Synthesis Of TiO₂ Based Monolithic Catalysts And Their Performance For CO Oxidation

TiO2-based nano materials and their monolithic catalysts are widely applied in many fields.As common used catalytic materials,metal substrate monolithic catalyst has advantages of excellent thermal conductivity and high mechanical strength.However,activity decline will occur under long-term work due to the failure of binder or the mismatch of thermal expansivity at interface,which will cause the falling-off of active ingredient film.Therefore,the synthesis strategy of metal substrate monolithic catalyst with strong adhesion strength to solve the problem that the active component film is difficult to fix should be investigated.In order to obtain the TiO2 based monolithic catalyst with both strong adhesion strength and high performance,the PEO technique assisted with hydrothermal process is used to in-situ grow TiO2 nanosheet on flexible Ti mesh,and CO oxidation is used as probe reaction to evaluate the catalytic activity of synthesized catalysts.The performance is optimized by ions doping and surface modification.The excellent medium temperature zone activity can be realized by doping Fe3+ ion and modifying different morphologies Fe2O3 nanostructures on TiO2 support.After that,Co3O4 nanowires or nanosheets with excellent low temperature activity are modified on the surface of TiO2 to improve the catalytic stability of traditional Co3O4 catalysts.And then,to further cut the costs,CuO nanoparticles with lower price are modified on the surface of TiO2 and the influence of particle size and morphology on catalytic performance is also investigated.The whole catalytic reaction process and active sites are investigated.Finally,both Fe2O3 and CuO nanostructures are modified on TiO2 nanosheets,and the catalytic temperature has significant reduction with the function of interaction between them.The preferential oxidation of CO oxidation performance evaluated under ultrahigh space velocity shows good application prospects in more fields.The main research contents and conclusions are as follows:(1)TiO2 support with metallurgical bonding is in-situ grown on flexible Ti mesh through PEO technology combined with hydrothermal process.The Fe3+ ions are doped into TiO2 lattice with the help of the layered titanate structure.Compared with pure TiO2 nanosheets,there are more chemisorbed oxygen and oxygen vacancies on the FeTiO2 surface,which ensure the excellent catalytic activity.In order to obtain more active component,the Fe2O3 nanostructures with different density and morphology(large particle,small particle,nanothorn and nanosheet)are modified on TiO2 nanosheets,and their specific area,surface chemical states etc are also investigated.Among them,Fe2O3 nanosheets catalyst has the best catalytic activity(completely oxidize CO at～250 ℃).In addition,the mass loss calculated after ultrasonic process shows the strong adhesion strength of monolithic catalysts in this work directly.(2)Co3O4 nanostructures are modified on TiO2 nanosheets through homogeneous precipitation method and hydrothermal process respectively.The effects of Co(NO3)3 concentration,urea concentration,water-bath temperature,deposition time etc on morphology and loading amounts of Co3O4/TiO2 catalysts are studied.The surface chemical states and the CO oxidation property are also investigated.The optimized catalyst has excellent low-temperature performance and it can maintain 100%conversion at continuous 40 h test.It is obvious that the good thermal conductivity of Ti substrate and strong adhesion strength contribute a lot to the catalytic stability.(3)The low-priced CuO particles are deposited on TiO2 nanosheets successfully.The research shows that the excessive urea concentration and deposition time will lead to the local accumulation of CuO with large size.By comparing the morphology,surface chemical states and catalytic activity of CuO catalysts grown in acidity,alkaline and reductive deposition solutions,it can be seen that the CuO-U has the smallest particle size,higher specific area,lowest reaction temperature and Ea,confirming that CuO particle size has an important influence on catalytic activity.And then,hydrothermal method is used to grow ultrafine CuO particles to obtain higher lowtemperature performance.The catalytic mechanism is given priority to MvK mechanism at low temperature area,while the L-H mechanism at high temperature.The adsorption site of CO in the whole catalytic process is Cu+,and the intermediates are carbonate and bicarbonate,confirming the important role of stable Cu+ site.(4)The CuO particles with fine particle size and good dispersion are modified on the surface of Fe-TiO2 nanosheets.Compared with CuO/TiO2,there are more chemisorbed oxygen,active oxygen species and Cu+ active sites on the surface of CuO/Fe-TiO2 catalyst.The doping of Fe3+ ions can loosen the lattice oxygen at the interface of CuO and TiO2,showing the excellent catalytic performance.Furthermore,a series of CuO-Fe2O3/TiO2 monolithic catalysts with different Cu/Fe atomic ratios are successfully prepared by stepwise deposition process.It can be seen that 20FeCuO catalyst has more active surface and higher specific area.The complete oxidation of CO can also be achieved below 90℃ with the help of strong interaction between CuO and Fe2O3.The selective CO oxidation performance is also tested at ultra-high space speed(72000 h-1).Compared with the single oxide,the modification of bimetal oxides can achieve obvious higher conversion rate and wider active temperature window.It also provides new ideas for the design of multifunctional monolithic catalysts.