Interfacial Synthesis Of Manganese Oxides And Their Application In Catalytic Oxidation Of O-xylene

Benzene hydrocarbons such as benzene, toluene and xylene cause serious harm to human health and environment. Therefore, the removment of these pollutants has been one of the important research topics in environmental treatment. Deep catalytic oxidation is one of the most effective methods to remove these benzene hydrocarbons. Owing to the stability of benzene ring, activiating is very difficult. The selection of catalysts is very important on the deep catalytic oxidation of these benzene hydrocarbons. The effective and low-priced manganese oxides are regarded as one of important catalysts. So searching for suitable methods to prepare effective manganese oxides is a very significant subject of this research.In this paper, a series of manganese oxides such as MnO₂ and Mn₃O₄ were prepared by interfacial synthesis method using KMnO₄ and divalent manganese salts as precursors. The influences of various prepared conditions on the structure features and catalytic behavior of MnO₂ and Mn₃O₄ were examined. The methods such as XRD (X-ray diffraction), BET (Brunauer-Emmett-Teller), FESEM(Field emission scanning electron microscope), FTIR(Fourier transformation infrared spectroscopy), LRS (Laser raman scattering spectroscopy) and TG/DTA (Thermogravimetric and differential thermal analyses) were applied to research the microstructure of the catalysts. The main reslts are as follows:1,A series of manganese oxides catalysts were prepared by CCl₄/H₂O interfacial synthesis method using KMnO₄ and Mn(NO₃)₂ solution as precursors, KOH as pH adjusting regent. The as-prepared manganese oxides were used for complete catalytic oxidation of o-xylene. The influence of prepared method, manganese salt, alkali solution, aged time and calcination temperature on the catalyst structure features and the catalytic behavior were primarily examined. Catalytic activities of the catalysts were evaluated in terms of both o-xylene conversion and carbon dioxide yeild. The results showed that the catalytic activity of MnO_x[N-K-48-400] which was prepared by CCl₄/H₂O interfacial synthesis method using KMnO₄ and Mn(NO₃)₂ solution as precursors, pH≈8, aged time 24 h and calcination temperature 400 oC was excellent, which could converse 0.06 vol% o-xylene into carbon dioxide and water at 190 oC. XRD,BET and SEM characterization results showed MnO_x[N-K-48-400] was microcrystalα-MnO₂ nanoparticle. Its specific surface area was 28.962 m²Â·g^-1.2,A series of manganese oxides were prepared using CCl₄/H₂O, petroleum ether/ H₂O, H₂O and isopropyl alcohol/ H₂O as solvents and KMnO4 and MnCl₂ solution as precursors. The influence of organic solvent dosage(such as CCl₄, petroleum ether, isopropyl alcohol), concentrations and moral ratio of reactants on the compose and catalyst structure features were examined. XRD,BET and SEM characterization results showed Mn₃O₄ of tennis spheres and solid spheres were obtained by CCl₄/H₂O, petroleum ether/H₂O interfacial synthesis method andα-MnO₂ of tennis ball andγ-MnO₂ of urchin were prepared on H₂O and isopropyl alcohol/ H₂O solvent with organic solvent dosage 160 mL , concentrations of reactants C(C denoted 0.25 mol/L KMnO4 and 0.5 mol/L MnCl₂ solution), KMnO4 / MnCl₂ 1:1.5. Their specific surface area were 90.018 m²Â·g^-1 , 61.489 m²Â·g^-1 , 157.315 m²Â·g^-1 and 276.827 m²Â·g^-1 respectively.The large specific surface area of Mn₃O₄ with organic solvent dosage 160 mL , concentrations of reactants C, molar ration of reactants 1:1.5, by CCl₄/H₂O and petroleum ether/ H₂O interfacial synthesis method were used for complete catalytic oxidation of o-xylene and compared with that of Mn₃O₄ which was prepared in H₂O. The results showed that the catalyst Mn₃O₄ which was prepared by CCl₄/H₂O interfacial synthesis method exhibited excellent catalytic performance, which could converse 0.06 vol% o-xylene into carbon dioxide and water at 240 oC.3,A series of manganese oxides were prepared via CCl₄-petroleum ether /H₂O interfacial synthesis method by changing concentrations of reactants, reaction tempreture and moral ratio of reactants. XRD,BET and SEM characterization results showed microcrystal MnO₂ and Mn₃O₄ of mesoporous spheres with concentrations of reactants C, reaction tempreture 25 oC , moral ratio of reactants 1:1.5 were obtained. Its specific surface area was 313.782 m²Â·g^-1. The influence of pH, concentrations of reactants and calcination temperature on the catalyst structure features and the catalytic behavior with concentrations of reactants C, reaction tempreture 25 oC , moral ratio of reactants 1:1.5 were primarily examined. The results showed that the catalystsα-MnO₂ with pH=8, concentrations of reactants 0.5 mol/L KMnO4,8 mol/L KOH and 1 mol/L MnCl₂, calcination temperature 400 oC, could converse 0.06 vol% o-xylene into carbon dioxide and water at 210 oC.