Reaction mechanism and kinetics of NOx reduction by methane on In/ZSM-5 under lean conditions
Reaction mechanism and kinetics of NOx reduction by methane on In/ZSM-5 under lean conditions
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DOI：
10.1016/j.apcatb.2005.10.016
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发表时间：
2006-04-18
影响因子：
22.1
通讯作者：
Hamada, H
中科院分区：
文献类型：
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作者：
Maunula, T;Ahola, J;Hamada, H
研究人员研究了负载在 ZSM-5 上的铟作为一种有前途的催化剂，用于在稀薄条件下通过甲烷还原 NO。质子化 H-ZSM-5 上的铟在干燥条件下表现出较高的活性，而通过离子交换制备的高负载量 7.3% 的非质子化 ZSM-5 上的铟在 8% 水存在下具有较高的活性。饲料中的NO2促进了甲烷的氧化和NO的还原。原位 FTIR 分析揭示了 In/ZSM-5 上存在较低温度下的抑制化合物和许多碳质表面化合物。在反应引发条件下，含氮碳化合物和任何吸附物质的表面覆盖率较低。有人提出，NO、部分氧化的甲烷表面衍生物和含有N-C或N-H键的实际表面还原剂的形成对于NO还原至关重要。沸石内 InO+ 被认为是 NO 还原的活性催化位点。 XRD和XPS检测到游离的In2O3可能对反应有促进作用。通过改变反应物浓度、空速和温度的 NO-CH4-O-2 实验，导出了 In/ZSM-5 催化剂的微观动力学模型，包括表面中间体。 NO2 和部分氧化的甲烷反应中形成的吸附的 H2NCO 中间体被认为在反应机理和动力学方程中充当实际的 NO 还原剂。该模型能够跟踪测量的响应，并在通常的稳态贫油条件下定量预测 NO-CH4-O-2 反应的动态性能。模拟反应条件下，吸附氧和 NO2 在活性位点上存在较高的覆盖度。在不同的未测量条件下，气体和吸附的化合物被模拟为反应器长度的函数，该模拟可以用作催化剂反应器设计的工具。 (c) 2005 Elsevier B.V. 保留所有权利。
Indium supported on ZSM-5 was investigated as a promising catalyst for NO, reduction by methane under lean conditions. Indium on protonated H-ZSM-5 showed a higher activity in dry conditions while indium on unprotonated ZSM-5 with a high loading of 7.3% prepared by ion exchange had a higher activity in the presence of 8% water. NO2 in feed promoted the methane oxidation and NO, reduction. In situ FTIR analysis revealed on In/ZSM-5 the presence of inhibiting compounds at lower temperatures and many carbonaceous surface compounds. In the reaction initiation conditions, the surface coverage of nitrogen containing carbonaccous compounds and any adsorbed species were low. It is proposed that the formation of NO,, partially oxidized methane surface derivatives and actual surface reductants containing N-C or N-H bondings are crucial in NO reduction. Intrazeolitic InO+ was proposed to be the active catalytic site in NO reduction. Free In2O3, detected by XRD and XPS, has possibly a promoting effect on the reactions. A micro kinetic model, including the surface intermediates, was derived for an In/ZSM-5 catalyst by the NO-CH4-O-2 experiments where the reactant concentrations, space velocity and temperature were varied. The adsorbed H2NCO intermediate, formed in the reaction between NO2 and partially oxidized methane, was proposed to act as an actual NO reductant in the reaction mechanism and kinetic equations. The model was able to follow measured responses and predict the dynamic performance in NO-CH4-O-2 reactions quantitatively in usual steady state lean conditions. Adsorbed oxygen and NO2 were simulated to exist with higher coverage on active sites in reaction conditions. Gas and adsorbed compounds were simulated as a function of reactor length in different unmeasured conditions, which simulations can be used as a tool in catalyst reactor design. (c) 2005 Elsevier B.V. All rights reserved.