Study Of NiO-MO₃/γ-Al₂O₃（M=W,MO） Catalysts And Their Catalytic Behaviors For The Isobutane Selective Oxidation Reaction

NiO-WO3/γ-Al2O3and NiO-MoO3/γ-Al2O3catalysts were prepared bystepwise impregnation method. The catalysts were characterized by X-raydiffraction, FT-Raman spectroscopy, temperature programmed reduction,NH3-temperature programmed desorption, UV-diffuse reflectance spectrum. Theeffects of M/(Ni+M)[M=W,Mo] ratio on surface structure，distribution of activespecies and catalytic performance for selective oxidation of isobutane wereinvestigated. Furthermore, the effects of calcination temperatures, preparationmethod and different supports on the performance of the oxidation dehydrogenationof isobutane were systematically studied.The influence of W/Ni ratio on the performance of the oxidationdehydrogenation of isobutane was investigated. It was found that Ni/W ratios have asignificant impact on surface active species of catalysts. WO3crystal and Ni-Al spinelare mainly observed when the W content is high. However, in Ni-rich catalysts, inwhich Polytungstate, NiWO4and Ni-Al spinel species are mainly observed on thesurface of catalysts. Addition of W at a proper amount obviously improves thecatalytic performance of catalyst for selective oxidation of isobutane and the numberof strong acid sites on the catalyst surface. The catalysts have the best performancefor selective oxidation of isobutane when W/(Ni+W) ratio is0.2. At690℃,i-C4H8:O2=16:8and SV1500h-1, the isobutene selectivity was74.7%while theisobutane conversion was41.6%, which is associated with dehydrogenation capabilityof active species, lattice oxygen activity and surface acidity of the catalyst.Ni/Mo ratios also have an influent on the performance of the oxidationdehydrogenation of isobutane. In Mo-rich catalysts, MoO3disperse phases are mainlyobserved while NiMoO4composite oxides are mainly observed in Ni-rich catalysts.Addition of Mo at a proper amount improves the acidity of the catalyst surface.Ni-Mo-0.4have the best performance for selective oxidation of isobutane. At630℃,i-C4H8:O2=16:8and SV1500h-1, the isobutene selectivity was67.22%while theisobutane conversion was25.79%, respectively.The influence of calcination temperatures, preparation method and differentsupports of NiO-WO3/γ-Al2O3and NiO-MoO3/γ-Al2O3catalysts on theperformance of the oxidation dehydrogenation of isobutane was also discussed. Theresults show that the Surface species structure and dispersion were affected by different calcination temperatures. The interaction between active constituent andsupport was intense when the calcination temperatures was high.Different preparationmethod have a significant impact to the composition of Surface species, the dispersioneffect of W(or Mo) was favorable when dip Ni first.