Mechanistic insights into the oxidation of copper(i) species during NH3-SCR over Cu-CHA zeolites: a DFT study
Mechanistic insights into the oxidation of copper(i) species during NH3-SCR over Cu-CHA zeolites: a DFT study
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DOI：
10.1039/d0cy00379d
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发表时间：
2020-06-07
影响因子：
5
通讯作者：
Shimizu, Ken-ichi
中科院分区：
文献类型：
--
作者：
Liu, Chong;Kubota, Hiroe;Shimizu, Ken-ichi
使用氨 (NH3-SCR) 在 Cu 交换沸石上选择性催化还原氮氧化物，通过将 Cu(ii) 还原为 Cu(i) 以及随后将 Cu(i) 再氧化为 Cu(ii) 进行。尽管还原半循环机制已经相对完善，但 Cu(i) 形成原始 Cu(ii) 物种的再氧化途径非常复杂且仍不清楚。在此，通过定期 DFT 计算研究了 NH3-SCR 过程中 CHA 沸石中 Cu(i) 到 Cu(ii) 物质的氧化机制。 NH3 溶剂化的 Cu(i) 和 Cu(ii) 物种被考虑用于探索氧化活化反应途径。结果表明，以 O-2 作为唯一氧化剂，Cu(i) 可以通过具有中等反应势垒的多核 Cu-oxo 中间体有效氧化为 Cu(ii)。研究发现，NO 辅助的 Cu(i) 氧化有利于硝酸铜/亚硝酸铜物质的形成，这些物质似乎仅充当非循环静止状态。我们认为，在标准 NH3-SCR 条件下，以 O-2 作为唯一氧化剂将 Cu(i) 重新氧化为 Cu(ii) 在氧化半循环中起着关键作用。
Selective catalytic reduction of nitrogen oxides using ammonia (NH3-SCR) over Cu-exchanged zeolites 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. Herein, 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 O-2 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 O-2 as the sole oxidant plays a key role in the oxidation half cycle under standard NH3-SCR conditions.