Catalytic Decomposition Of Formaldehyde By Modified Birnessite-Type Manganese Dioxide

With the development of science and society,people pay more attention on the air quality in the indoor environment.As we all know,formaldehyde?HCHO?is one of the major gaseous pollutants in the indoor environment.Researchers have made many efforts to develop high-performance material for HCHO removal.Noble-metal-based catalysts tend to possess high activity,while their application is restricted by their high cost.It's essential to develop cost-effective material for HCHO removal,which is of great demand.This research focuses on the modification of birnessite-type manganese dioxide with different preparation approaches,doping of different kinds of metal ions at different ratio to promote the catalytic activity.In the meanwhile,a series of characterization methods have been used to illustrate the mechanism of reaction.First,a series of birnessite-type MnO₂ were synthesized with different precursors?KMnO₄;KMnO₄-?NH₄?₂C₂O₄;KMnO₄-MnSO₄?,different preparation approaches?calcination method;hydrothermal method;solution method?and at different preparation temperatures?1000°C;200°C;90°C?.After doping of different dopants?cobalt?II?nitrate;cerium?III?nitrate;nickel?II?nitrate;ferric?III?nitrate;potassium nitrate;potassium carbonate?,the HCHO removal activity of as-synthesized catalysts were compared.The results indicated that cerium?III?nitrate modified birnessite exhibit the highest activity.And the appropriate doping molar ratio?Ce/Mn?was considered to be no more than 5:10.Based on the results mentioned above,cerium modified birnessite?Ce-MnO₂?with different doping ratios were synthesized via a redox reaction between KMnO₄ and?NH₄?₂C₂O₄ in the presence of Ce?NO₃?₃.The as-synthesized samples were characterized by XRD,SEM,TEM,EDS,BET,H₂-TPR,XPS,ICP-AES,Raman and in situ DRIFTS to study the reaction mechanism.The results indicated that,upon the existence of doping cerium,the growth of birnessite was inhibited,which led to smaller particle size and higher specific surface area.Grain boundaries were observed on the surface of birnessite at low doping ratio.The increasing oxygen vacancies and surface adsorbed oxygen species greatly promoted the HCHO removal activity at low temperature.The modified material at nominal doping ratio of 1:10 exhibited the best activity,which completely converted HCHO into CO₂ and H₂O at 100°C and showed higher activity than non-modified birnessite at room temperature.Cerium modified birnessite material is a promising catalyst for indoor air purification due to the high activity and popular price,which is also of great practical value.