| In recent years,Mo-V based complex oxides catalyst has a good application prospect in selective oxidation of light alkane and ammonia oxidation,which has attracted scholar’s attention.Benzaldehyde is an important organic chemical intermediate and has a wide demand in medicine,pesticide,dye,perfume.To date,the oxidative dehydrogenation of benzyl alcohol to benzaldehyde is one of the simplest,efficient and environmental-friendly methods.In this paper,the MoVOx complex oxides were prepared by subcritical water,in the process of preparing the catalyst,change Mo/V molar ratio and subcritical water temperature and post-treatment of MoVOx.The effects of different preparation conditions on the crystal phase,structure and morphology of MoVOx was investigated by XRD,SEM,H2-TPR and BET techniques.Hydrothermal method is the most commonly used method to syntheize of Mo-V-O complex oxides,but this method usually requires a long reaction time,generally 5-48 h.Furthermore,in order to improve the crystallinity and stability of products,a necessary post-heat treatment at550–600℃under a given atmosphere,lasting for several hours,In addition to hydrothermal synthesis method,sol-gel method,coprecipitation method and solvothermal method can also be used to prepare Mo-V-O complex oxides,but their applications are limited by some restrictive factors,such as complex operation,long reaction time,difficult in obtaining precursors and high cost,which is different from the traditional preparation method.Subcritical and supercritical fluids are regarded as being controllable and fast solvent methods in the field of metallic material preparation,due to the adjustable physicochemical properties,simple reaction system,fast reaction rate,and wide applicability of raw materials.More importantly,under sub-and supercritical systems,the crystallization of metalbased products can be achieved in a very short time.This makes the follow-up heat treatment of product no longer necessary,simplifying the preparation process greatly.In the experiment,deionized water was used as the solvent to prepare MoVOxcomposite metal oxide,which was used to provide pressure for the sealed reaction system at a certain temperature.O2 was the oxidizer,Gas phase catalytic oxidation of benzyl alcohol.The experimental results show that the main crystalline phase of MoVox is V0.95Mo0.97O5,The crystal phase and crystal content of MoVox composite metal oxides prepared by different subcritical water system temperatures and Mo/V molar ratios are different,The lower subcritical water system temperature is not conducive to the full reaction of Mo and V elements to form complex oxides.TPR results show that increasing the Mo/V molar ratio can improve the reducibility of MoVox,and then have a favorable effect on the conversion rate.And then have a advantageous effect on the conversion rate,The results of catalytic oxidation of benzyl alcohol showed that the conversion of benzyl alcohol could be improved by increasing the subcritical water system temperature.The selectivity of benzaldehyde reached 98%when the reaction temperature was 250℃,the Mo/V was 1:0.4 and the subcritical water system temperature was 400℃. |
