Removal of Nitrogen Monoxide over Copper Ion-exchanged Zeolite Catalysts
Removal of Nitrogen Monoxide over Copper Ion-exchanged Zeolite Catalysts
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铜离子交换沸石催化剂去除一氧化氮
DOI：
10.1627/jpi1958.34.375
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发表时间：
1991
影响因子：
1
通讯作者：
H. Yahiro
中科院分区：
文献类型：
--
作者：
M. Iwamoto;N. Mizuno;H. Yahiro
提出了在铜离子交换沸石催化剂上直接分解和选择性还原一氧化氮作为去除 NO 的新方法。铜离子交换ZSM-5沸石(Cu-Z)是分解NO最活跃的催化剂。 Cu-Z沸石的活性随着交换水平的增加而增加。通过使用乙酸铜(II)水溶液重复进行ZSM-5沸石的离子交换或向硝酸铜(II)水溶液中添加氨来制备铜离子交换水平为100%或更高的沸石，即使在氧气存在和高GHSV区域下也表现出显着的高活性。通过IR、ESR、磷光、TPD和CO吸附测量，澄清了Cu-Z：(1)交换到沸石中的Cu2+离子通过高温抽真空被还原为Cu+和/或Cu+-Cu+，(2)在773K暴露于氧气并随后抽真空后，沸石中约40%的铜离子以Cu+离子的形式存在，(3)吸附NO形成的NO-物种Cu+上的Cu+将成为NO分解的中间体，并且(4)沸石中Cu+_??_Cu2+的氧化还原循环可能是实现分解反应的关键步骤。作者首先发现了在氧气存在的情况下碳氢化合物选择性还原 NO，并且 Cu-Z 在低至 523-673K 的温度下对于去除 NO 非常有效。 NO+C3H6+O2 系统中这种选择性还原的活性并没有因为添加 SO2 而受到很大的毒害。在 SO2 存在下，N2 转化率从不存在 SO2 时的 100% 变为 85% (773K)，这与添加等量 SO2 时直接分解 NO 的催化活性完全丧失的事实形成对比。此外，根据作者的研究结果，Cu-Z 在 573K 时的还原率分别高于 H-沸石和氧化铝催化剂在 723 和 773K 时的还原率，据报道这两种催化剂具有活性。
Direct decomposition and selective reduction of nitrogen monoxide over copper ion-exchanged zeolite catalysts are proposed as new methods for removal of NO. The copper ion-exchanged ZSM-5 zeolite (Cu-Z) was the most active catalyst for decomposition of NO. The activity of Cu-Z zeolites increased with increase in the exchange level. The zeolites with copper ion-excange levels of 100% or more, which could be prepared by repeating ion exchange of the ZSM-5 zeolite using aqueous copper(II) acetate solution or addition of ammonia into the aqueous copper(II) nitrate solution, showed significantly high activity even in the presence of oxygen and at high GHSV region. It was clarified concerning Cu-Z, by using IR, ESR, phosphorescence, TPD, and CO adsorption measurements that (1) the Cu2+ ions exchanged into zeolite were reduced to Cu+ and/or Cu+-Cu+ through evacuation at elevated temperature, (2) after exposure to oxygen at 773K and subsequent evacuation, about 40% copper ions in zeolite existed as Cu+ ions, (3) the NO- species formed by adsorption of NO on Cu+ would be an intermediate in the NO decomposition, and (4) redox cycle of Cu+_??_Cu2+ in the zeolite is probably a key step to achieve the decomposition reaction. Selective reduction of NO by hydrocarbon in the presence of oxygen was first found by the authors and Cu-Z was remarkably effective for NO removal at temperatures as low as 523-673K. The activity for this selective reduction in NO+C3H6+O2 system was not poisoned very much by addition of SO2. The conversion into N2 was changed to 85% (773K) in the presence of SO2, from 100% in the absence of SO2, which is in contrast with the fact that the catalytic activity for direct decomposition NO was completely lost on adding the same amount of SO2. Furthermore, the reduction rate over Cu-Z at 573K was higher than those over H-zeolite and alumina catalysts at 723 and 773K, respectively, which have been reported to be active, after findings by the authors.