Propane Dehydrogenation Over Cr-based And Zn-based Catalysts Synthesized By Aerosol-assisted Method

Propene is an important raw material in petrochemical industry. It is usually supplied by conventional craking processes (e.g., FCC and steam craking). But the crude oil is now in short supply due to the huge consumption in the world, and the craking process cannot catch up with the demand of the market. Since propane resource is rich in China, dehydrogenation of propane (DHP) is one of the most promising propene production technology. As the active compositions, chromium-based and platinum-based catalysts have been widely investigated as the DHP catalysts. As comparison to Pt-based catalysts, Cr-based catalysts is much cheaper. However, Cr-based catalysts, which are prepared by impregnation method, is severely polluted to the environment.Despite a great deal of research, the loading of the best chromium-based catalyst is still high. Therefore the goal is to prepare chromium-based catalyst with low loading or change the active metal compositions.In this study the chromium-based and zinc-based catalysts synthesized by aerosol-assisted method were investigated for dehydrogenation (DHP) of propane. The catalysts were characterized by XRD, UV-vis, Raman, SEM, TEM and N2 adsorption-desorption techniques.The pore structure of Cr-based catalyst is the mixture of hexagonal and worm like channels. Propane conversion, propene selectivity and yield reach a maxinum under the reaction condition of 580℃ and 20ML/min. Besides, when the chromium oxide loading is low, the surface species mainly include tetrahedral monochromate and dichromatete. The six-coordinated α-Cr2O3 phase appears as the Cr2O3 loading increases. The catalytic performance 3% Cr-based catalyst is the best. This is due to the tetrahedral Cr6+ is the active sites and α-Cr2O3 phase is harmful to the reaction.The study on the synthesis conditions of Zn-based catalysts showed that, the crystallinity of the zeolite has not been affacted by the crystallization temperature, but increases with increasing nTPAOH/nSi ratio. The zeolite synthesized with nTPAOH/nSi=0.06 already shows high crystallinity. Reaction result of propane dehydrogenation showed that the best reaction condition is reaction temperature 580℃ and flow rate 15-20ML/min. The best zinc oxide loading is between 5% and 7%. The active sites are framework zinc and small zinc oxide cluster. Its deactivition is mainly owing to the loss of zinc. The surface zinc species were changed during the regeneration of Zn-based catalysts. Large zinc oxide clusters appeared when the catalysts reacted with oxygen, which is proved to be disadvantageous to propane dehydrogenation.