本文通过改进的水热法制备了孔径较大的有序介孔SBA-15,其孔径(Dp)为10.1 nm,并采用浓盐酸、三甲基氯硅烷(TMCS)和3-氨丙基三乙氧基硅烷(APTES)对SBA-15表面进行了羟基、甲基和氨基改性处理.以嫁接不同表面官能团的SBA-15为模板,合成了一系列菱方晶系钙钛矿型介孔Lao.8Sro.2CoO3氧化物,系统地研究了模板SBA-15的表面性能对Lao.8Sro.2CoO3氧化物结构和性能的影响.X射线衍射(XRD)图谱表明,外表面引入-CH3,内表面羟基化和引入-NH2的模板有利于合成结晶度较高的、物相单一的钙钛矿结构氧化物.小角XRD图谱、高分辨率透射电子显微镜(HRTEM)图像以及N2吸附测试结果表明,所制备的催化剂为介孔结构.CO氧化的催化活性测试表明,采用表面改性的模板合成的Lao.8Sro.2CoO3氧化物表现出较高的催化活性和稳定性,在140℃时可以实现CO的完全转化,连续使用100 h后催化剂的催化活性几乎没有下降.X射线光电子能谱(XPS)、H2程序升温还原(H2-TPR)和O2程序升温脱附(O2-TPD)测试结果表明,催化剂表面丰富的吸附氧物种,高价态的Co离子,钙钛矿结构中Sr在表面富集,及优良的低温氧化还原性是催化活性提高的主要原因.%Mesoporous SBA-15 with mesopore diameter up to 10.1 nm was prepared by a hydrothermal method,and was further functionalized to obtain different surface properties.Thus-prepared SBA-15 was employed as a template to synthesize rhombohedrally crystallized mesoporous La0.8Sro.2CoO3 perovskite via a nanocasting method.The surface properties of the SBA-15 were adjusted by treatment with concentrated hydrochloric acid,trimethylchlorosilane (TMCS),and 3-aminopropyltriethoxysilane (APTES).A series of characterization techniques verified that all the synthesized templates possessed ordered two-dimensional hexagonal mesoporous structure,and the surface was successfully modified with methyl and amino groups.The mesoporous perovskite structure was formed in the samples and the surface properties of SBA-15 significantly influenced the structure and properties of La0.8Sr0.2CoO3 perovskite oxides.Wide-angle X-ray diffraction patterns suggested that the modified silica templates were conducive to the formation of pure perovskite frameworks with good crystallinity.The catalysts also possessed mesoporous structure,as confirmed by small-angle XRD patterns,high-resolution transmission electron microscopy images,and nitrogen adsorption analysis.Moreover,the La0.8Sr0.2CoO3 materials synthesized using surface-functionalized templates exhibited relatively higher catalytic activity and stability in CO oxidation.Complete CO conversion could be achieved at 140 ℃ using the thus-prepared Lao.8Sro.2CoO3 materials,and no significant loss in catalytic activity was observed after 100 h of on-stream reaction experiments.X-ray photoelectron spectroscopy,H2 temperature-programmed reduction,and O2 temperature-programmed desorption experiments revealed that the existence of Co4+,Sr enrichment in the perovskite structure,and high content of adsorbed oxygen species play a critical role in the enhanced catalytic activity of the catalysts.We also proposed the possible reasons for the effect of surface properties of the silica templates on the structure and properties of the La0.8Sro.2CoO3 nanomaterials.
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