Abstract:
Three-dimensionally ordered macroporous (3DOM) LaFe
0.7Co
0.3O
3 perovskite-type oxides were synthesized using a polystyrene (PS) colloidal crystal templating method. The obtained 3DOM LaFe
0.7Co
0.3O
3 perovskites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauere-Emmette-Teller (BET) surface area. Its performance as oxygen carriers in chemical looping steam methane reforming (CL-SMR) to produce syngas (H
2 + CO) and hydrogen were investigated in a fixed-bed reactor. The size of PS spheres obviously increases as the styrene addition increases. The calcination temperature is the major factor to affect the prepared 3DOM perovskite. SEM and TEM analysis show that the samples calcined at 500, 800 and 850℃ exhibit good 3DOM structures which collapse when the sample is calcined at 900℃. XRD results suggest that the obtained 3DOM LaFe
0.7Co
0.3O
3 perovskites are pure crystalline. Two kinds of oxygen species, bulk lattice oxygen and surface adsorbed oxygen, are found to exist on the 3DOM LaFe
0.7Co
0.3O
3 perovskites. The surface oxygen contributes to the complete oxidization of methane to CO
2 and H
2O in beginning of the reaction, while the bulk lattice oxygen tends towards partial methane oxidation to H
2 and CO. In the methane conversion step, methane is partially oxidized into syngas at a H
2/CO mol ratio close to 2:1 by the 3DOM- LaFe
0.7Co
0.3O
3 in a wide range of the reactions, suggesting that the sample exhibits a good resistance to carbon deposition. In the steam oxidation step, the reduced perovskites are oxidized by steam to generate hydrogen with hydrogen productivity about 4 mmol/g oxygen carriers.