Development in Process of Direct Decomposition of Nitrogen Monoxide over Copper Ion-exchanged Zeolite Catalysts

提出了铜离子交换沸石催化剂上NO的直接分解和选择性还原作为脱除NO的新方法，铜离子交换ZSM-5沸石（Cu-Z）对NO的分解活性最高，且Cu-Z沸石的活性随交换程度的增加而增加。通过使用乙酸铜（II）水溶液或向硝酸铜（II）水溶液中加入氨重复离子交换ZSM-5沸石而制备的铜离子交换水平为100%或更高的沸石，即使在氧存在下和在高GHSV区域也显示出显著高的活性。用IR、ESR、磷光、TPD和CO吸附等方法对Cu-Z进行了研究，结果表明：（1）交换到沸石中的Cu^2+离子经高温抽真空后被还原为Cu^+和/或Cu^+-Cu^+;（2）在773 K下暴露于氧气中并随后抽真空后，沸石中约40%的铜离子被还原为Cu^+和/或Cu^+-Cu^+; 关于我们 沸石以Cu^+离子形式存在，（3）NO在Cu^+上吸附形成的NO^-物种是NO分解的中间体，（4）沸石中Cu^+<@2<@>D2 <@D1>@> D1 Cu <@D12+@>D1的氧化还原循环可能是实现分解反应的关键步骤。本文首次发现了在氧气存在下烃类对NO的选择性还原，Cu-Z在473-573 K的低温下对NO的脱除效果显著。在NO+C<@D23@> D2 H <@D26@>D2+O<@D22@> D2体系中，SO<@D22 @> D2的加入并不严重影响该选择性还原反应的活性。在SO<@D22 @> D2存在下，NO的转化率由不存在SO <@D22 @> D2时的100%提高到85%（773 K），这与加入相同量的SO<@D22 @> D2时NO直接分解的催化活性完全丧失的事实相反.此外，Cu-Z在525 K下的还原速率分别高于H-沸石和氧化铝催化剂在673和773 K下的还原速率，这两种催化剂据报道是活性的。少

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-exchange 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 Cu^<2+> ions exchanged into zeolite were reduced to Cu^+ and/or Cu^+-Cu^+ through evacuation at elevated temperature, (2) after exposure to oxygen at 773 K and subsequent evacuation, about 40% copper ions in zeo … More lite 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^+<@2<@>D2 <@D1>@>D1Cu<@D12+@>D1 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 473-573 K. The activity for this selective reduction in NO+C<@D23@>D2H<@D26@>D2+O<@D22@>D2 system was not poisoned very much by addition of SO<@D22@>D2. The conversion into N<@D22@>D2 was changed to 85% (773 K) in the presence of SO<@D22@>D2, from 100% in the absence of SO<@D22@>D2, which is in contrast with the fact that the catalytic activity for direct decomposition of NO was completely lost on adding the same amount of SO<@D22@>D2. Furthermore, the reduction rate over Cu-Z at 525 K was higher than those over H-zeolite and alumina catalysts at 673 and 773 K, respectively, which have been reported to be active, after findings by the authors. Less