Three-dimensionally ordered macroporous LaFeO_3 perovskites for chemical-looping steam reforming of methane

摘要

Three-dimensionally ordered macroporous (3DOM) LaFeO_3 and nano-LaFeO_3 perovskite-type oxides were synthesized by impregnation of polystyrene (PS) templates and combustion method, respectively. The obtained LaFeO_3 perovskites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, and hydrogen-temperature programmed reduction (H_2-TPR). The performance of the perovskites as oxygen carriers in chemical looping steam methane reforming (CL-SMR) to produce syngas (H_2 + CO) and hydrogen were investigated. The synthesized 3DOM-LaFeO_3 was pure crystalline perovskite giving a surface area of 8.088 m~2/g, higher than that of nano-LaFeO_3 particles (4.323 m~2/g). In the methane reduction stage, methane was partially oxidized into syngas at a H_2/CO molar ratio close to 2:1 by the 3DOM-LaFeO_3 in the main stage of the reactions. In the steam oxidation stage, the reduced perovskites were oxidized by steam to generate hydrogen simultaneously. No significant decrease of the yields of syngas and hydrogen was observed during ten successive redox cycles, indicating that the 3DOM-LaFeO_3 perovskites have good repeatability. In comparison to nano-LaFeO_3, 3DOM-LaFeO_3 has more stable reactivity of methane oxidation and better resistance to carbon formation. In spite of a part of 3DOM structure were collapsed in the course of the cyclic reactions, the specific surface area of the 3DOM-LaFeO_3 was still higher than that of the nano one. The better reactivity of 3DOM-LaFeO_3 compared with that of nano-LaFeO_3 is partially attributed to the higher surface area.