High Efficient Catalyst For Catalytic Wet Air Oxidation Of Formaldehyde Wastewater

Formaldehyde is widely used in chemical industrial,however,large volumes of wastewater containing formaldehyde are generated in the processes of the production and utilization of formaldehyde.Formaldehyde is seriously harmful to human health thus brings impact to the water environment.Compared with conventional biological treatment,catalytic wet air oxidation(CWAO)is a more efficiently technology to treat formaldehyde wastewater.However,most of the existing catalysts for CWAO of formaldehyde wastewater contains high noble-metal loadings.Moreover,the catalytic performance can not meet the requirement of industrial applications especially having working under higher temperature.This work focused on designing and synthesizing novel catalysts with lower cost,good catalytic activity and stability for CWAO of formaldehyde wastewater under milder conditions.The main results are as follows:1.Among the three studied oxides,TiO2?CeO2 and R-MnO2(Rod-like-MnO2),R-Mn02 is the best support for the Pt-based catalysts.Pt/R-MnO2 exhibited an excellent catalytic performance for CWAO of formaldehyde wastewater.Even at a temperature as low as 50 ?,the Pt/R-MnO2catalsyt,with a loading 0.1 wt%Pt,can remove 82.3%of formaldehyde,while,the conversions of Pt/TiO2 and Pt/CeO2 were only 11.0 and 35.4%under the same conditions.The results of XRD,H2-TPR and XPS indiacted that the good dispersion of Pt metal and the excellet redox property were mainly contributing to the remarkable catalytic performance of Pt/R-MnO2 catalsyt.It was also found that the pH of the solution was lowered during the process of the CWAO,which resulted in the leaching of Pt.2.Based on the Result 1,the effect of MnO2 morphology on the catalytic perforamnce of Pt/MnO2 was futher investigated.Compared with Pt/R-MnO2 and Pt/S-MnO2(Sheet-like-MnO2),Pt/C-MnO2(Cocoon-like MnO2)exhibited higher activity and better stability.The intial conversion of formaldehyde of Pt/C-MnO2 reached a high value of 88.1%.Even after four consecutive reaction,the conversion of formaldehyde was retained as high as 80.8%.However,for Pt/R-MnO2 and Pt/S-MnO2,the formaldehyde conversions were decreased from 82.2 and 82.4%to 16.3 and 35.6%,respectively,after four cycles.The characterization results,including TEM,XPS,H2-TPR and O2-TPD,revealed that the better dipersions of Pt metal,the richer surface oxygen,the easier reduction and the stronger oxidizing ability were related to the excellent catalytic performance of Pt/C-MnO2 catalyst.The ICP analytic results before and after reduction suggested that Pt/C-MnO2 catalyst possessed higher resistance to Pt leaching than Pt/R-MnO2 and Pt/S-MnO2,which attributed to the good stability of Pt/C-MnO2 catalyst.