The Study Of Detritiation Catalyst And Its Metal-Support Interaction

Tritium is an important material in fusion reaction.It is essential to protect tritium rigorously,because of its radioactivity.And it is of great difficulty to control tritium because it can permeate through almost all the material,such as stainless steel.Thus,multi-confinement systems as well as tritium cleanup systems are usually applied to prevent tritium leaking to the environment.For gaseous tritium,the method of catalytic oxidation and absorption is the most widely used process so far.Detritiation catalyst is a key point in this method,whose properties impact on the detritiation efficiency.However,few studies focuse on detritiation catalysts especially aims on the particularity of tritium oxidation.Hence,some new detritiation catalysts,including honeycomb catalyst,multifunctional catalysts and thermal stablized catalyst,are studied here.Catalytic activities and performances are comprehensively tested in this study.In addition,Strong Metal-Support Interaction(SMSI)in the catalysts is investigated.The results are summarized as follows:(1)Honeycomb catalysts Pt(Pd)/Al2O3-HC is studied and tested for air detritiation,?-Al2O3 with large specific surface area and thermal stability is prepared as catalyst support.A new method for support coating,sol/slurry mixed solution assisted with ultrasound,is raised for catalyst substrate preparation.The catalyst prepared with honeycomb substrate has less resistance to gas than particle catalyst.As a result,honeycomb catalyst increases the space velocity by 2 orders of magnitude without decreasing the conversion rate of H2.The results validated that honeycomb catalyst is fit for air detritiation with large gas flow and low tritium concentration.(2)Three doping effects are studied for CeO2,and the structrures and properties changes of Zr,Ti,Sn doped CeO2 are analysed.Zr4+ isovalent incorporation brings in structrural effect,greatly enhances the bulk reduction of CeO2.La3+ and Y3+ aliovalent doping is mainly electronic modification,which improves the surface reduction of CeO2.Tix+ and Snx+ volatile valent doping decreases the reduction temperature,and greatly increases the oxigen storage capacity.Zr4+,Ti4+ and Sn4+ doped CeO2 vary in thermal stability,and follow different trend in structure and property change,during aging treatment.For,CeO2-0.2TiO2,unstable Ce2Ti2O7 formed under reducing atmosphere,which has little influence on the redox property of the oxide.However,the seperation of oxide,under oxidizing atmosphere above 800 ?,deteriorated redox property.For CeO2-0.2SnO2,the seperation of oxide happens under both reducing and oxidizing atmosphere.Fortunately,CeO2-0.3ZrO2 is the most stable of the three,which can be used as oxgygen storage support for multifunctional catalyst.(3)The idea of multifunctional catalyst prepared with CeO2-0.3ZrO2 is put forward.The influence of Pt loading on support properties are studied,and Pt/CeO2-0.3ZrO2 exhibits the optimized stability and catalytic performance.The multifunctional catalyst Pt/CeO2-0.3ZrO2-HC,with honeycomb structure,is verified to be suitable for inert atmosphere detritiation,in addition to air detritiation with large gas flow.(4)The Strong Metal-Support Interaction in catalyst Pt/CeO2-0.3ZrO2 is studied,and new insights are reached.The interaction greatly decreases the reduction termperature of support,and promotes the oxidation,dispersing as well as stabilization of Pt.The essence of the interaction is bonding of Pt and O in supports.The bonds of Pt-O and Pt-O-Ce are ascribed respectively to Pt1+ and Pt2+,which are also related to the Pt adsorption sites on CeO2 surface.During support reduction,the bonds bring in O vacancies on CeO2 surface,which activate the lattice O.In addition,the Pt oxide species act as intermediate products during reduction,which decreases the reduction activating energy.For Pt dispersing and stabilization,the interaction plays a key role as follows.First,the interaction inhibits the reduction of Pt oxide species at mild temperature.Second,the interaction prevents the decomposition of Pt oxide species at elevated temperature.Third,the interaction promotes the re-oxidation and re-dispersing of Pt.The last is the most important,which can be employed to prepare catalyst with highly dispersed Pt.(5)A new preparation of single atom catalyst with regular structure is proposed.Single atom catalyst S-Pt/CeO2-0.3ZrO2 is prepared by anti-Ostwald ripenning,according to the different strength of interaction in Pt/Al2O3 and Pt/CeO2-0.3ZrO2.Pt is indeed single atom dispersed on CeO2-0.3ZrO2 suface,with very strong Metal-Support interaction,which greatly enhances the stability of catalyst.Single atom catalyst with regular structure can be prepared,by mixing regular CeO2-0.3ZrO2 substrates with Pt/Al2O3 powder,followed by aging treatment above 600 ?.(6)Ceria-based oxide catalysts and their catalytic mechanisms are studied.Doping effects influence the catalytic performance of oxides.Structural effect enhances the catalytic activity at relatively high temperature(above 150?),while electronic effect avails low temperature(below 150?)activity.Structural and electronic effects coexist in CeO2-0.1La2O3,thus it exhibits best catalytic performance.And the performance is further improved by La3+ and Ptx+co-doping,because both catalytic oxidation mechanisms(Mars-van-Krevelen mechanism and Dissociation-Spillover mechanism)operate in Ce0.78La0.2Pt0.02O2-?.This catalyst is highly active with excellent stability,which avoids the deteriorating of catalyst activity acompanied by ingredient losing.