Highly Effective Supported Catalysts For Low Temperature Elimination Of VOCs

Volatile organic compounds?VOCs?emission are extremely harmful to the atmospheric environment and human health.Catalytic oxidation ranks among the most efficient techniques for VOCs end treatment.This thesis is aim to study the catalysts in VOCs'removal by photocatalytic oxidation and catalytic combustion,mainly the relationships among their preparation,structure,surface chemistry and catalytic performance.Two types of the most universal VOCs,formaldehyde and toluene,are taken as the model VOCs.TiO₂/ACF is applied in photocatalytic removal of formaldehyde.The catalytic performance of supported copper-manganese oxides and platinum catalysts in catalytic combustion of toluene are deeply investigated,through careful control of the preparation conditions.TiO₂/ACF is prepared using strong-acidic TiOSO₄ solution and in-situ urea homogeneous precipitation.By controlling the acid concentration,preparation temperature and time,calcining temperature,the best photocatalyst TiO₂/ACF can be obtained,with anatase titania nanoparticles homogeneously spreading over ACFs.Abundant C-Ti bond and surface hydroxyls are mainly responsible for the high photocatalytic activity of TiO₂/ACF,which overwhelmingly suppress the catalyst prepared by simple impregnation.Citric acid and sodium carbonate are used for precipitation preparation of the supported copper-manganese oxides.The as-prepared CuMn6Ox/MCM-41 consists of MnCO₃ and?-MnO₂ after calcined,and in catalytic combustion of toluene,can obtain 98%conversion at a temperature as low as 220°C,without deactivation after running 120 h,and have as good performance in wet air.The investigation in the relationships among preparation,characterization and catalytic performance demonstrate that MnCO₃ and?-MnO₂ are both active phases,which are stabilized even after high temperature calcination due to the existence of citric acid and copper.Besides,citric acid can inhibit the accumulation of copper to the surface,increase the active surface manganese species,and thus improve the catalyst's activity.The reduction of KMnO₄ by HCl is also adopted for the preparation of the supported copper-manganese oxides,by adding copper salt to it.The obtained CuMn9Ox/MCM-41contains a hierarchical structure including?-MnO₂ nanorod and K₂Mn₄O₉ nanoslice networks,and can almost totally remove toluene at 230°C by catalytic oxidation,without deactivation after running 120 h.Cu²⁺can stabilize the metastable K₂Mn₄O₉,and the derived manganese vacancies account for the high activity.On the other hand,water vapor would decrease the catalytic activity.Alternating HCl by ethylene glycol for KMnO₄reduction can obtain a catalyst with only one phase,K₂Mn₄O₉,and the catalyst shows as excellent catalytic performance in wet air as in dry air.It is concluded that the K₂Mn₄O₉phase with Cu²⁺incorporation can be a highly active phase in catalytic combustion and of outstanding resistance for water vapor.For the noble metal catalyst in toluene catalytic combustion,ethylene glycol reduction is utilized for preparation,and the chemistry and physical structure are found to be essential to the catalyst activity.The small amount of TiO₂ in the inert support MCM-41,can have better interaction with the noble metal,and improve the surface content of Pt,and thus the catalyst's activity.Pt/Ti-MCM-41 can catalyze toluene at160°C with a conversion higher than 98%.Further,mesoporous titania is synthesized and used as the support,and the catalyst Pt/mTiO₂ can catalyze toluene oxidation with higher than 95%conversion at 145°C,which is quite a high level in the literature report.