Study On Catalytic Combustion Performance And Reaction Mechanism Of Ti-based Nanocatalyst Synthesized By Flame Spray Pyrolysis

Catalytic combustion is a very promising technology for the removal of gaseous pollutants at low concentrations.High-performance catalysts are one of the key points to achieve the complete purification of pollutants at lower temperatures.Flame spray pyrolysis is considered to be an advanced method for the synthesis of nanoparticle catalysts.Its excellent properties bring new opportunities for the preparation of supported catalysts and perovskite catalysts.In this paper,many catalysts for the removal of common gas pollutants（methane,carbon monoxide,formaldehyde,toluene）with high efficiency have been developed.Besides,the reaction mechanism and path during the catalytic process have been studied by combining in-situ FTIR and density functional theory.The following works have been carried out:（1）To enhance the thermal stability of catalysts during high temperature,SrTiO₃-based perovskite catalyst loaded with the copper oxides or doped with transition metal at B site have been successfully prepared by flame spray pyrolysis method for high-temperature catalytic combustion of methane.The Cu O-Sr TiO₃ catalyst still exhibits highly dispersed copper species at large Cu O loading,due to the large specific surface area and the formation of 4 nm Cu O quantum dots on Sr TiO₃.In particular,the copper clusters provide the reactive oxygen species sites for the copper-loaded samples,thus reducing the energy of oxygen vacancy formation and improving CH₄ catalytic activity.The B sites partial substitution of Sr TiO₃（B=Co,Fe,Mn,Ni,Cu）with different valent metal cations is conducive to the formation of vacancies and the excellent performance in catalytic combustion.Meanwhile,Sr TiO₃-based perovskite materials synthesized by flame spray pyrolysis have good thermal stability and water resistance.（2）To improve the low-temperature catalytic combustion performance of SrTiO₃-based perovskite catalyst,Sr_1-xNa_xTi_1-yB_yO₃（B=Co,Mn）perovskite catalyst doped with transition metal at A or B site has been successfully prepared by flame spray pyrolysis,for catalytic combustion of CO and HCHO.The perovskite doped at A and B sites has better low-temperature reducibility,larger specific surface area,more surface oxidizing species,thus promoting the HCHO oxidation activity at low temperature.Seven reaction steps of formaldehyde catalytic combustion on Sr TiO₃-based perovskite are identified by in-situ FTIR and DFT methods.The HCO₂ dehydrogenation is a rate-controlled step,and the reaction energy barrier significantly decreases from 221.44 k J/mol to 147.16 k J/mol after Na doping.（3）Photothermocatalytic combustion can significantly improve the low temperature catalytic efficiency of complete removal of CO and HCHO.Highly dispersed hybrid Cu O_xspecies have been successfully formed on TiO₂ by flame spray pyrolysis.The modification of Cu O_x species not only forms highly dispersed nanoclusters,but also increases the vacancy density,reduces the oxygen vacancy formation energy and the band gap,as well as maintains the dynamic balance of Cu⁺and Cu²⁺ions.The excellent water-resistance of the catalysts during Photothermocatalytic oxidation is attributed to the effective removal of water molecules and hydroxyl groups on the surface of the catalysts,while the good low-temperature catalytic performance is due to the higher oxygen species activity under light conditions and the reduction of the production of intermediates such as bicarbonate.（4）The photothermocatalytic synergistic effect has been further utilized to realize the medium-temperature catalytic combustion of toluene.Pt-TiO₂ catalysts with different platinum loads have been prepared by flame spray pyrolysis,where the single-atom Pt has been observed.The single-atom Pt loading can significantly increase the oxygen vacancy density,promote the anatase-rutile phase transition,enhance the separation of electron-hole pair,and improve the activity of surface oxygen adsorption and lattice oxygen under photoexcitation.Therefore,the photothermal catalysis can not only greatly improve the catalytic efficiency of thermal catalytic toluene,but also improve the surface area carbon removal capacity of the photocatalytic catalyst.The photothermocatalytic activity of single-atom Pt-TiO₂ for toluene is significantly higher than that of CuO_x-TiO₂.The catalytic rate-control steps are all the C=C fracture of maleic anhydride to acetic anhydride,but the maximum reaction energy barrier of single-atom Pt-TiO₂ decreased from 188.74 k J/mol to112.03 k J/mol.（5）Finally,the influence of parameters prepared by flame spray pyrolysis on the performance of nanocatalyst has been discussed,and the magnification design of the preparation technology has been carried out to lay a foundation for engineering application.The results show that regulating the preparation parameters of flame spray pyrolysis can obviously affect the catalytic performance.Furthermore,a laboratory scale flame spray pyrolysis burner is numerically simulated by computational fluid dynamics（CFD）method.By studying the flame combustion,flow and residence time at high temperature in the material synthesis process,a design scheme of continuous large-scale preparation of titanium dioxide nanoparticles by flame spray pyrolysis is proposed.Finally,compared with impregnation method and sol-gel method,flame spray pyrolysis method has better economic performance.