Study On N-butane Catalytic Cracking Of NMoO_x·HZSM-5 For Increasing Propylene

In the paper,a series of nMoO_x·HZSM-5 single-phase complex were prepared by an improved amorphous citric precursor(IACP)method,and characterized by XRD,BET,NH3-TPD and SEM techniques.The catalytic cracking performance of catalysts was evaluated by using the n-butane as model reactant in the continuous fixed-bed microreactor.The XRD patterns indicate that the diffraction peak of HZSM-5 is well preserved and not found the diffraction peaks of Mo Ox in the nMoO_x·HZSM-5 single-phase complex,which demonstrates that the active component is highly dispersed in the nMoO_x·HZSM-5single-phase complex.The active component Mo is located in the cross of Z form channel and straight channel of HZSM-5 in the form of Mo Ox clusters to generate nMoO_x·HZSM-5 single-phase complex,which causes the shrinkage of HZSM-5 lattice cell and reduces the lattice parameters and cell volume,lessens the specific surface area of catalyst.With the increasing of active component Mo,the acidity of nMoO_x·HZSM-5single-phase complex is increased firstly and then decreased.That's because the Mo Ox clusters have stronger adsorption and polarization of H2 O.However,excessive Mo loading covers some of the acidic sites of HZSM-5,causes the acidic center of the nMoO_x·HZSM-5 single-phase complex decrease.The SEM images indicate that the crystalline grain of nMoO_x·HZSM-5 single-phase complex is uniform.Under the reaction temperature 625 ? and gas hourly space velocity 5600 h-1,the nMoO_x·HZSM-5 single-phase complex with Mo content less than 1.00 m% achieved a slightly lower n-butane conversion than that over HZSM-5.However the propylene yield and liquid product yield have a significant addition.When the loading of Mo is more than2.00m%,the n-butane conversion,the propylene yield and the liquid product yield over nMoO_x·HZSM-5 single-phase complex have asignificant reduction.The n-butane conversion over 260-600-0.75m%catalyst reaches 78.88%.The propylene yield is up to 13.19% and liquid product yield reaches 8.55%,which are 2.25 percent and 3.32 percent higher than those of HZSM-5.It exhibited better performance in increasing propylene production.