Study On The Catalytic Oxidation Of Hcho On Ag-based Supported Catalysts

As an easily available metal,Ag has been widely applied in removing HCHO and shown excellent abatement efficiency.In this paper,a series of Ag/OMS-2 catalysts are prepared by a redox precipitation method.And then the effects of Ag loading as well as the preparation method on catalytic oxidation of HCHO are investigated.During the catalyst preparation process,the surface of OMS-2 is reduced and corroded by H2O2(Mn4+→Mn2+),at the same time Ag+is reduced to Ag0 and precipitates on the surface defects of OMS-2,obtaining highly dispersed Ag0 nanoparticles.Among x%Ag/OMS-2 catalysts with x%Ag loading,the 12%Ag/OMS-2 catalyst exhibits the highest activity for HCHO 100%conversion at 60 ℃,when the conditions is GHSV=60000 ml/(g·h),400 ppm HCHO,about 50℃ lower than the complete oxidation temperature of OMS-2.The characterization results reveal that Ag nanoparticles are uniformly dispersed on the surface of the OMS-2 rod with a size of d=2.4 nm and exposed Ag(111)crystal faces in 12%Ag/OMS-2 catalyst;And there are abundant low-valence manganese ions(Mn3+ and Mn2+),lattice oxygen(Olat)and Ago on the surface of the catalyst surface,indicating that the addition of Ag increases the content of Mn vacancies,oxygen vacancies and Ago active sites on it,thus promoting the oxidation performance of HCHO.In-situ DRIFTS analysis was used to further study the reaction mechanism of formaldehyde on this series of catalysts.The oxidation activity of 12%Ag/OMS-2 catalysts preparaed by different method follow the order of 12%Ag/OMS-2-RP(redox precipitation method)>12%Ag/OMS-2-PVA(NaBH4 reduction method under PVA protection)>12%Ag/OMS-2-IM(impregnation method)>OMS-2,related to low-valence manganese ions,lattice oxygen and Ag0 content.The in-situ DRIFTS analysis confirms that the catalysts containing Ag can shorten the HCHO oxidation process,namely the intermediate DOM adsorbed on Mn is transferred to Ag,which accelerates the conversion of DOM to formate and refigure to CO2 and H2O;But the reaction path of HCHO at 12%Ag/OMS-2-RP catalyst is changed:after DOM is converted into formate,it is further oxidized to unstable bicarbonate,which is more easily to decompose into the final product at low temperature,so it has the best catalytic activity.