実験と理論の協働によるメタン多量化反応の機構解明と触媒設計

氨（NH3-SCR）在Cu交换沸石上选择性催化还原氮氧化物是一个重要的过程，其过程是Cu（II）还原为Cu(I)，随后Cu(I)再氧化为Cu（II）。虽然还原半循环的机理已经比较完善，但Cu(I)形成原始Cu（II）的再氧化途径非常复杂，尚不清楚。采用周期DFT计算方法，研究了NH3-SCR过程中Cu(I)在CHA沸石中氧化为Cu（II）的机理。研究了nh3溶剂化Cu(I)和Cu（II）的氧化活化反应途径。结果表明，在O2为唯一氧化剂的情况下，Cu(I)可以通过反应势垒适中的多核Cu-o中间体有效氧化为Cu（II）。no辅助Cu(I)的氧化有利于Cu(I)的形成，这些Cu(I)似乎只在非循环静息状态下起作用。我们认为，在标准NH3-SCR条件下，以O2为唯一氧化剂的Cu(I)再氧化成Cu（II）在氧化半循环中起关键作用。所得信息对阳离子交换沸石上的各种催化过程具有重要意义。

Selective catalytic reduction of nitrogen oxides using ammonia (NH3-SCR) over Cu-exchanged zeolites is an important process and proceeds via reduction of Cu(II) to Cu(I) and subsequent reoxidation of Cu(I) to Cu(II). Although the mechanism of reduction half cycle has been relatively well established, reoxidation pathways of Cu(I) to form the original Cu(II) species are highly complicated and remain unclear. In our study, oxidation mechanisms of Cu(I) to Cu(II) species in CHA zeolites during the NH3-SCR process were investigated by periodic DFT calculations. The NH3-solvated Cu(I) and Cu(II) species were considered for exploring the oxidative activation reaction pathways. The results show that, with O2 as the sole oxidant, Cu(I) can be effectively oxidized to Cu(II) via multinuclear Cu-oxo intermediates with moderate reaction barriers. The NO-assisted oxidation of Cu(I) was found to favor the formation of Cu nitrate/nitrite species, which seem to only act as off-cycle resting states. We propose that reoxidation of Cu(I) to Cu(II) with O2 as the sole oxidant plays a key role in the oxidation half cycle under standard NH3-SCR conditions. The obtained information would be important for various catalytic processes over cation-exchanged zeolites.