Study On Catalytic Oxidation Of Formaldehyde Over Silver-Based Catalysts

Formaldehyde is a kind of serious indoor air pollutant,the catalytic oxidation which can degrade formaldehyde to CO₂ and H₂O is effective eliminate formaldehyde.Supported noble metal catalysts possess excellent catalytic activities of formaldehyde at room temperature.However,the high cost and limited supply of noble metals have been hampering widespread application.Among them,silver displays more suitable for the catalytic oxidation of formaldehyde due to its relatively low-cost and excellent catalytic performance in comparison with platinum.the preparation method and pretreatment conditions of silver-based catalysts have influence on their surface active sites,specific surface area and morphology,thus affect catalytic performance.In this paper,MnO₂ with specific morphology and Co₃O₄-CeO₂ composite support were synthesized by hydrothermal method,Ag and K ions were separately loaded by impregnation method.The effects of the morphology of support and the atom ratio of potassium to silver on the catalytic activity of Ag-K/MnO₂ were investigated,and the effects of in-situ oxidation reduction etc on the catalytic activity of Ag/Co₃O₄-CeO₂ were investigated.Catalysts were characterized by XRD,SEM,H₂-TPR,O₂-TPD,BET and XPS.The catalytic activities of different catalysts are follows:?1?The a-MnO₂ and b-MnO₂ were synthesized by hydrothermal method.The specific surface area of b-MnO₂(102.08 m²·g^-1)are lower than a-MnO₂(119.69 m²·g^-1),and the surface oxygen activity of b-MnO₂ is lower than a-MnO₂,so catalytic activity of b-MnO₂ is lower.?2?The Ag load led to decrease in both surface area,while both surface oxygen activity were significantly increased,so catalytic activity were increased.The specific surface area,surface oxygen activity and catalytic activity of Ag/b-MnO₂ are higher than Ag/a-MnO₂.?3?The effects of various pretreatment methods including in-situ oxidation reduction,NaBH₄ reduction and calcination on the catalytic activity of Ag/Co₃O₄-CeO₂ were investigated,It was found that the catalyst produced by in-situ oxidation reduction has more abundant surface active oxygen and oxygen vacancy,which can provide sufficient space and transfer channel for reactive oxygen species,and all these are helpful to increase the activity of the catalyst.The results indicated that 250 ppm formaldehyde could be completely oxidized to CO₂ and H₂O,at 60?,a space velocity of 36,000 ml·g^-1_cat·h^-1.?4?The electron cloud structure of Ag can more easily activated adsorbed oxygen of catalyst surface,the addition of K can produce OH^-with lone pair electrons in the catalyst surface,and the interaction of Ag and K enables the lone pair electrons to move at the active site,which are helpful to increase the activity of the catalyst.The study showed that atom ratio of potassium to silver is 0.9,at 60?,a space velocity of 36,000 ml·g^-1_cat·h^-1,300 ppm formaldehyde could be completely oxidized to CO₂ and H₂O.The interaction of noble metal and accessory is studied to reduce the amount of the noble metal in catalyst and improve the catalyst activity,which is the main research direction of the noble metal catalysts of formaldehyde catalytic oxidation.