Preparation And Toluene Catalytic Oxidation Of Nanocrystal-like Mn-Co Oxides

With the increasing volatile organic compounds emission and its terrible effects on human beings, the removal of VOCs has become a severe issue. As an economical and enviromental control technology, catalytic oxidation has attracted more attention. The important aspect of effective catalytic combustion technology is the development of high-performance catalysts. This work constructed Mn-Co catalysts by various methods and performed activity tests and finally chose an ideal preparation method; through investigating the composition, morphology and activity of Mn-Co catalysts, we developed a Mn-Co catalyst with high activity and stablity.Mn-Co oxides catalysts were prepared by four different synthetic methods (one-step hydrothemal method, two-step hydrothermal method, hydrothermal combined with impregnation and copricipitation) and the catalytic activity for toluene oxidation were measured. The nanocrystal-like Mn-Co sample prepared by two-step hydrothermal process showed excellent activity. Therefore, the two-step hydrothermal method was adopted as the preparation method for Mn-Co oxides. The precursor calcination temperature for Mn-Co sample was350℃.The structure and composition of catalysts were investigated by XRD, XPS and SEM technologies. Through two-step hydrothermal process, a series of nanocrystal-like Mn-Co samples with high puff and porosity were successfully prepared. The Mn-Co catalysts consist of Mn3O4and CO3O4with strong interaction as well as Mn-Co solid solution.By studying the surface structure, physico-chemical property and toluene catalytic activity of the catalysts, we have confirmed an ideal Mn/Co molar ratio. When the Mn/Co molar ratio is1:2, the nanocystal-like Mn-Co sample showed an excellent catalytic activity for toluene oxidation with the complete conversion temperature of250℃and the large reaction rate (18.6×10-4mol/(g-s),4.3×10-4mol/(m2·s)).The formtion process of oxygen vacancy and the influencing factors of toluene catalytic activity were also discussed. Co addition promotes the strong interaction between Mn3O4and Co3O4for Mn-Co oxides. The interaction between Mn3O4and Co3O4contributes to the formation of mutual-doped Mn-Co oxides (Mn-Co solid solution). In this process, the oxygen vacancies are generated along with the electron transfer from Mn3O4to Co3O4, which promote the high reducible oxygen species concentration. The unique structure with large porosity, surface area and the high concentration of reducible oxygen species are mainly responsible for the significant enhancement of catalytic activity for toluene oxidation over Mn-Co oxide samples.The Mn-Co oxides catalysts prepared by two-step hydrothermal process show good stability during the toluene oxidation. The activity is higher than the Mn-Co catalysts reported by other researchers.