The Design And Application Of Novel Cr-based Catalysts For Non-oxidative Dehydrogenation Of Propane

With increasing demand for propene and other olefins,it is necessary to exploit the components of C3 and C4 hydrocarbons in the liquefied petroleum gas.The key to solving this problem is to develop a dehydrogenation catalyst with high activity,excellent stability and good selectivity.Nowadays,the industrialized catalysts for propane dehydrogenation are Pt-based and Cr-based catalysts.The Pt-based dehydrogenation catalyst possesses high activity and high selectivity,but the catalyst is costly.Besides,the presence of sulfur tends to poison Pt catalyst and cause the deactivation of catalyst.On the contrary,the chromia-based catalyst has a stronger sulfur tolerance as well as high activity and low cost,which have attracted extensive attention.However,chromia-based catalysts are easy to deactivate,needing frequent regeneration.In this case,developing a novel chromium catalyst with high activity,high selectivity and high stability can not only reduce the waste of resources but also can relieve the pressing propene supply-demand inbalance.In this paper,an impregnation method and a cation-anion double hydrolysis method were applied to synthesize chromium-based catalyst.The influence of impregnation sequence of K and Cr on the catalytic performance of chromium catalyst was investigated.A variety of characterization techniques were used to characterize the physicochemical properties of catalysts,followed by the evaluation of dehydrogenation performance of catalysts.The catalyst with K impregnated prior to Cr loading(sample Cr/K/Al2O3)exhibited higher propene selectivity than that prepared with the reverse impregnation sequence(sample K/Cr/Al2O3).Catalyst Cr/K/Al2O3 possesses more readily reducible chromium species compared with catalyst K/Cr/Al2O3.The majority of chromium species were observed to exist as polymeric species on catalyst Cr/K/Al2O3,while isolated and oligomeric chromium species were mainly found on catalyst K/Cr/Al2O3.A detailed correlation between catalytic performance and characterization results demonstrated that isolated and oligomeric species possessed higher cracking and coking activities than polymeric chromium species,which may account for the difference in the propene selectivity of catalysts.For the chromium catalyst with alumina as support,the dehydrogenation activity and selectivity of the catalyst was influenced mainly by changing the distribution of chromium species on the catalyst surface.Cation–anion double hydrolysis method was applied to synthesis composite oxide catalyst containing chromium.The effects of crystallization temperature,promoter Mg,template,pH,and time of crystallization were also investigated.The synthesis conditions were optimized.It is found that isolated and oligomeric chromium species are favored on the catalyst crystallized at lower temperatures,while the formation of crystalline Cr2O3 was promoted at higher temperatures.Besides,formate was the main intermediate formed during reaction on the catalysts crystallized at lower temperatures.