Catalytic Behaviors For Isobutene Selective Oxidation Of MoVBi-AlPO₄ Catalysts

Selective oxidation of isobutene to methacrolein(MAL) is a key step for methylmethacrylate product using isobutene as raw materials. In this paper, the MoV-AlPO₄and MoVBi-AlPO₄ catalysts were prepared by the Sol-Gel method. The surfacecomposition and structure, physical and chemical properties, lattice oxygen activityand selective oxidation of isobutene of the catalysts were systemically studied byusing the techniques of XRD, BET, Raman, TPR, IR, UV-Vis DRS and micro-reactor.MoV-AlPO₄ is mainly composed of MoO3, V2O5 and AlPO₄. The loading amountof molybdenum, vanadium and calcination temperature has a great effect on thedispersion and coordination of molybdenum and vanadium oxides, activity of latticeoxygen species. With the increase of the loading amount of molybdenum, vanadiumand calcination temperature, the molybdenum oxide and vanadium oxide intetrahedral coordination which is highly dispersed on the surface of bulk phase AlPO₄was gradully transformed into octahedral coordination, crystal MoO3 and V2O5, andthe reduction temperature of lattice oxygen decreases firstly and then increases.Theaddition of Bi to the MoV-AlPO₄ had great influence on the structure of catalysts. Theaddition of Bi oxide obviously improved the dispersion of molybdenum oxide on thesurface through the strong chemical interaction between the molybdenum oxide andBi oxide, and a new phase Bi2Mo3O12 was formed. Furthermore, Bi significantlyenhanced lattice oxygen activity of the MoV-AlPO₄ catalyst.The mainly products of selective oxidation of isobutene over MoV-AlPO₄ catalystswere MAL, acetone, acetic acid and COx. The active component loading amount andcalcining temperature of catalysts has a major impact on isobutene conversion andselectivity of MAL. The catalyst pore structure, dispersion of Molybdenum speciesand the redox properties were responsible for the catalytic properties, which were alsorelated to the coordination of Mo active species. For MoV-AlPO₄ catalysts, under theoptimum reaction conditions (360℃, i-C4H8:O2=1:2), the isobutene conversion33.88% and MAL selectivity 49.06% can be obtained. Own to better dispersion ofmolybdenum oxide and the formation of a new crystalline phase Bi2Mo3O12 whichaccelerated the transfer rate of gas active oxygen and lattice oxygen, the addition ofBi significantly improved MAL selectivity of the MoV-AlPO₄ catalyst. For MoV0.3Bi0.3-AlPO₄ catalysts, under the optimum reaction conditions (360℃,i-C4H8:O2=1:2), the results of isobutene conversion 45.65% and MAL selectivity75.82% can be obtained.