Reductive Preparation Of Manganese Oxides And Their Catalytic Oxidating Formaldehyde At Room Temperature

In recent years,the in door environment quality draws more and more attentions of the people.HCHO pollutant has characteristics of long incubation period,lots of release source and long release time.Therefore,improving indoor air quality is closely related to people’s healty,and removing indoor HCHO pollutant attracts people’s great attention.The removal methods of HCHO are varied,such as ventilation,bilolgical purification,adsorption,ozone oxidation,photocatalysis,low temperature plasma technology and catalytic oxidation and so on.Among them,the catalytic oxidation method transition metal oxides has become the focus in the removal of HCHO because of its chatacteristics of high efficiency,no pollution and low price.In this paper,a series of manganese oxides were synthesized thought a simple redox reaction using potassium permanganate as oxidant and methanol and manganese sulfate as reductant.Certain amounts of acid or alkali were added into the reaction system to comtrol the physicochemical property of manganese oxides,which can influent the catalutin oxidation performance of MnOx.And the physical and chemical properities of the synthesized MnOx were studied and characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),Raman spectroscopy(Raman),nitrogen adsorption,X-ray photoelectron spectroscopy(XPS),hydrogen temperature programmed reduction(H2-TPR),inductively coupled plasma atomic emission spectroscopy(ICP-AES)and in situ infared spectroscopy(in situ FTIR).The catalytic oxidation activity of MnOx for HCHO degradation at room temperature was evaluate on the self-built dynamic and static testing system.The mechanism of HCHO degradation catalyzed by manganese oxides at room temperature was explored through the analysis of the intermediate and final products in the process of the formaldehyde degradation.The results show that manganese oxides prepared though the reduction of potassium permanganate by methanol belong to birnessite.Adding acid into the reaction system could increase the specific surface area,reduce the ratio of surface adsorption oxygen and lattice oxygen and lower the reduction temperature of surface adsorption oxygen and the original reduction temperature of lattice oxygen.The manganese oxide prepared under the reaction conditions of 2.7 mL of methanol,9 g potassium permanganate and 1 mL sulfuric acid has the highest reactivity for HCHO degradation at room temperature.The formaldehyde degradation rate reached 91% while the carbon dioxide yield is 89%.The manganese oxide prepared though the reduction of potassium permanganate by manganese sulfate was belong to cryptomelane with 2 × 2 tunnel structure.And after adding alkali into the reaction system,the manganese oxides change into layered birnessite.Adding alkali into the reaction system could increase the specific surface area,improve the ratio of surface adsorption oxygen and lattice oxygen and lower the reduction temperature of surface adsorption oxygen and the original reduction temperature of lattice oxygen.The manganese oxides prepared in the the 2:3:2 molar ratio of n potassium permanganate,manganese sulfate and sodium hydroxide exhits the highest reactivity for the HCHO degradation at room temperature.The HCHO degradation rate arrives 95%,and the carbon yield is 57%.