The Research Of Ag/CeO₂-Co₃O₄ Catalysts On Their Catalytic Performance In Low-temperature Catalytic Oxidation Of Formaldehyde

Formaldehyde,as one of the main indoor pollutants,is seriously harmful to human health.The catalytic oxidation of formaldehyde removal is regarded as the most efficient approach.Among that,the noble metal catalysts are supposed to the optimal materials to formaldehyde abatement due to the excellent catalytic performance at low temperature even room temperature.However,the drawbacks of precious metal like scarcity of resources and high cost restrict its widely commercial application.By contrast,silver-based catalysts are recommended for the most competitive candidate in catalytic oxidation of formaldehyde,since it combines the advantages of high activity at low temperature of precious metals and low cost.In the thesis,we prepared the mixed metal oxides CeO₂-Co₃O₄ support by co-precipitation method,changed the Ce/Co molar ratio and the precipitant during the synthesis process,and loaded different Ag contents via impregnation method to prepare a series of Ag/CeO₂-Co₃O₄ catalysts.In addition,the characterizations of N₂adsorption-desorption,XRD,Raman,H₂-TPR and In-situ DRIFTS were conducted to illustrate the correlation of the physicochemical property and catalytic performance.The main results were listed as follow:1.A series of Ag/CeO₂-Co₃O₄ catalysts were prepared with different precipitants when Ce/Co molar ratio remained 1/19.It was found that T₉₀0 of the various catalysts decreased in the order as follow:Ag/CeO₂-Co₃O₄-NH₄>Ag/CeO₂-Co₃O₄-K>Ag/CeO₂-Co₃O₄-NH₃>Ag/CeO₂-Co₃O₄-Na>Ag/CeO₂-Co₃O₄-OA.The synthesis with oxalic acid precipitant were beneficial to the formation of defect,the increment of Co²⁺and oxygen vacancy,which greatly improved the oxygen molecule adsorption and activation,as well as catalytic activity.2.Various Ag/CeO₂-Co₃O₄ catalysts with different Ag contents were prepared by impregnation method.The catalytic performance of the catalyst gradually increased and then maintained with the increment of Ag.When the Ag loading was 1wt.%,the catalyst exhibited the optimal activity with 100%conversion at 80oC.Of which the catalytic activity maintained even though the Ag loading increased to 2wt.%or 4 wt.%.In addition,when the Ag loading was extremely low for only 0.1wt.%,the complete removal of formaldehyde could still be achieved at 100oC,which was better than most of the Ag-based catalysts at present.3.A series of Ag/CeO₂-Co₃O₄ catalysts were prepared with various Ce/Co ratios.The results demonstrated that all the Ag/CeO₂-Co₃O₄ catalysts exhibited an excellent catalytic performance and the Ce/Co ratio showed a significant impact on HCHO oxidation degradation.Among them,when the catalyst with Ce/Co molar ratio reached 1/19 could completely convert formaldehyde at 80oC.It was found that the partial addition of CeO₂ enhanced the redox property and Co²⁺contents of catalyst,which accelerated the formation of oxygen vacancy.Thus,the activation of oxygen species was promoted,which was conducive to the degradation of HCHO.According to the in-situ DRIFTS results,the decomposition of formates dominated the key step for HCHO oxidation process.