Synthesis of three-dimensionally ordered macroporous LaFeO3 perovskites and their performance for chemical-looping reforming of methane

Three-dimensionally ordered macroporous (3DOM) LaFeO3 perovskite-type oxides were synthesized using a polystyrene colloidal crystal templating method. The obtained 3DOM LaFeO3 was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The reactivity of the perovskite-type oxides was evaluated using temperature-programmed reduction and multicyclic redox reactions by exposing them to an alternating methane and air atmosphere. The methane oxidation performance of the oxides was investigated in a fixed-bed reactor. The effect of the self-assembly method on the structure of the polystyrene template was also studied. A vertical deposition method yielded a more uniform and orderly polystyrene template than those obtained by centrifugation and evaporation techniques. The solvent and concentration of the precursor solution were the major factors to affect the prepared 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 LaFeO3 was pure crystalline perovskite. Two kinds of oxygen species were found to exist on the 3DOM perovskites: surface adsorbed oxygen and bulk lattice oxygen. The surface oxygen contributed to the complete oxidization of methane to CO2 and H2O because of its higher reactivity, while the bulk lattice oxygen tended towards partial methane oxidation to H2 and CO. The available oxygen in the 3DOM LaFeO3 was higher than that of the same mass of non-3DOM LaFeO3 during the partial oxidation of methane. Methane was partially oxidized into syngas with a H2/CO ratio of around 2:1 in a wide time range of the reactions. The generated H2/CO = 2 syngas was suitable for subsequent gas-to-liquids processes, such as Fischer-Tropsch and/or methanol synthesis.

摘要采用超声波辐射法制备了具有介孔结构的高浓度氮掺杂TiO2纳米晶(N/TiO2). 采用N2物理吸附/X射线粉末衍射/X射线光电子能谱/透射电镜/光致发光谱和紫外-可见漫反射光谱等手段对N/TiO2进行了表征. 以波长为400–660 nm的可见光为光源, 以水体污染物邻苯二甲酸二甲酯为降解对象, 考察了不同制备方法对N/TiO2光催化性能的影响. 结果表明, 超声波辐射使氮掺杂浓度提高了2.2倍, 该法制备的N/TiO2同时具有较好的介孔结构, 表现了更高的光催化降解邻苯二甲酸二甲酯的活性. 其活性提高的主要原因是N/TiO2含有更高浓度的氮和对可见光具有更强的吸收能力.

Three-dimensionally ordered macroporous LaFeO3 perovskites exhibit better performance for chemical-looping reforming of methane than LaFeO3 nano-particles because of their unique properties including high porosity and high specific surface area.Figure optionsDownload as PowerPoint slide