Synthesis of La-Co-O Mixed Oxides via Polyethylene Glycol-Assisted Co-Precipitation Method for Total Oxidation of...

La-Co-O mixed oxides (LCO) were prepared by co-precipitation method with the presence of polyethylene 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 oxidation 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. Particularly, 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 La2O3 and Co3O4. The addition of PEG was favorable for the formation of LaCoO3 perovskite. Particularly, the addition of PEG-6000 effectively suppressed the agglomeration of LaCoO3 perovskite, 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.