Catalytic Performance Of Transition Metal Doped Ag/MCM-41 For Formaldehyde Reaction

Formaldehyde(HCHO),as indoor gaseous pollutants directly affects human health,its removal has become the focus of modern research.In this paper,thermal catalytic oxidation technology is used to purify formaldehyde,among which the choice of catalyst is more important.The precious metal silver(Ag)is relatively cheap and has a good prospect in HCHO catalytic oxidation reaction.However,the low temperature activity of Ag is poor.Therefore,in this paper,a variety of transition metal-doped Ag/MCM-41 catalysts were prepared by one-pot method.Through the regulation of different transition metal doping and support morphology,the influence of Ag active site on the catalyst and support morphology on the catalytic oxidation activity of formaldehyde at low temperature was studied.The main conclusions are as follows:(1)The effect of Ce on the catalytic oxidation performance of Ag/Ce-MCM-41 catalysts with different Si:Ce molar ratios was studied by doping transition metal cerium(Ce).The results showed that the addition of a small amount of Ce was beneficial to the interaction between Ag and the support,and improved the dispersion of Ag particles on the surface of the catalyst.The particle size of Ag particles decreased from 15 to 5-10 nm.When Si:Ce=1:1,the reductivity of oxygen adsorption on the upper surface of the catalyst is enhanced,and the mobility and activity of oxygen species on the surface are improved.More oxygen vacancies are generated on the catalyst,and the highly reactive oxygen O2-adsorbed on the surface can promote the activation of oxygen molecules,and finally enhance the catalytic oxidation performance of HCHO.(2)By adjusting the morphology and doping different transition metals(Fe,Ce and Mn),the performance of the catalysts doped with different transition metals on the spherical morphology was studied.The results showed that the formaldehyde catalytic activity on the surface of the spherical MCM-41 catalysts supported by several transition metals was higher than that of amorphous MCM-41 catalysts.Different kinds of transition metal doping can have different effects on the Ag state and oxygen species on the catalyst Ag/Fe-MCM-41(sphere)catalyst can support a high content of Ag particles,the average size of 6.42nm,which is conducive to the generation of more contact between Ag and Fe,promote the generation of more reactive oxygen species(Oads),and ultimately improve the catalytic oxidation performance of HCHO.(3)The characterization results of Ag/Al-MCM-41(sphere),amorphous Ag/Al-MCM-41 and Ag/MCM-41 show that a large number of surface adsorbed oxygen(oads)species can be produced on Ag/Al-MCM-41(sphere)and amorphous Ag/Al-MCM-41 materials compared with undopedal.Compared with amorphous Ag/Al-MCM-41 catalyst,Ag/Al-MCM-41(sphere)material can form more acidic sites,which can enhance the interaction between metal and support,and ultimately facilitate the low-temperature catalytic oxidation of HCHO.