Flame Synthesis Of Ceria-based Catalysts And Their CO Oxidation Performance

CO poses a serious hazard to the atmospheric environment and human health.In recent years,with the continuous improvement of people's living standards,residents'requirements for indoor air quality are getting higher and higher,and CO pollution in indoor and closed/semi-enclosed spaces has attracted extensive attention.CO-contaminated places including in indoor and closed/semi-enclosed spaces exhibit the characteristics of high humidity,complex pollutants and sudden pollution.The synergistic interaction between the active species and the CeO2 support affects the structure and dispersion state of the active species,as well as the redox performance of the support,which is a key factor determining the CO catalytic activity and water resistance during catalytic oxidation.However,the synergistic interaction mechanism is not in-depth understood currently,and less attention were paid on its influences on the intermediates of the CO catalytic oxidation process.The oxygen defect concentration and the interaction between the active species and the CeO2-based support were regulated by flame spray pyrolysis(FSP)method with doping a second active component.In this research,a series of CeO2-based catalysts with of high-efficiency CO catalytic activities and water resistance,as well as a catalytic module for rapid removal of CO were prepared by FSP method.Furthermore,in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTs)was used to capture the surface information of the catalysts during CO oxidation.The synergistic interaction mechanism between the active species and the Ce02 support as well as its influences on the reaction intermediates were investigated.Therefore,the relationships among the physicochemical properties,the reaction intermediates and the catalytic activity were deeply understood.The main contents and results are as follows:(1)For indoor and closed/semi-enclosed spaces with high humidity,the CuO-CeO2 catalyst with efficient CO oxidation activity and water resistance was prepared.CuO-CeO2 catalysts with different CuO contents were prepared by one-step FSP,and using cupric acetate anhydrous and cerium acetate as precursors,as well as propionic acid as solvent.The effects of CuO composition on the physicochemical,surface structure and chemical properties of the catalysts were investigated.The synergistic interaction mechanism between CuO and CeO2 and its effect on CO catalytic oxidation with or without water vapor were studied respectively.The results showed that the 14 wt.%CuO-CeO2 catalyst exhibited the superior CO oxidation activity,with the temperature required to achieve a CO conversion of 90%at 98 ? at a high space velocity(SV=60000 mL g-1 h-1),which was attributed to abundant surface defects(lattice distortion,Ce3+,and oxygen vacancies)and high reducibility supported by strong synergistic interaction.In addition,the sample also displayed excellent stability and resistance to water vapor.Significantly,in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTs)showed that the strong synergistic interaction led readily to dehydroxylation and CO adsorption on Cu+at low temperature in the CO catalytic oxidation process.Furthermore,with the presence of water vapor,there was also a positive effect on the formation of fewer carbon intermediates even with the adverse effect on the access of CO adsorption,and consequently,the catalyst exhibited good water resistance.(2)Doping Mn into the CuO-CeO2 catalyst to further increase CO catalytic oxidation activity.MnOx-CuO-CeO2 catalysts with different amounts of Mn dopping were prepared by FSP,and which using manganese acetate,cupric acetate anhydrous and cerium acetate as precursors,and propionic acid used as solvent.The influences of the synergistic interaction among the oxides after Mn doping on the surface structure,chemical properties and electronic properties of the catalysts were investigated.In particular,the mechanism of the synergistic interaction,and its influences on the intermediates of the CO catalytic oxidation were studied.The results showed that the 1Mn-Cu-Ce sample(Mn/Cu molar ratio of 1:5)exhibited superior catalytic activity for CO oxidation.In situ DRIFTs analysis revealed that the enhanced activity was correlated with fine textual properties,abundant chemically adsorbed oxygen and high lattice oxygen mobility supported by strong synergetic interaction,which further induced more Cu+species and formation of fewer carbon intermediates during CO oxidation process.In addition,the 1Mn-Cu-Ce sample displayed the excellent stability with prolonged time on CO stream and the highly resistance to water vapor as the strong interaction among the oxides.(3)Targeting CO mixed gas(CO-based,mixed with small amounts of NOx and hydrocarbons)emitted from high-temperature burners in indoor and closed/semi-enclosed spaces,Zr-doped Pd/CeO2 catalysts with high activity and high temperature resistance were prepared.The influences of the Zr-doped Pd/CeO2 catalysts before and after high temperature aging treatment(heat treatment at 1000 ?for 5 hours)on the surface structure,chemical and electronic properties,as well as the catalytic activity were investigated systemically.The results showed that the PdCe0.50Zr0.50 sample exhibited no phase separation and obvious grain growth before and after aging treatment,and the electron transfer from Pd to the support enhanced the synergistic interaction and promoted the formation of oxygen vacancies on the surface of the support,as well as excited a large amount of surface active oxygen.Therefore,the PdCe0.50Zr0.50 sample showed the best catalytic activity,and could remove CO and NO from the mixture effectively.(4)In the face of sudden CO pollution in indoor and closed/semi-enclosed spaces,a catalytic module for rapid removal of CO was prepared.The catalyst coating layer was deposited on the FeCrAl heating wire by FSP,and the coating exhibited good mechanical bonding force because of the A1 element in the metal substrate diffused outward in the high temperature oxygen-rich environment of flame combustion,and formed the reactive intermediate bonding layer.Therefore,the metal monolith catalyst could maintain stable high activity after 3500 cycles of power-on and off at 320 ?.Furthermore,the coupling of the electric heating could achieve a rapid temperature rise for the metal monolith catalyst.It took only 8 seconds to raise the temperature from room temperature to 320 ?,and it took only 15 seconds to heat up to 680 ?.In addition,the CuO-CeO2 metal monolith catalyst displayed a higher CO reaction rate than its particulate catalyst,and displayed enhanced stability at 320 ?.