The Use of Three-Dimensionally Ordered Macroporous (3DOM) LaFeO_3 Perovskites as Oxygen Carriers in Chemical-Looping Reforming of Methane

摘要

Three-dimensionally ordered macroporous (3DOM) LaFeO_3 perovskite-type oxides were synthesized using a polystyrene colloidal crystal templating method. The obtained 3DOM LaFeO_3 was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The effect of the self-assembly methods on the structure of the polystyrene template was also studied. A vertical deposition method obtained a more uniformly ordered polystyrene template than those prepared by centrifugation and evaporation techniques. The solvent and concentration of the precursor solution were the major factors to affect the resulted 3DOM perovskite. SEM analysis showed that samples synthesized with ethanol precursor solvent exhibited a better 3DOM structure than those produced with ethylene glycol, and that 1.0 mol/L may be an optimal precursor solution concentration. XRD and FTIR results suggested that the obtained 3DOM LaFeO_3 was monophasic crystalline perovskite. The reactivity of the perovskite-type oxides was studied using temperature-programmed reduction and multicyclic redox reactions. The methane oxidation performance of the oxides was investigated in a fixed-bed reactor. It was observed that the present 3DOM perovskites have good repeatability, and the available oxygen in the 3DOM LaFeO_3 was higher than that of the same mass of LaFeO_3 nano-particles during the partial oxidation of methane, which was partially oxidized into syngas with a H_2/CO ratio of around 2:1 in a wide time range of the reactions.