Preparation And Catalytic Performance Of Porous LaFeO₃for The Oxidation Of Carbon Monoxide And Toluene

Carbon monoxide and most of volatile organic compounds （VOCs） emitted fromindustrial and transportation activities pollute the atmosphere and are harmful tohuman health. Therefore, it is highly urgent to strictly control the emissions of COand VOCs. Catalytic oxidation is one of the most effective pathways to eliminate COand VOCs, in which the key issue is the availability of high-performance catalysts.Although supported noble metal catalysts are highly active at low temperatures, thehigh cost limits their wide applications. Perovskite-type oxides exhibit good catalyticactivities at high temperatures. If perovskite-type oxides are prepared into the oneswith porous structures, they would possess higher surface areas and more amounts ofsurface active sites that favor the adsorption and activation of reactant molecules, andhence their catalytic activities would be improved. Therefore, developing thestrategies to prepare porous and high-surface-area perovskite-type oxides with highperformance for the oxidation of CO and VOCs is of academica and practicalsignificance. In this thesis, we adopted ultrasonic-assisted hard-templating method tosuccessfully generate porous orthorhombic LaFeO₃（denoted as LFO） catalysts. Thephysicochemical properties of the catalysts were characterized by means oftechniques, such as X-ray diffraction （XRD）, scanning electron microscopy （SEM）,transmission electron microscopy （TEM）, selected-area electron diffraction （SAED）,nitrogen adsorption-desorption （BET）, X-ray photoelectron spectroscopy （XPS）, andhydrogen temperature-programmed reduction （H₂-TPR）. The catalytic activities ofthese materials were evaluated for the oxidation of CO and toluene. The main resultsobtained in the thesis are as follows:（1） Wormhole-like porous orthorhombic LFO-1and LFO-2as well asparticle-aggregated macroporous LFO-3and LFO-4catalysts were preparedusing the ultrasonic-assisted repeated impregnation method with lanthanum andiron nitrates as metal source, ethanol aqueous solution as solvent, and KIT-6,SiO₂nanospheres, CMK-1, and carbon spheres as hard template.（2） There were discrepancies in surface area, surface adsorbed oxygen speciesconcentration, and low-temperature reducibility of the final LFO catalystsprepared with different hard templates.（3） The LFO-1and LFO-2catalysts obtained with KIT-6and SiO₂nanospheres ashard template exhibited higher surface areas （138and65m²/g, respectively）,whereas the LFO-3and LFO-4catalysts obtained with CMK-1and carbonspheres displayed a lower surface area of1215m²/g.（4） Among all of the as-prepared LFO catalysts, the LFO-1catalyst possessed the largest surface area, the highest oxygen adspecies species concentration, and thebest low-temperature reducibility. The iron in the LFO catalysts was present inthe forms of Fe⁴⁺and Fe³⁺.（5） Under the reaction conditions of CO concentration=1vol%, CO/O₂molar ratio=1/20, and space velocity （SV）=20,000mL/（g h） or toluene concentration=1000ppm, toluene/O₂molar ratio=1/400, and SV=20,000mL/（g h）, theporous LFO catalysts outperformed the bulk counterpart. The LFO-1catalystshowed the highest activity: the T_10%, T_50%, and T_90%（corresponding to thereaction temperatures required for achieving the conversion=10,50, and90%）were125,155, and180oC for CO oxidation, and130,200, and253oC fortoluene oxidation, respectively.（6） Based on the characterization results and catalytic activity data, we believe thatthe larger surface area, higher oxygen adspecies species concentration, and betterlow-temperature reducibility as well as the developed wormhole-likemesoporous structure of LFO-1was responsible for its excellent catalyticperformance for the oxidation of CO and toluene.