Study On Catalytic Performance Of NMO_x·ZSM-5 In N-Hexane Isomerization

A series of nMnO_x·ZSM-5,nNiMoO_x·ZSM-5 and nMoO_x/NiO_x·ZSM-5 catalysts were prepared by isometric impregnation method,and characterized by XRD,NH₃-TPD,BET techniques.The isomerization performance of catalysts was evaluated by using the n-hexane as model reactant in a high-pressure-micro-reactor.The results show that the diffraction peak of ZSM-5 is preserved well,and the crystalline peak of Mn,Mo and Ni oxides are not found,which indicate that the active components in the catalysts are highly dispersed.With the increasing of active component Mn content,part of acid sites of ZSM-5 are covered by Mn,which cause the total acid and the surface area of nMnO_x·ZSM-5 catalysts decrease.With the increasing of Ni/Mo atomic ratio,the total acid and strong acid sites of nNiMoO_x·ZSM-5 catalyst obviously increases,because of the adsorption,complexation and polarization of Ni to ammonia,the surface area of nNiMoO_x·ZSM-5 catalyst increase firstly and then decrease because of Ni²⁺incorporate into the ZSM-5 channel,which would replace part of H⁺,so that the cell volume and surface area increase.With the increasing of Mo content,Ni²⁺enter into the ZSM-5 channels,and cover part of acid sites of ZSM-5,which cause the total acid and strong acid sites of nMoO_x/NiO_x·ZSM-5 catalyst decrease.The isomerization performance of n-hexane results show that the conversion and selectivity of n-hexane isomerization of nMnO_x·ZSM-5catalyst decrease,with the increase of active component Mn content and activation temperature.The conversion and selectivity of 550-0.5%nMnO_x·ZSM-5 catalyst are 59.50%and 33.71%at 240?reaction temperature,but the conversion and selectivity of 550-7%catalyst decrease by 13.87%,8.10%,respectively.Compared with 550-0.5%nMnO_x·ZSM-5 catalyst,the conversion and selectivity of 650-0.5%catalyst decrease by 10.35%and 3.07%.The conversion and selectivity of 550-1 nNiMoO_x·ZSM-5 catalyst are 84.05%and 33.63%,increase by20.22%and 3.38%,compared with 550-0.3 nNiMoO_x·ZSM-5 catalyst,respectively.The conversion and selectivity of 650-1 catalyst decrease by8.4%and 0.47%at 240?reaction temperature,compared with 550-1nNiMoO_x·ZSM-5 catalyst,respectively.