Controlled Preparation And Catalytic Performance Of Co₃O₄/3DOM La_0.6Sr_0.4CoO₃and Au/3DOM LaCoO₃for The Oxidation Of Carbon Monoxide And Toluene

Volatile organic compounds （VOCs） emitted from industrial and transportationactivities are harmful to the atmosphere and human health. Therefore, it is highlyurgent to strictly control the emission of VOCs. Catalytic oxidation is one of the mosteffective pathways to eliminate VOCs, in which the key issue is the availability ofeffective catalysts. Perovskite-type oxides exhibit higher catalytic activities andstability, and can be used to catalyze the oxidative removal of VOCs.Three-dimensionally ordered macroporous （3DOM） perovskite-type oxides possesshigher surface areas that are expected to show good catalytic performance in theoxidation of VOCs. With3DOM materials as support, one can prepare their supportedtransition-metal oxide and gold catalysts. With the aid of the strong interactionbetween the metal and support, the catalytic activity and stability can be improved.Therefore, preparing3DOM-structured perovskite-type oxide-supported transition-metal oxide and nanosized gold catalysts and elucidating the relationship between thephysicochemical properties and catalytic performance of the materials are ofacademic and practical significance. In this thesis, we adopted the in situ poly（methylmethacrylate）（PMMA） microsphere-templating and gas bubble-assisted polyvinylalcohol-protected reduction methods to prepare x wt%Co₃O₄/3DOM La_0.6Sr_0.4CoO₃（x=010） and xAu/LaCoO₃（x=1.547.63wt%） catalysts, respectively. Thephysicochemical properties of the materials were characterized by means of thetechniques, such as X-ray diffraction （XRD）, scanning electron microscopy （SEM）,transmission electron microscopy （TEM）, selected-area electron diffraction （SAED）,nitrogen adsorption-desorption （BET）, inductively coupled plasma atomic emissionspectroscopy （ICP-AES）, X-ray photoelectron spectroscopy （XPS）, and hydrogentemperature-programmed reduction （H2-TPR）. The catalytic activities of the sampleswere evaluated for the oxidation of toluene, and their kinetic parameters werecalculated. The main results obtained in the thesis are as follows:1. x wt%Co₃O₄/3DOM La_0.6Sr_0.4CoO₃（LSCO; x=0,2,5,8, and10） were fabricatedby adopting the in situ PMMA-templating strategy with the metal nitrates as metalsource, L-lysine as surfactant, ethylene glycol and methanol aqueous solution assolvent, in which the3DOM LSCO and Co₃O₄possessed the rhombohedralperovskite and cubic structures, respectively; the as-prepared x wt%Co₃O₄/3DOMLSCO samples displayed a macropore size of120140nm, a macropore thicknessof1325nm, and a surface area of3032m2/g. The8wt%Co₃O₄/3DOM LSCOcatalyst showed the higher oxygen adspecies concentration and betterlow-temperature reducibility. Under the conditions of toluene concentration=1000ppm, toluene/O₂molar ratio=1/400, and space velocity （SV）=20,000mL/（g h）, x wt%Co₃O₄/3DOM LSCO catalysts performed well in the oxidation of toluene,with the8wt%Co₃O₄/3DOM LSCO catalyst exhibiting the best performance: at aSV of20,000mL/（g h）, the T10%, T50%, and T90%（corresponding to the reactiontemperatures at toluene conversion=10,50%, and90%） were158,210, and227oC, respectively. The apparent activation energies （4358kJ/mol） of the x wt%Co₃O₄/3DOM LSCOcatalysts were lower than those （5967kJ/mol） of the8wt%Co₃O₄/bulk LSCO and bulk LSCOcatalysts. Therefore, it is concluded that theexcellent catalytic performance of8wt%Co₃O₄/3DOM LSCO was associated withits higher oxygen adspecies concentration and better low-temperature reducibility.2.3DOM LaCoO₃was prepared using the PMMA-templating method with the metalnitrates as metal source, L-lysine as surfactant, and ethylene and methanol aqueoussolution as solvent. xAu/3DOM LaCoO₃（x=1.547.63wt%） were generated viathe gas bubble-assisted PVA-protected reduction route with HAuCl4as Au sourceand NaBH4as reducing agent. The as-prepared LaCoO₃and gold showed therhombohedral perovskite and cubic structures, respectively. The xAu/3DOMLaCoO₃samples displayed a macropore size of118135nm, a macropore wallthickness of1124nm, an Au particle size of410nm, and a surface area of2429m2/g. The7.63Co₃O₄/3DOM LaCoO₃catalyst showed the higher oxygen adspeciesconcentration, better low-temperature reducibility, stronger interaction between theAu nanoparticles and3DOM LaCoO₃. Under the conditions of tolueneconcentration=1000ppm, toluene/O₂molar ratio=1/400, and SV=20,000mL/（gh） or CO concentration=1vol%, CO/O₂molar ratio=1/20, and SV=10,000ml/（g h）, the xAu/3DOM LaCoO₃catalysts performed excellently in the oxidation oftoluene and CO. The7.63Co₃O₄/3DOM LaCoO₃catalyst exhibited the highestactivity: the T10%, T50%, and T90%were136,188, and202oC for toluene oxidation,and61,6, and42oC for CO oxidation, respectively. The apparent activationenergies （31.438.6kJ/mol） of the3DOM LaCoO₃and xAu/3DOM LaCoO₃catalysts were lower than those （49.761.5kJ/mol） of the bulk LaCoO₃and7.56Au/bulk LaCoO₃catalysts for toluene oxidation, and the apparent activationenergies （16.619.4kJ/mol） of the xAu/3DOM LaCoO₃catalystswere also lowerthan those （22.829.3kJ/mol） of the bulk LaCoO₃å'Œ7.56Au/bulk LaCoO₃catalysts.Therefore, we believe that the higher oxygen adspecies concentration, betterlow-temperature reducibility, and strong Au3DOM LaCoO₃interaction of7.63Au/3DOM LaCoO₃was responsible for its excellent catalytic performance fortoluene and CO oxidation.