catalysts could be regenerated by regeneration. No obvious decreasing of catalytic activity isnoticed after3times reuse. 2.A series of catalysts were prepared by hydrothermal synthesis using(etrapropylammonium hydroxide as structure-directing agent. According to the activity ofcatalyst, those catalysts have good catalytic performance,7.5Cr/Al203catalysts hadthe highest catalytic performance. After deactivation due to coking, catalysts could beregenerated by regeration.3.Catalysts were prepared in ethanol solvent by solvothertnal process using the samesteps, According to the activity of catalyst, Cr/Al-5.0catalysts had the highest catalyticperformance. Compared with other two methods, those catalysts withthe low chrome content (5wt.%) provides very high activity performance.4. Catalysts were analysised by the UV-vis and XPS, trivalent chromium andhexavalent chromium exist in th6e catalysts. Cr+species are beneifcial to improving theactivity of the catalyst，6and the ratio of Cr7C3r+are closely related to the activity of thecatalyst.