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

在Cu交换的沸石上使用氨（NH3-SCR）选择性催化还原氮氧化物是一个重要的过程，并且通过将Cu（II）还原成Cu（I）和随后将Cu（I）再氧化成Cu（II）来进行。虽然还原半循环的机制已经相对较好地建立，但Cu（I）再氧化形成原始Cu（II）物种的途径是高度复杂的，并且仍然不清楚。在我们的研究中，铜（I）到铜（II）物种在CHA沸石NH3-SCR过程中的氧化机理进行了定期DFT计算研究。NH3-溶剂化的Cu（I）和Cu（II）物种被认为是探索氧化活化反应途径。结果表明，以O2为唯一氧化剂时，Cu（I）可以通过多核Cu-氧代中间体有效地氧化为Cu（II），反应势垒适中.发现NO辅助的Cu（I）的氧化有利于形成硝酸铜/亚硝酸铜物种，其似乎仅作为关闭循环的静息状态。我们建议，再氧化的Cu（I）的Cu（II）与O2作为唯一的氧化剂起着关键作用的氧化半周期在标准的NH3-SCR条件下。这些信息对阳离子交换沸石催化过程的研究具有重要意义。

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.