Study On Assemblyand Ozone Decomposition Property Of Transition Metal Hydrotalcite

Some industrial and office places are prone to concentration of ozone,which exceeds the threshold value in the national Ambient Air Quality Standard,harming human health.Catalytic decomposition has become the most concerned method for ozone removal due to its high efficiency,environmental friendliness and economy.Transition metals play an important role in ozone catalytic decomposition due to their low cost and redox properties.Hydrotalcite has a unique two-dimensional layered structure and tunable layer composition and electronic structure.In this thesis,transition metals such as Co,Fe,Ni were introduced into LDHs layers,and the types,interactions,the effects of metal valence,hydroxyl groups on the surface of hydrotalcite and surface defect on ozone decomposition were investigated,revealing the catalytic mechanism of LDHs catalytic decomposition mechanism.The main research contents of this paper are as follows:1.Using the controllability of the composition of hydrotalcite laminates,a one-step liquid membrane reactor synthesis method was used to prepare LDH catalytic materials with large specific surface area,which could provide more active sites for the ozone decomposition reaction.After evaluating the catalytic performance of ozone decomposition,it is found that the performance of CoFe-LDH exceeds that of other materials and could be maintained at about 100%conversion within 12h.This can not achieved by other LDH materials or hydrotalcite with Co and Fe as catalytic centers alone.2.In view of the excellent performance of CoFe-LDH catalytic material for ozone decomposition,characterization and analysis were carried out by combining experimental and theoretical methods.Through XPS and H₂-TPR,it is found that the main reason for the excellent performance of the material is the interaction between Co and Fe,reducing the valence state of Co and improving the reducibility of the catalyst.Theoretical calculations reveal the mechanism of action of Co and Fe:Co is favorable to*O₃→*O+*O₂,and Fe is favorable to*O+O₃→*O₂+O₂.Especially after ozone is enriched on the surface of CoFe-LDH,every step of the reaction that the catalyst participates in can proceed spontaneously,which may be the reason for the ultra-high catalytic decomposition ability of CoFe-LDH.Combining O₂-TPD with theoretical calculations,Fe element contributes to the desorption of O₂,and CoFe-LDH has the lowest desorption temperature,which promotes the desorption of gas on the surface of the catalysts.3.In order to further understand the relationship between the material structure and catalytic performance of CoFe-LDH,the surface properties of the laminate structure of CoFe-LDH were adjusted to explore the effects of metal valence,hydroxyl and defect on ozone decomposition.By means of step-by-step oxidation,acid etching,and growth temperature control,it is found that Co with low oxidation state is beneficial to the consumption of ozone.OH with a large number of lone pair electrons and a small number of metal defect as adsorption sites can adjust the electron distribution on the surface of the material,which is in favor of the performance improvement of LDH catalytic materials for ozone decomposition.