School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin, China; Tianjin Key Laboratory of Clean Energy and Pollution Control, Hebei University of Technology, Tianjin, China.
School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin, China; Tianjin Key Laboratory of Clean Energy and Pollution Control, Hebei University of Technology, Tianjin, China.
Sci Total Environ. 2021 Apr 10;764:142805. doi: 10.1016/j.scitotenv.2020.142805. Epub 2020 Oct 8.
Volatile organic compounds (VOCs) emitted from coal-fired flue gas of thermal power plants have reached unprecedented levels due to lack of understanding of reaction mechanisms under industrial settings. Herein, inhibition mechanisms for catalytic oxidation of o-xylene in simulated coal-fired flue gas are elucidated with in-situ and ex-situ spectroscopic techniques considering the presence of impurity components (NO, NH, SO, HO). MnCe oxide catalysts prepared at Mn: Ce mass ratios of 6:4 are demonstrated to promote 87% o-xylene oxidation at 250 °C under gas hourly space velocities of 60,000 h. Reaction intermediates on the catalyst surface are revealed to be o-benzoquinones, benzoates, and formate and they were stably formed under O/N atmospheres. When either NO or NH was introduced into the simulated flue gas, the formed species shifted toward formate in minutes, which indicated that changes in catalyst surface chemistry are directly related to impurity components. Presence of NH in the simulated flue gas inhibited o-xylene oxidation by reducing Mn and lowering Brønsted acidity of the catalyst. Impurity components associated with pollutant removal processes (Hg oxidation and selective catalytic reduction of NO) lowered o-xylene removal efficiency. Presence of o-xylene in the flue gas had little effect on the efficiency of pollutant removal processes. Layered catalytic beds located downstream from Hg/NO pollutant removal processes are proposed to lower VOC emissions from coal-fired flue gases of thermal power plants in industrial settings.
由于缺乏对工业环境下反应机制的理解，来自火力发电厂燃煤烟道气的挥发性有机化合物（VOCs）已经达到了前所未有的水平。在此，通过原位和异位光谱技术，考虑到杂质成分（NO、NH、SO、HO）的存在，阐明了模拟燃煤烟道气中邻二甲苯催化氧化的抑制机制。结果表明，在气相时空速度为 60000 h 的条件下，Mn:Ce 质量比为 6:4 的 MnCe 氧化物催化剂在 250°C 时可促进 87%的邻二甲苯氧化。在催化剂表面上揭示了反应中间体为邻苯醌、苯酸盐和甲酸盐，并且在 O/N 气氛下它们稳定形成。当向模拟烟道气中引入 NO 或 NH 时，形成的物质在几分钟内转变为甲酸盐，这表明催化剂表面化学性质的变化与杂质成分直接相关。模拟烟道气中 NH 的存在通过降低 Mn 和降低催化剂的 Brønsted 酸度来抑制邻二甲苯的氧化。与污染物去除过程（Hg 氧化和选择性催化还原 NO）相关的杂质成分降低了邻二甲苯的去除效率。烟道气中存在邻二甲苯对污染物去除过程的效率几乎没有影响。建议在 Hg/NO 污染物去除过程的下游设置层状催化床，以降低火力发电厂燃煤烟道气中的 VOC 排放。
