Preparation And Catalytic Performance Of La_1-xSr_xMO_3±δ (M=Co, Mn) Nanoparticles For Ethylacetate And Toluene Oxidation

Volatile organic compounds (VOCs) are a kind of main pollutants to the atmosphere and threaten human being's health seriously. Catalytic oxidation has been thought to be one of the most efficient pathways for the removal of VOCs, in which the key issue is the development of highly active catalysts. Perovskite-type oxides La1?xSrxMO3±δ(M = Co, Mn; x = 0, 0.4) have increasingly been received much attention due to their low cost and good catalytic performance in VOCs removal. In this thesis, we (i) prepared La1?xSrxMO3±δ(M = Co, Mn; x=0, 0.4) nanoparticles by using citric acid-complexing method and its combination with a hydrothermal process, (ii) characterized the physicochemical properties of these materials by means of X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopic (XPS), oxygen temperature- programmed desorption (O2-TPD), hydrogen temperature- programmed reduction (H2-TPR) as well as surface area measurements and chemical analysis of transition metal ion oxidation states, and (iii) examined their catalytic activities in the total oxidation of VOCs (ethylacetate and toluene). It has been shown that the prepared La1?xSrxMO3±δ(M = Co, Mn; x = 0, 0.4) catalysts were single phase and of rhombohedral perovskite-type structure with the surface areas ranged from 16 to 32 m2/g, in which the Sr-doped lanthanum cobaltate catalyst derived from the citric acid complexing-hydrothermal synthesis coupled strategy was uniformly distributed nanoparticles with a short rod-shaped morphology, whose particle diameters and lengths were 20~30 and 60~80 nm, respectively. The Mn in La1?xSrxMnO3+δ(x = 0, 0.4) existed in the form of Mn4+ and Mn3+; with the rise in substituted Sr2+ amount, the content of Mn4+ increased whereas the amount of nonstoichiometric oxygen (i.e. excessive oxygen) decreased, but the reduction-oxidation (redox) ability of the catalysts strengthened. The Co in La1?xSrxCoO3?δ(x = 0, 0.4) were present in tri- and di-valency; the Co3+ content, nonstoichiometric oxygen amount (i.e. oxygen vacancy density), and redox ability of the catalysts increased with increasing the amount of Sr2+ substituted. The La1?xSrxMO3±δnanoparticles showed excellent catalytic activities for the oxidation of VOCs (i.e. ethylacetate and toluene), in which the Co-based catalysts outperformed the Mn-based ones. Among the catalysts investigated in the present thesis, the La0.6Sr0.4CoO2.78 catalyst obtained with the exhibited the best catalytic performance in the addressed reactions: under the conditions of VOC (ethylacetate or toluene) concentration = 1000 ppm, VOC/O2 molar ratio = 1/400, and space velocity = 20000 h?1,the temperature required for total oxidation of ethylacetate and toluene was 175 and 225oC, respectively; furthermore, CO2 and H2O were the only products without formation of any other partially oxidized products. Taking into consideration of the physicochemical properties and catalytic activities of La1?xSrxMO3±δ(M = Co, Mn; x = 0, 0.4), it is concluded that in addition to the surface area, the catalytic performance was associated with the structural defect (nonstoichiometric oxygen) concentration and redox ability of these perovskite-type oxide nanomaterials.