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Methane Combustion over Lanthanum-based Perovskite Mixed Oxides

博士研究生：Hamid (哈米德）

指导教师：李俊华教授

所属院系：环境学院

论文摘要

    Three-dimensionally ordered macroporoous (3DOM) and nanostructured catalysts are more and more important for highly developed applications relating in photonic crystals, catalysis, and membrane separation. Recent theoretical and experimental studies have recommended that noble metals supported on perovskite-type oxides (ABO3) with well-ordered porous networks show promising redox properties. 3DOM structure-supported noble metals have shown great potential for broad applications due to their interesting properties (e.g., high BET and ordered mesostructures). Although the macroporous metals (voids >50 nm) have been widely achieved, the fabrication of ordered macroporous perovskites with mesoporous skeletons is still challenging. The main innovations results are as follows:

    In this work, 1D single-crystalline nanowires of perovskite-type oxides (PTOs) La0.5Sr0.5CoO3 were firstly prepared by a dextrose-assisted hydrothermal route (DHR) and/or l-Lysine. It is found that the single-crystalline sample (LSCO-2) derived at temperature of 170°C with a dextrose/l-Lysine volumetric ratio of 0.3/1.0 of new nanowire DHR possessed the high surface O2 concentration and the best low-temperature reducibility, and the high BET surface area (17.7 m2g−1), which exhibited much better than that conventional process for polycrystalline La0.5Sr0.5CoO3 catalyst. After running at 800°C for 50h, the nanowire DHR (LSCO-2) showed a higher stability and activity than the nanoparticles (LSCO-4) counterpart. It is believed that the good catalytic performance of LSCO-2 was related to factors such as higher surface area/energies, and better low-temperature reducibility, as well as to the different adsorbed O2 species concentration.

    In addition, three-dimensionally ordered macroporous rhombohedral La0.6Sr0.4MnO3 (3DOM LSMO) with nanovoids were synthesized using polymethyl methacrylate (PMMA) microspheres as hard template and dimethoxytetraethylene glycol (DMOTEG), ethylene glycol, polyethylene glycol (PEG400), L-lysine or triblock copolymer (Pluronic P123) as surfactant. It is found that LSMO-DP3 sample derived with 3.0 mL of DMOTEG and 5.0 mL of PEG400 possessed the higher O2 species concentration and BET and better low-temperature reducibility, and hence exhibiting a good catalytic activity for combustion of CH4. The apparent activation energies of the 3DOM LSMO samples were estimated to be 56.5–75.2 kJ/mol, with the LSMO-DP3 sample showing the lowest apparent activation energy (56.6 kJ/mol).

    Highly dispersed Ag NPs supported on high-surface-area 3DOM La0.6Sr0.4MnO3 (yAg/3DOM La0.6Sr0.4MnO3; y = 0, 1.57, 3.63, and 5.71 wt%) were successfully generated with high surface areas (38.2–42.7 m2/g) via the dimethoxytetraethylene glycol-assisted gas bubbling reduction method. Meanwhile, the effects of H2O and SO2 on the catalytic activity of the 3.63 wt% Ag/3DOM La0.6Sr0.4MnO3 sample were also examined.

    It is concluded that its super catalytic activity was associated with its highest oxygen adspecies concentration, good low-temperature reducibility, larger surface area, and strong interaction between metal and support as well as unique nanovoid-walled 3DOM structure.