Catalytic Performance Of Vanadium And Iron Modified Phosphotungstate For Selective Oxidation Of Methanol

In this paper,vanadium and iron modified phosphotungstate(Fe VPW)was prepared by simple mixing-precipitation method with iron nitrate,ammonium metavanadate and H₃PW₁₂O₄₀ as raw materials.The morphology,composition and structure were characterized by X-ray powder diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS).The results show that the prepared material is composed of Fe PW(iron phosphotungstate),V₂O₅and Fe VO₄ crystalline phases.The catalytic performance of vanadium and iron modified phosphotungstate materials for the selective oxidation of methanol to methylal under the action of molecular oxygen was evaluated by using a fixed bed high-pressure micro reactor,which showed excellent catalytic activity.The effects of key reaction parameters such as burning temperature,reaction time,temperature and pressure,flow rate of O₂,methanol and N₂ on reaction activity and selectivity were optimized.The optimum burning temperature and reaction conditions were determined as follows:reaction temperature 200 ^oC,reaction pressure 0.75 MPa,methanol flow rate 0.247mmol/min,nitrogen flow rate 0.614 mmol/min oxygen flow 0.205 mmol/min.Under these optimized conditions,the conversion of methanol was 70%and the selectivity of DMM was 96.7%.At the same time,various components V₂O₅,Fe V,Fe PW,VPW and PW(obtained by burning NH₄VO₃,NH₄VO₃+Fe(NO₃)₃,NH₄VO₃+PW and PW at 300 ^oC respectively)and the effects of surface acidity on the catalytic performance were prepared,and the active components on the surface of the catalyst were determined.The adsorption behavior of methanol on the surface of Fe VPW material and its components was studied by in-situ infrared technology.It was confirmed that the active centers of Fe VPW material for methanol oxidation were VO_x and Fe PW crystal phases.In addition,the service life and stability of the catalyst were also discussed.The results showed that the conversion of methanol remained between 65%-70%and the selectivity of Dimethoxymethane was more than 96%in the 9-17h of the reaction.It shows that Fe VPW catalyst has excellent service life and operational stability.