Ionothermal Synthesis Of Vanadium Phosphate Catalysts For Catalytic Reactions

Vanadium phosphate?VPO?own to its complex structural characteristics which as a composite oxide catalyst,has been widely used in the selective oxidation of alkanes,especially the selective oxidation of C2-C4 alkanes,dehydration reactions.The preparation methods of the VPO catalyst mainly include hydrothermal method and alcohol solvothermal method.The VPO catalyst prepared by the conventional hydrothermal method and the alcohol solvothermal method has a low specific surface area and a low catalytic activity in the selective oxidation reaction of an alkane.Ionic liquids have low vapor pressure,good thermal stability,and good solubility,it have a great advantages as a reaction solvent in the preparation of porous materials an d special morphology materials.In this paper,a mixed solution of different proportions of ionic liquid and water as a reaction solvent to synthesize a different proportion of VPO catalyst.It was used in the selective oxidation of cyclohexanol to synthesize cyclohexanone and cyclohexanol to synthesize cyclohexene to investigate its catalytic performance.The specific research contents are as follows:?1?Using mixed solution of different proportion of ionic liquid and water as reaction solvent,H₃PO₃ as reducing agent and part phosphorus source,V₂O₅ as vanadium source,synthesis of a series of VPO catalysts in different proportions.The effects of different ratios of mixed solutions of ionic liquid and water as reaction solvents on the morphology of the VPO catalyst precursor and the final VPO catalyst were investigated in detail.SEM showed that the VPO catalyst prepared using pure water as the reaction solvent by hydrothermal method which is a large piece of flaky compound.As the proportion of ionic liquid increases,the size o f the large piece is gradually reduced,and the morphology is transform spherical Particle,when the proportion of ionic liquid is 80%and completely ionic liquid as the reaction solvent,the VPO catalysts exhibits a complete spherical particle morphology,and the specific surface area is the highest at this time.Characterized by XRD,as the proportion of ionic liquids increases,the VPO catalyst changed from the VOHPO₄·?H₂O crystal phase to the amorphous state.The synthesized VPO catalysts precursor was calcined at a high temperature in an air mixture containing 1.5%n-butane,and all were converted into a vanadyl pyrophosphate phase and a small amount of amorphous vanadium phosphate phase.The above results show that ionic liquids have extremely important effects in the synthesis of VPO catalysts.VPO-80 catalyst synthesized by ion thermal method and VPO-W catalyst synthesized by hydrothermal method for the selective oxidation of cyclohexanol to cyclohexanone at low temperature?70^oC?The yield of cyclohexanone on VPO-80 catalyst was 57.98%,while The yield of cyclohexanone on the VPO-W catalyst was only 21.41%;The reaction for dehydration of cyclohexanol to cyclohexene at high temperature?270^oC?,The yield of cyclohexene on the VPO-80 catalyst synthesized by ion thermal method was 65.11%,while the yield of cyclohexene on the VPO-W catalyst was 52.08%.?2?In the preparation process of VPO catalyst precursor,the morphology of the catalyst was controlled by adding polyethylene glycol during the preparation of the VPO catalyst precursor.The effect of the addition of polyethylene glycol on the morphology and specific surface area of the VPO catalyst precursor and the final VP O catalyst was investigated.The XRD characterization indicated that the VPO-per-G catalyst precursor prepared by this method was in an amorphous state.SEM showed that the morphology of the VPO-G catalyst obtained after calcination was agglomerated together,and the distribution was relatively uniform.By N₂adsorption-desorption and specific surface area measurement,compared to the VPO-80 catalyst prepared without polyethylene glycol the specific surface area of the VPO-G catalyst prepared by adding polyethylene glycol was significantly increased.VPO-G catalyst synthesized by this method and VPO-80 catalyst synthesized by ion thermal method without polyethylene glycol ion is used for the selective oxidation of cyclohexanol to cyclohexanone at a low temperature?70^oC?,the yield of cyclohexanone on the VPO-G catalyst was 67.69%,and the yield of cyclohexanone of the VPO-80 catalyst was 57.98%.The reaction for dehydration of cyclohexanol to cyclohexene at high temperature?270^oC?,the yield of cyclohexene on the VPO-G catalyst was 77.08%,and the yield of cyclohexene on the VPO-80 catalyst was65.11%.?3?The catalytic performance of cyclohexanol catalyzed reaction on VPO catalysts synthesized by the above three different methods was systematically investigated.At low temperature?70^oC?,VPO catalyst as an oxidation catalyst will selectively oxidize cyclohexanol to obtain cyclohexanone;at high temperature?270^oC?,the VPO catalyst as an acid catalyst dehydrates cyclohexanol to obtain cyclohexene.In this paper,a series of factors affecting the conversion rate of the reaction raw materials and the selectivity of the target product were investigated in detail,such as reaction time,reaction temperature,raw material ratio and reaction space velocity,a certain regular result was obtained.