Study On Catalytic Wet Oxidation For Harmless-degrading Phenolic Wastewater Over Pt/TiO₂ Catalyst

Phenol is an important chemical raw material and intermediate,widely used in the production processes of pharmaceuticals,textiles,ceramics,etc.However,a large amount of phenol-containing wastewater will be generated during its production and applications.Phenol-containing wastewater seriously damages human life,health and ecological environment,and even makes the natural ecology lose its original balance.Catalytic wet air oxidation(CWAO)is a wastewater treatment technology that can efficiently and harmlessly treat phenol wastewater with great prospects.However,the operation conditions of the existing catalysts are harsh,which result in high requirement and costly for the reactor used.Improving the catalyst’s oxygen activation and delivery capacity is one of the keys to the development of highly efficient catalytic oxidation catalysts.The literature research and the previous research work of the research group have shown that adjusting the electronic interaction between the metal and the support i.e.electronic metal support interaction(EMSI),can change the electronic state and structure of the catalyst,thereby improving the oxygen activation and transfer performance of the catalyst.This thsis takes the classic Pt/TiO2 catalyst as the research object.By using the pre-synthesized Pt nanoparticles,Pt nanoparticles are impregnated and loaded on TiO2(referred to as oil phase method).On the premise of avoiding Pt being wrapped by TiO2,the EMSI between Pt active component and TiO2 support is effectively strengthened,and the electronic structure and state of Pt component and TiO2 support are changed,then a low-temperature and efficient CWAO Pt/TiO2 catalyst for phenol wastewater treatment is developed.The main results are as follows:(1)Compared with the traditional impregnation method,the Pt/TiO2 catalyst prepared by the oil phase method has excellent CWAO catalytic activity for harmless treatment of phenol wastewater.Under the conditions of reaction temperature of 100℃and pressure of 2 MPa,the TOC conversion of 2Pt/TiO2-Oil(oil phase method)catalyst is as high as 88.8%.For Pt/TiO2 catalyst,100℃ is the lowest temperature reported in the literature to achieve a TOC conversion above 85%.However,under the sam reaction conditions,the TOC conversion of 2Pt/TiO2-IM(traditional impregnation method)catalyst is only 39.5%.And the TOF value of 2Pt/TiO2-Oil catalyst is 4 times that of 2Pt/TiO2-IM catalyst.In addition,the Pt/TiO2-Oil as CWAO catalyst can also efficiently convert methanol into harmless CO2 in wastewater.At the temperature of 50℃ and oxygen pressure of 2 MPa,the TOC conversion of 2Pt/TiO2-Oil is as high as 97.8%.However,under the same reaction conditions,the TOC conversion of 2Pt/TiO2IM was only 16.1%,and the TOF value of 2Pt/TiO2-Oil catalyst was 8 times that of 2Pt/TiO2-IM catalyst.(2)The characterization results indicate that the strong EMSI between the Pt active component and the TiO2 support is the main reason for its excellent catalytic performance of 2Pt/TiO2-Oil.The characterization results of XRD and TEM showed that Pt is highly dispersed in 2Pt/TiO2-IM and 2Pt/TiO2-Oil catalysts.CO chemisorption results showed that the Pt active component of 2Pt/TiO2-IM was partially wrapped by TiO2 support,while the Pt of 2Pt/TiO2-Oil catalyst was not,or only a small part was wrapped.The results of Raman characterization confirmed that there is a stronger EMSI between the Pt active component and TiO2 support of 2Pt/TiO2-Oil than that of 2Pt/TiO2-IM.XPS results show that the EMSI of 2Pt/TiO2-Oil is stronger although the TiO2 supports of 2Pt/TiO2-IM and 2Pt/TiO2-Oil both transfer electrons to Pt metal.Therefore,the Pt of 2Pt/TiO2-Oil catalyst has more negative charge and contains higher Ti3+content.The H2-TPR characterization results confirmed that the 2Pt/TiO2-Oil catalyst will have a strong hydrogen spillover phenomenon in the final step of the catalyst preparation(H2 reduction treatment),which will lead to deep reduction of TiO2 support.As a results,the formation of more reductive TiO2 will make electrons more easily transferred to metal Pt,greatly enhancing the metal support electron interaction.Electron-rich Pt and reduced TiO2 promote the activation and transfer of oxygen and accelerate the CWAO reaction of phenol and methanol.Therefore,Pt/TiO2 catalysts with strong EMSI have higher catalytic activity than conventional Pt/TiO2 catalysts.