Formation of [Cu2O2]2+ and [Cu2O]2+ toward C–H Bond Activation in Cu-SSZ-13 and Cu-SSZ-39,ACS Catalysis

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Formation of [Cu2O2]2+ and [Cu2O]2+ toward C–H Bond Activation in Cu-SSZ-13 and Cu-SSZ-39
ACS Catalysis ( IF 11.3 ) Pub Date : 2017-05-18 00:00:00 , DOI: 10.1021/acscatal.6b03005
Bahar Ipek , Matthew J. Wulfers , Hacksung Kim _{1,

2} , Florian Göltl , Ive Hermans , Joseph P. Smith , Karl S. Booksh , Craig M. Brown ₃ , Raul F. Lobo

Affiliation

Cu-exchanged small-pore zeolites (CHA and AEI) form methanol from methane (>95% selectivity) using a 3-step cyclic procedure (Wulfers et al. Chem. Commun. 2015, 51, 4447−4450) with methanol amounts higher than Cu-ZSM-5 and Cu-mordenite on a per gram and per Cu basis. Here, the Cu_xO_y species formed on Cu-SSZ-13 and Cu-SSZ-39 following O₂ or He activation at 450 °C are identified as trans-μ-1,2-peroxo dicopper(II) ([Cu₂O₂]²⁺) and mono-(μ-oxo) dicopper(II) ([Cu₂O]²⁺) using synchrotron X-ray diffraction, in situ UV–vis, and Raman spectroscopy and theory. [Cu₂O₂]²⁺ and [Cu₂O]²⁺ formed on Cu-SSZ-13 showed ligand-to-metal charge transfer (LMCT) energies between 22,200 and 35,000 cm^–1, Cu–O vibrations at 360, 510, 580, and 617 cm^–1 and an O–O vibration at 837 cm^–1. The vibrations at 360, 510, 580, and 837 cm^–1 are assigned to the trans-μ-1,2-peroxo dicopper(II) species, whereas the Cu–O vibration at 617 cm^–1 (Δ¹⁸O = 24 cm^–1) is assigned to a stretching vibration of a thermodynamically favored mono-(μ-oxo) dicopper(II) with a Cu–O–Cu angle of 95°. On the basis of the intensity loss of the broad LMCT band between 22,200 and 35,000 cm^–1 and Raman intensity loss at 571 cm^–1 upon reaction, both the trans-μ-1,2-peroxo dicopper(II) and mono-(μ-oxo) dicopper(II) species are suggested to take part in methane activation at 200 °C with the trans-μ-1,2-peroxo dicopper(II) core playing a dominant role. A relationship between the [Cu₂O_y]²⁺ concentration and Cu(II) at the eight-membered ring is observed and related to the concentration of [CuOH]⁺ suggested as an intermediate in [Cu₂O_y]²⁺ formation.

中文翻译：

[Cu ₂ O ₂ ] ²⁺和[Cu ₂ O] ²⁺在Cu-SSZ-13和Cu-SSZ-39中朝CH键活化的方向形成

铜交换的小孔分子沸石（CHA和AEI）使用三步循环程序从甲烷（> 95％的选择性）形成甲醇（Wulfers等， Chem.Commun。 2015年， 51，（4447-4450），其中甲醇的含量按每克和每铜计算高于Cu-ZSM-5和铜丝光沸石。在这里，在450°C下O ₂或He活化后，在Cu-SSZ-13和Cu-SSZ-39上形成的Cu _x O _y物种被确定为反式-μ-1,2-过氧双铜（II）（[Cu ₂ O ₂ ] ²⁺）和单-（μ-氧代）双铜（II）（[Cu ₂ O] ²⁺），使用同步加速器X射线衍射，原位UV-vis以及拉曼光谱和理论。[Cu ₂ O ₂ ] ²⁺和[Cu ₂ O] ²⁺在Cu-SSZ-13上形成的晶体显示出22,200至35,000 cm ^–1之间的配体到金属的电荷转移（LMCT）能量，在360、510、580和617 cm ^–1处的Cu–O振动以及在120 cm ^–1处的O–O振动。 837厘米^–1。在360的振动，510，580，和837厘米^-1分配给反-μ-1,2-过氧亚铜（II）物种，而在Cu-O振动在617厘米^-1（Δ ¹⁸ O = 24 cm ^–1）被分配给热力学上受欢迎的单（μ-氧代）双铜（II）的拉伸振动，其Cu–O–Cu角为95°。根据22,200至35,000 cm ^–1之间的宽LMCT波段的强度损失和571 cm处的拉曼强度损失^–1反应时，建议反式-μ-1,2-过氧双铜（II）和单-（μ-氧代）双铜（II）都参与反式-μ在200°C的甲烷活化-1,2-过氧双铜（II）核起主导作用。观察到[Cu ₂ O _y ] ²⁺浓度与八元环处的Cu（II）之间的关系，并且与[Cu ₂ O _y ] ²⁺形成中建议的中间体[CuOH] ⁺的浓度有关。。

更新日期：2017-06-28

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