Nanosized perovskite-type oxides La 1− xSr xMO 3− δ (M = Co, Mn; x = 0, 0.4) for the catalytic removal of ethylacetate

Abstract

Nanometer perovskite-type oxides La 1− x Sr x MO 3− δ (M = Co, Mn; x = 0, 0.4) have been prepared using the citric acid complexing-hydrothermal-coupled method and characterized by means of techniques, such as X-ray diffraction (XRD), BET, high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and temperature-programmed reduction (TPR). The catalytic performance of these nanoperovskites in the combustion of ethylacetate (EA) has also been evaluated. The XRD results indicate that all the samples possessed single-phase rhombohedral crystal structures. The surface areas of these nanomaterials ranged from 20 to 33 m 2 g −1, the achievement of such high surface areas are due to the uniform morphology with the typical particle size of 40–80 nm (as can be clearly seen in their HRSEM images) that were derived with the citric acid complexing-hydrothermally coupled strategy. The XPS results demonstrate the presence of Mn 4+ and Mn 3+ in La 1− x Sr x MnO 3− δ and Co 3+ and Co 2+ in La 1− x Sr x CoO 3− δ , Sr substitution induced the rises in Mn 4+ and Co 3+ concentrations; adsorbed oxygen species (O −, O 2 −, or O 2 2−) were detected on the catalyst surfaces. The O 2-TPD profiles indicate that Sr doping increased desorption of the adsorbed oxygen and lattice oxygen species at low temperatures. The H 2-TPR results reveal that the nanoperovskite catalysts could be reduced at much lower temperatures (<240 °C) after Sr doping. It is observed that under the conditions of EA concentration = 1000 ppm, EA/oxygen molar ratio = 1/400, and space velocity = 20,000 h −1, the catalytic activity (as reflected by the temperature ( T 100%) for EA complete conversion) increased in the order of LaCoO 2.91 ( T 100% = 230 °C) ≈ LaMnO 3.12 ( T 100% = 235 °C) < La 0.6Sr 0.4MnO 3.02 ( T 100% = 190 °C) < La 0.6Sr 0.4CoO 2.78 ( T 100% = 175 °C); furthermore, there were no formation of partially oxidized by-products over these catalysts. Based on the above results, we conclude that the excellent catalytic performance is associated with the high surface areas, good redox properties (derived from higher Mn 4+/Mn 3+ and Co 3+/Co 2+ ratios), and rich lattice defects of the nanostructured La 1− x Sr x MO 3− δ materials.