Effect Of Ce-Fe Synergism On The Surface Of Fe₂O₃ Fine Particles On Catalytic Performance Of Co Reduction And Denitrification

NOx is one of the important pollutants in the atmosphere.Although NOx in China has been effectively controlled in recent years,it is still difficult to reach the prescribed emission standards.Therefore,how to effectively reduce the emission of NOx is one of the hot issues in current research.CO catalytic reduction of NO is an effective method,and the selective catalytic reduction method?CO-SCR?with CO as reducing agent can remove both CO and NO,which are harmful gases of coal burning.Therefore,it is regarded as a denitrification technology with potential to be widely used.Baiyun obo rare earth tailing is an important secondary resource.At present,it has been proved that it plays a very good effect in CO catalytic reduction of NO in the furnace.Fe and Ce play important roles in the catalytic process.One of the occurrence states of CeCO₃F in rare earth tailings is exhibiting encapsulation-impregnation with Fe₂O₃.Therefore,based on the research of rare earth tailings,this work prepared Ce⁴⁺to Fe₂O₃ complex oxides catalysts and the CO denitrification performance was explored.CeO₂ to Fe₂O₃ catalysts were prepared by three methods:ordinary dipping?OD?,nitric acid dipping?NAD?and nitric acid dipping with hydrothermal treatment?NADH?.The Ce?NO₃?₃ concentration was 0.01,0.05,0.1,0.5 mol/L.The denitrification performance was explored under 700,800 and 900?.Then the synergistic mechanism of Fe-Ce composite oxides was explored by means of H₂-TPR,XRD,SEM,Raman,XPS and TEM.On one hand,the research could make a certain contribution to the exploration of a new type of denitrification catalyst;on the other hand,it is expected to provide a theoretical basis for the study of the catalytic denitrification of rare earth tailings.The main conclusions are as follows:?1?The denitrification performance of catalysts.The results showed that the denitrification activity of the Fe-Ce composite catalyst has a higher denitration efficiency than single iron oxide or cerium oxide at each temperature.The 0.1CeFe catalyst prepared by the NADP method has the highest denitration rate at each temperature;a denitration rate of 99%was reached at 900?.It indicates that there is a synergistic relationship between iron and cerium.Among the three preparation methods,the denitrification performance is ranked as follows:NADH>NAD>OD.?2?Through SEM and XRD results,it was found that the OD samples had the highest dispersion of CeO₂;NAD and NADH samples exhibit shape changes caused by dilute nitric acid solution,which may provide conditions for the formation of embedded solid solution.The XRD results of the reacted samples showed that Fe₃O₄ appeared as an intermediate reaction substance in the samples after the nitric acid impregnation and nitric acid hydrothermal denitration,indicating that CO would reduce Fe³⁺to Fe²⁺in the reaction and then participate in the reaction.H₂-TPR measurements of different preparation methods indicated that the oxidative reducibility of the samples ranked as follows:NADH>NAD>OD.?3?The NADH samples were thoroughly analyzed.XRD results showed that the peak of CeO₂ shifted to a high diffraction angle and the lattice constant became smaller.Raman results showed that the characteristic peak of NADH samples corresponding to CeO₂ showed red shift.Combined with XRD results,it was shown that the hydrothermal nitric acid method could form Fe-Ce solid solution,thus promoting the catalytic reaction.TEM images showed that there were many fine Fe₂O₃ particles formed on the surface of the catalyst due to the thermal decomposition of iron nitrate.H₂-TPR results showed that the three characteristic reduction peaks moved to lower temperature,relative to the single Fe₂O₃;and new peaks related to CeO₂ appeared before300?.This indicates that CeO₂ could improve the surface reducibility of Fe₂O₃.In the three sample groups,the shift amplitude of the characteristic peak,the high temperature reduction window and the characteristic peak intensity of 0.1CeFe behaved better than other samples prepared under different Ce?NO₃?₃ concentrations.The XPS results showed that the presence of cerium oxide could promote the conversion from Fe³⁺to Fe²⁺and the conversion from lattice oxygen to adsorbed oxygen.In turn,the composite oxide could promote the conversion from Ce⁴⁺to Ce³⁺,which is the embodiment of the synergistic effect of Fe-Ce composite oxide.Therefore,composite oxides have higher catalytic activity than single oxide.?4?In general,Fe₂O₃ particles acting as carriers could provide a large amount of lattice oxygen,and the addition of CeO₂ could improve the catalytic activity of Fe₂O₃.NAD and NADH samples could form Fe-Ce solid solution.On the one hand,the release of oxygen from the block to the surface was promoted;on the other hand,fine Fe₂O₃particles can be formed to provide surface oxygen overflow channel,thus promoting the catalytic performance of composite oxides.