Study On Catalytic Performance Of NWO_x·HZSM-5 In N-hexane Isomerization

nWO_x·HZSM-5 and nNiWO_x·HZSM-5 catalysts were prepared by complexation of citric acid precursor and incipient wetness impregnation methods,and characterized by XRD,NH₃-TPD,BET and SEM.Catalytic performance of isomerization of n-hexane was evaluated in a self-assembled high pressure micro-reactor.The XRD patterns of nWO_x·HZSM-5 indicated the diffraction peaks of HZSM-5 were preserved well.The diffraction peaks of WO_x were not found,which illustrated that WO_x was highly dispersed in the molecular sieve.W components located in the cross of the Z-shaped and straight channels of HZSM-5 by the solid-state reaction in forms of WO_x clusters,WO_x coordinated with the skeleton oxygen of HZSM-5 to generate nWO_x·HZSM-5 single-phase complexes,which made the crystal cell of HZSM-5 shrink and cell volume abate.The specific surface area and pore volume of nWO_x·HZSM-5 catalysts decreased with the increasing of activation temperature.At the same activation temperature,the specific surface area and pore volume of nWO_x·HZSM-5 catalysts increased at first and then decreased with the augment of W dosage.Acid sites of nWO_x·HZSM-5 decreased with the raising of W dosage and activation temperature,while acid sites of nNiWO_x·HZSM-5 catalysts increased with the enhancing of Ni/W mole ratio.The performance of catalysts were evaluated under pressure of2.0MPa,LHSV 1.0h^-1,hydrogen hydrocarbon ratio of 7:1,reaction temperature 240℃and 260℃.Results showed that the n-hexane conversion and isomerization selectivity of nWO_x·HZSM-5 catalysts decreased with the augment of W dosage.At 240℃,the isomerization selectivity of nWO_x·HZSM-5-600-0.5 reached 25.8%,which was 1.3 per cent higher than that of HZSM-5.Rising of activation temperature,the conversion of n-hexane catalyzed by nNiWO_x·HZSM-5 decreased,while the isomerization selectivity increased firstly and then decreased.Ni/W mole ratio rising from 0.3 to 2.0,nNiWO_x·HZSM-5 catalysts prepared at550℃,600℃and 650℃,conversion and isomerization selectivity increased at first and then decreased.Reaction temperature of 240℃,the isomerization selectivity of nNiWO_x·HZSM-5-600-1.0 reached 28.4%,which was 2.6 per cent higher than that of nNiWO_x·HZSM-5-600-0.0.