Nano Oxides Supported Metal Catalysts For CO Oxidation Reaction

The low-temperature CO oxidation catalysts have long been used in three-way catalytic converters.However,to date,it is still challenging to achieve high performing low cost alternative catalysts.Herein,ceria and manganese IV oxide which are versatile materials in numerous applications were used as catalysts or catalyst supports.In this dissertation,there will be included three main categories.At first,the crystal plane effect of ceria was studied by depositing 1 wt%of copper.Secondly,the effect of catalyst preparation on optimizing the performing of copper-manganese catalysts was explored using deposition precipitation and incipient wetness impregnation methods.And thirdly,the impact of the synthesis of manganese? oxide was examined by reflux and hydrothermal syntheses.The structure-activity relationships of as-prepared catalysts were investigated via X-ray diffraction(XRD),N2 adsorption-desorption,transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),temperature-programmed reduction and temperature-programmed desorption(TPR/TPD),and in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS).1.During the last decades,copper-ceria catalysts have been known as very effective catalyst for CO oxidation,of which the chemical behavior has also been considerably studied.Nevertheless,the impact of the different crystal surfaces of CeO2 on the CO oxidation activity of copper-ceria catalysts is still ambiguous and requires deeper insights.Herein,we deposited 1 wt%of copper on CeO2 nanocubes mainly exposing {100} planes(1CuCe NC)and nanorods(1CuCe NR)exposing high contents of {110} facets,respectively.These two samples were used as catalysts for CO oxidation.1CuCe NC achieves full conversion of CO at 130?,whereas 1CuCe NR displays only 50%of CO conversion at the same temperature.The difference in catalytic activities was reflected by temperature-programmed reduction by hydrogen(H2-TPR)and temperature-programmed desorption of carbon monoxide(CO-TPD)analyses,conforming the excellent reducibility of the 1CuCe NC catalyst which comes from the weak interaction between the Cu and CeO2 support.Moreover,in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS)studies indicate that {100} planes of ICuCe NC facilitate the generation of active Cu(I)sites,resulting in more reactive Cu(I)-CO species during the CO oxidation process.Thus,both the superior redox properties and proper CO adsorption on the active species induce the greatly enhanced catalytic reactivity for the 1 CuCe NC catalyst.2.Recently,the copper-manganese composite(hopcalite)catalyst has been extensively studied for low-temperature CO oxidation reaction.However,based on the several reports on hopcalite catalysts,it still remains as a big challenge due to the severe deactivation under moist condition.In this report,we have developed tremendous performance of CO oxidation catalysts,CuO/?-MnO2 nano-rod materials by synthesizing with deposition precipitation(DP)method.Among various copper loadings,5CuO/?-MnO2 DP sample performed superior activity with the reaction rate of 9.472 ?mol-1·gcat-1·s-1 even at ambient temperature,which was two times higher than that of reported copper-based catalyst.Moreover,the as-synthesized CuO/MnO2 DP catalyst showed remarkable stability in comparison with copper manganese composite catalysts reported in the literature under both conditions of 3%water vapor and without moisture.A correlation between the catalytic CO oxidation activity and textural characteristics was derived via multi-technique analyses.The characterization results showed that the abundant surface oxygen species and proper adsorption of CO on partially reduced copper oxide as Cu(I)-CO are dominant for the enhancement of catalytic performance.3.Over the years,noble metal-based catalysts have been extensively studied for ultra-low temperature CO oxidation reaction.However,due to their high cost and limited availability,seeking a cost-effective alternative has become a great demand.In this work,the dopant free ?-MnO2 catalyst which exhibited highly efficient catalytic property was synthesized by the nitrate-reflux method.The catalyst was extremely active not only for normal gas composition with 3-10 ppm of moisture but also for the dry feed gas with<1 ppm of moisture.Superior to the catalysts developed in previous studies,the ?-MnO2 catalyst achieved tremendous CO oxidation activity showing the nearly full conversion of CO at ultra-low temperature,-70?.With the aid of various analyses,we can deduce that the existence of remarkable redox property and abundant lattice oxygen facilitated the catalytic CO oxidation performance of the synthesized catalyst.