Preparation Of Iron-based Catalyst For Low Temperature Catalytic Oxidation Of CO

CO is a kind of colorless and odourless gas.which poses a great threat on human health and environment,and has been one of the pollutents that need to be governed urgently.Catalytic oxidation method is the most direct,efficient way among the different methods of removing CO.Thus,catalytic oxidation method attached much attention by numerous researchers.This paper mainly investigated the application of Ce modified Fe₂O₃ catalysts in CO oxidation.Also,the different preparation conditions,such as different iron precursor,different pH of the solution during the preparation,different precipitation agent,comparison of the different metal doping on Ce modified Fe₂O₃ catalysts and partial reaearch on reaction mechanism are discussed.A series of characterizations were carried out to investigate the physical and chemical properties of the catalysts,such as XRD,BET,XPS,TEM,H2-TPR,CO-TPD.Uv-vis,FT-IR.The main results are listed as follows:1.Ce modified Fe₂O₃ catalysts show superior catalytic activities towards CO oxidation,which was mainly responsible for the formation of iron-cerium solid solution,which improve the redox ability of the catalysts,a better oxygen capacity and mobility.By loading different cerium,we found that 7.5%CeO2/Fe catalyst shows the best catalytic activity,which owns more Fe²⁺/Fe3+ and Ce3+/Ce⁴⁺.And the content of Fe²⁺ and Ce3+ have close interaction to the formation of oxygen vacancies.2.Studying the influence of the different preparation conditions?iron precursor,pH,precipitation agent?on the catalyst performance.CeO2/Fe catalysts that were prepared by different iron precusors have great effect on CO oxidation.Catalyst made by ferric chloride owns the best performance,which was mainly responsible for the largest specific surface area,strong interaction between iron and cerium as well as a better redox ability.Catalyst made by ferric sulfate shows the least ability.On one hand,the existence of sulfuric acid root covered the surface,reduce the interaction between Fe and Ce;on the other hand,the catalyst possesses a small surface area,which is infavourble for the attachment of CO.Moreover,a poorer redox ability was also responsible for the poorer performance.pH=7 shows the best performance.Too high or too low pH affects the nuclear reaction and crystallization of the sample.At the condition of a low pH.satuation of Ce⁴⁺,Fe3+ and Fe²⁺ can not be guaranteed,resulting partial ions absent the precipitation reaction.Additionally,a slower rates of precipitation and crystallization leads the catalyst an irregular pattern.While increasing pH,more OH-will exist in the solution and resulting in reaction equilibrium to the right,accelerating the formation of crystals.However,continue increasing pH,hard agglomerate may emerged in the catalyst preparation.3.Precipitant has a certain influence for catalytic oxidation of CO.With ammonia as precipitant during preparation of catalyst has a better performance.Mainly due to ammonia ions into ammonia volatilization in the process of preparation,resulting catalysts in a good coprecipitation reaction,enhance the activity of the catalyst,together with a larger specific surface area and better redox ability.With sodium carbonate as precipitant in preparing catalyst shows a poorer activity compared with ammonia,may be due to the presence of sodium ions in the catalyst during prepartion,affecting the formation of cerium solid solution,and the specific surface area is low as well as a poor redox ability.Different rare earth metal doped catalysts have different impact on structure and chemical properties,resulting in different catalytic activity.Er and Nd loading on CeO2/Fe catalyst optimized the structure and chemical properties,improving the catalytic activity.4.Reaction mechanism among different catalysts are varied.In Cu-ZSM-5 catalyst.Cu+ plays a main role towards CO oxidation.Cu+ reacts with the oxygen in the reaction gas to generate Cu-O.Through the breaking of Cu-O.O was occupied to CO in forming CO2.Latter,the Cu²⁺ in the breaking Cu-O was reduced to Cu+,again reacts with the gas of O2 to regenerate the Cu-O.The reaction mechanism followed Langmuir-Hinshelwood reaction mechanism.The preparation of loading Ce on Fe catalyst exists a separation phase and thus there may be two different reaction path.On the one hand,the reaction follows the redox mechanism.Part of the CO in reaction gas react with the surface lattice oxygen on catalyst to generate CO2.In this reaction,surface oxygen vacancies playes an important role.On the other hand,a large amount of CO in the reaction gas reactes with O which was activated by the synergetic effect between Fe and Ce.