Study Of Manganese-Base Catalysts For Catalytic Wet Air Oxidation Of Phenol

Phenol is one of the common water contaminants,decomposed it into harmfulness CO2 or at least less harmful compounds has profound significance.At present,catalytic wet air oxidation(CWAO)is an effective method to degrade phenol in water.Many previous studies have shown that MnCeOx catalysts demonstrating remarkable activity for the degradation of phenol.However,the stability of MnCeOx catalyst has not been studied intensively.Herein,we have developed and prepared a novel MnCeOx catalyst that has high activity as well as stability by modifying preparation methods and optimizing the Mn-Ce composite.Furthermore,the mechanism of high efficiency and stability for the as-prepared catalysts were also studied.In order to reduce the cost of the catalyst thus towards commercialization,we have also developed a new approach to synthesize MnOx,which demonstrate a higher activity and stability than the MnCeOx to degrade phenol at very mild conditions.In this thesis,the activity and stability of the catalysts were determined by TOC,HPLC and AAS.Different techniques including XRD,BET,H2-TPR,O2-TPD,XPS,TEM and elemental analysis were used to characterize the chemical and structural distinctions between different catalysts.The main finds of this thesis are as follows:The novel MnCeOx catalyst with Mn/Ce ratio of 9/1 was prepared by a two-step redox/hydrothermal process that shows high activity and stability to degrade phenol.It can completely convert phenol and remove more than 90%of TOC at very mild condition(70 ?).More importantly,the novel catalyst can be used three cycles without losing its catalytic activity and Mn leaching is almost negligible.It have been found that the high activity and stability of the catalyst are mainly due to the high concentration of reactive Mn4+ and surface active oxygen species.The high-valent Mn species can be reduced easily and give higher oxidation potential toward the oxidation of adsorbed phenol.On the other hand,the high mobility of surface active oxygen species can further help to improve the oxidation performance of the catalyst.In addition,the high concentration of Mn4+ might also contribute for the anti-leaching of Mn species.In order to reduce the cost of catalyst,MnOx mono-metal oxide,which also shows high activity and stability at 70 ? was prepared for phenol oxidation..It has been proved that the high stability of this catalyst is mainly because of the self-recovery of the redox ability of the catalyst at reaction conditions.During the reaction,the surface valence state of the catalyst is a dynamic process.When phenol was oxidized,the Mn species of the catalyst was reduced at the same time,and follow by re-oxidation to high valence states.However,the accumulation of carbon(coke)deposits on catalysts surface still remain,which might cause the coverage of the catalyst active sites.Furthermore,it was also discovered that carbonaceous deposits would block the catalyst pore structures,resulting in the decrease of the catalytic activity of catalysts.This issue is subject to further studied.Finally,the catalyst developed in this thesis also has good potential to the real industrial wastewater treatment.Except for phenol removal,the synthesized novel MnOx catalyst can remove more than 30%of TOC when used for actual wastewater at ambient temperature and pressure.More importantly,the catalytic activity showed only a slight decrease after used for 3 cycles.