聚乙二醇辅助下的La-Co-O 复合氧化物合成及其对苯的完全氧化性能研究

摘要

La-Co-O mixed oxides (LCO)were prepared by co-precipitation method with the presence of poly-ethylene glycol (PEG)as dispersant.The influence of adding different molecular weight of PEG (0,2 000, 6 000,20 000 g·mol-1 )on the physicochemical and catalytic properties of La-Co-O mixed oxides for total ox-idation of benzene was investigated.The samples were characterized by means of N2 physical adsorption,X-ray diffraction (XRD),scanning electron microscopy (SEM),temperature-programmed reduction by H2 (H2-TPR),temperature-programmed desorption of O2 (O2-TPD),and X-ray photoelectron spectroscopy (XPS). The order of catalytic activity was found to be LCO-PEG6000>LCO>LCO-PG20000>LCO-PG2000.Partic-ularly,LCO-PEG6000 exhibited benzene conversion of 99% at temperature as low as 383 ℃,which was 126℃ lower than that of LCO.The characterization result reveals that all samples had a BET surface area of about 9~10 m2 ·g-1 .The XRD result shows that on all samples LaCoO3 perovskite was mainly formed together with a small amount of La2 O3 and Co3 O4 .The addition of PEG was favorable for the formation of LaCoO3 per-ovskite.Particularly,the addition of PEG-6000 effectively suppressed the agglomeration of LaCoO3 perovs-kite,giving rise to small and uniform particles as observed by SEM.Moreover,the results of H2-TPR and O2-TPD indicate that the obtained La-Co-O mixed oxides showed higher reducibility and lattice oxygen mobility, and the Co 2p XPS analysis suggests that more surface Co3+ active species were presented by the addition of PEG-6000.These properties are thought to contribute to the high activity in benzene total oxidation.%以聚乙二醇(PEG)作为分散剂,采用共沉淀法合成 La-Co-O 复合氧化物,考察添加不同分子量的PEG (0,2000,6000,20000 g·mol-1)对复合氧化物的物化性质及苯完全氧化性能的影响。采用N2物理吸附、XRD、SEM、H2-TPR、O2-TPD和 XPS进行催化剂表征。苯完全氧化反应结果显示催化剂活性顺序为LCO-PEG6000>LCO>LCO-PG20000>LCO-PG2000,LCO-PEG6000催化剂在383℃时对苯的转化率达到99%,比LCO低126℃。N2物理吸附实验表明所制备的样品的SBET均为9~10 m2·g-1。XRD分析显示合成的催化剂均为 LaCoO3钙钛矿主相伴生少量 La2 O3和Co3 O4杂相,但添加PEG有利于钙钛矿主相的形成。尤其是添加PEG6000有效地抑制了催化剂颗粒的团聚,合成的样品颗粒均匀且尺寸最小。H2-TPR 和O2-TPD结果表明该催化剂具有更高的还原性能和晶格氧迁移能力,同时 XPS分析显示表面活性 Co3+含量最高,这些性质使其具有最高的催化氧化活性。