Studies On Preparation And Modification Of ?-MnO₂ Based Catalysts And Their Catalytic Oxidation Of Formaldehyde

Due to the widespread use of industrial adhesives,the problem of indoor pollution also ensues,among which formaldehyde gas has the characteristics of high toxicity and long volatility period,which has caused people's attention.Noble metal catalysts have good activity indoors,but their high cost limits their widespread use.Therefore,it is necessary to develop cheap and highly active catalysts in practical applications.In this paper,?-Mn O₂catalyst was prepared by hydrothermal and thermal decomposition methods.The morphology and defect structure of the catalyst were optimized by changing the preparation conditions.At the same time,the formation mechanism and synergistic mechanism of the catalyst were indicated through systematic characterization.A core-shell??-Mn O₂/Ce O₂@Ce O₂?catalyst was developed.First,the ethylene diamine?EDA?+triethylene glycol?TEG?system captures CO₂ to prepare a CO₂ storage material?CO₂SM?,which provides CO₃^2-in the hydrothermal process while reducing the morphology of the precursor.After the reaction of Mn²⁺solution and CO₂SM with different qualities,Mn CO₃ precursors with different morphologies can be prepared.The EDA and TEG remaining in the middle after the reaction can recapture CO₂to prepare Mn CO₃ precursors cyclically.The morphology and structure of the Mn CO₃precursor was adjusted by changing the hydrothermal conditions.Three homogeneous precursors were prepared.The morphological order of the precursors was oblique,the spheres with nano-blocks stacked and the spheres with nano-particles stacked.?-Mn O₂catalysts with different morphologies can be prepared from Mn CO₃ precursors with different morphologies after thermal decomposition.The adjustment of the structure and defects of the?-Mn O₂ catalyst was achieved by this method of hydrothermal decomposition.Among them,the spherical catalyst with nano-particles has the largest ratio and oxygen vacancy defects,and shows good catalytic activity.At 110oC,the?-Mn O₂catalyst can balance 160ppm HCHO,21%O₂,and N₂ gas at 84 L/gcat·h was completely converted at a gas hourly space velocity,and the conversion rate could be maintained above 96%within 72 hours.When hydrothermal reaction of Ce³⁺with Mn²⁺mixed solution and CO₂SM,a competition mechanism appears between the two ions.Mn²⁺generates Mn CO₃ but Ce³⁺forms Ce O₂ in the solution.Finally,a Mn CO₃@Ce O₂precursor is obtained.A catalyst with??-Mn O₂/Ce O₂?@Ce O₂core-shell structure can be obtained by thermal decomposition of the precursor.The two components in the catalyst have a synergistic effect and the catalyst activity is further improved.The synergy mechanism of the two components in the catalyst was systematically characterized.??-Mn O₂/Ce O₂?@Ce O₂catalyst can completely convert the gas?180 ppm HCHO,21%O₂,and N₂ balance?·at 80oC with GHSV=100 L/gcat·h.After that,the conversion remained above 95%in 72 h and above 73.8%in 140 h,suggesting the strong stability of the catalyst at high gas flow rate.