Cu/Zeolites catalyze selective catalytic reduction of nitric oxide with ammonia. Although the progress has been made in understanding the rate-limiting step of reaction which is reoxidation of Cu(I)(NH3)2 with oxygen to restore the catalytically active Cu(II) site, the exact NO reduction chemistry remained unknown. Herein, we show that nitrosyl ions NO+ in the zeolitic micropores are the true active sites for NO reduction. They react with ammonia even at below/room temperature producing molecular nitrogen through the intermediacy of N2H+ cation. Isotopic experiments confirm our findings. No copper is needed for this reaction to occur. However, when NO+ reacts, “freed up” Bronsted acid site gets occupied by NH3 to form NH4+ – and so the catalytic cycle stops because NO+ does not form on NH4-Zeolites due to their acid sites being already occupied. Therefore, the role of Cu(II) in Cu/Zeolite catalysts is to produce NO+ by the reaction: Cu(II) + NO à Cu(I) + NO+ which we further confirm spectroscopically. The NO+ then reacts with ammonia to produce nitrogen and water. Furthermore, when Cu(I) gets re-oxidized the catalytic cycle then can continue. Thus, our findings are critical for understanding complete SCR mechanism.

中文翻译：

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分子筛催化剂上氨（SCR）还原NO的机理研究

铜/沸石催化氨选择性氧化还原一氧化氮。尽管在了解反应的限速步骤方面已经取得了进展，该步骤是用氧气将Cu（I）（NH3）2再氧化以恢复催化活性的Cu（II）位，但确切的NO还原化学仍然未知。在本文中，我们表明沸石微孔中的亚硝酰基离子NO +是还原NO的真正活性位点。它们甚至在低于/室温的条件下也与氨反应，通过N2H +阳离子产生氨氮。同位素实验证实了我们的发现。发生反应不需要铜。但是，当NO +反应时，“释放”的布朗斯台德酸位被NH3占据，形成NH4 + –因此，由于NH4沸石上的酸位已经被占用，因此没有在NH4-沸石上形成NO +，因此催化循环停止。因此，Cu（II）在Cu /沸石催化剂中的作用是通过以下反应生成NO +：Cu（II）+ NO→Cu（I）+ NO +，我们在光谱上进一步证实了这一点。然后，NO +与氨反应生成氮气和水。此外，当Cu（I）被重新氧化时，催化循环便可以继续进行。因此，我们的发现对于理解完整的SCR机制至关重要。