Preparation Of Carbon-supported Noble Metal Catalysts And Their Applications For The Removal Of Hcho At Room Temperature

As a common indoor pollutant,formaldehyde originated from a wide range of sources,and prolonged exposure to formaldehyde gas will cause a serious of disease,seriously threatening human health and safety,so it is urgent to eliminate formaldehyde in an efficient and environmental friendly way.Among the several of methods to remove formaldehyde,catalytic oxidation of HCHO is one of the most effective methods,which oxidize formaldehyde to carbon dioxide and water through catalysts.At present,the difficult points of catalytic oxidation of formaldehyde are to design and develop a catalyst which can oxidize high concentration of formaldehyde completely at low temperature.Carbon-based catalysts are a good choice in this field,carbon-based materials possess abundant types,the preparation method is simple and carbon catalysts are easy to be modified.So in this article,we investigated the properties of several carbon-based catalysts for the oxidation of formaldehyde,revealed the structure-activity relationship of catalysts and explored the reaction mechanism of formaldehyde oxidation.Firstly,the catalysts with activated carbon as the support,noble metal,transition metal oxide and noble metal-transition metal oxide composites as the active components were synthesized.We also investigated the efficiency of catalysts for HCHO oxidation under different temperature and reaction conditions.The results showed that 100 ppm HCHO could be completely oxidized to carbon dioxide and water at 30℃ through 1.5%Pt/AC.However,noble metals are scarce and expensive.Therefore,we reduced the content of Pt of catalysts,meanwhile the catalytic efficiency of catalysts were improved by adding promotor and modifying support.It was concluded that doping a small amount of cerium oxide can improve the reactivity of Pt/C catalyst.The characterization of O2-TPD,in-situ DRIFTS etc.indicated that cerium oxide and platinum could form synergistic effect,providing more reactive oxygen species for the catalyst,which is a key factor for HCHO oxidation.The catalyst was doped with nitrogen atoms by ammonia calcining to modify the activated carbon support.Combind the results of previous chapter we prepared 0.7%Pt-0.8%CeO2/NAC.100 ppm of formaldehyde could be fully oxidized through the sample at 25℃.And the long period of experiments showed that 0.7%Pt-0.8%CeO2/NAC possessed superior stability.HRTEM,XPS characterization proved the presence of electronic migration between nitrogen and platinum atoms.The nitrogen-doped carbon sites can be used as anchors to promote the dispersion of platinum,and the highly dispersed metal state of platinum was the most important active center of the catalyst.Finally,the carbon spheres with regular morphology and uniform particle size were synthesized by hydrothermal method using glucose as the carbon precursor,and the transition metal oxide shell was coated on the surface of the spheres.The activity test results showed that the ranking of acticities of catalysts were:Pt/CS@CeO2>Pt/HCS@CeO2>Pt-CeO2/CS>Pt/CS,and the HCHO conversion of 0.7%Pt/CS@CeO2 was 86.33%at 25℃.Cerium oxide was evenly wrapped on the surface of the carbon sphere,which could fully contact with platinum and form the Ce-O-Pt bond.In order to explore the reaction process of formaldehyde over the catalyst,the mechanism of HCHO oxidation reaction was characterized by In-situ DRIFTS.