The interaction of reactants, intermediates and products with Cu ions in Cu-SSZ-13 NH 3 SCR catalysts: an energetic and ab initio X-ray absorption modeling study
The interaction of reactants, intermediates and products with Cu ions in Cu-SSZ-13 NH 3 SCR catalysts: an energetic and ab initio X-ray absorption modeling study
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Cu-SSZ-13 NH 3 SCR 催化剂中反应物、中间体和产物与铜离子的相互作用：能量从头算 X 射线吸收模型研究
DOI：
10.1039/c5cy02252e
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
McEwen, Jean-Sabin
中科院分区：
文献类型：
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作者：
Zhang, Renqin;Szanyi, János;Gao, Feng;McEwen, Jean-Sabin
在这篇文章中，研究了具有单电荷补偿铝原子（ZCu）且 Si : Al 比为 11 : 1 的 Cu-SSZ-13 中 Cu 最可能的位置，包括使用基于密度泛函理论的第一原理计算在 NH3 SCR 反应中发现的反应物、中间体和产物的吸附效应。对于普通 ZCu，6 元环 (6MR) 位点在能量上最有利，而 8 元环 (8MR) 位点的能量较差，与 6MR 位点相比，能量差异约为 0.5 eV。分子吸附后，8MR 和 6MR 位点中 Cu 之间的能量差异减小，在某些情况下几乎消失。对于NO或CO吸附的复杂情况，2个NO或2个CO分子的共吸附，以及NO或CO与OH和H2O的共吸附，削弱了吸附物与Cu之间的相互作用。不同条件下 Cu-SSZ-13 中 Cu 的 X 射线吸收近边缘结构 (XANES) 也根据第一原理进行了建模。在 Cu 的 K 边缘 XANES 中发现了约 8979.5 eV 的小峰特征，表明 Cu 在 8MR 位点具有干净的 ZCu 构象，而当 Cu 在 6MR 位点时则不存在该特征。我们通过分析 Cu 激发态的相应 PDOS，同时考虑芯空穴效应，将这种情况以及其他代表性构型的结果关联起来。 6MR 或 8MR 位点中 Cu 的分子吸附会产生与其位置无关的 Cu K 边缘 XANES。当 NO（或 CO、N2）吸附到 ZCu 中的 Cu 上时，K 边缘 XANES 中出现 8980 eV 处的小峰特征，这是由 Cu 4p 态分裂引起的。在孤立的 Cu 离子上存在两种共吸附物质的情况下对 XANES 的分析表明，Cu 的 K 边缘位置具有以下顺序（从低能到高能）：clean < M < M + H2O < 2M < M + OH（M 表示 NO 或 CO）。因此，我们得出结论：(1) XANES 可以很容易地区分 ZCu 上的吸附物，因为它们的氧化能力不同，但 (2) XANES 不能用于区分吸附物存在下的 Cu 位置和氧化态，除非存在 H2O 和 NH3 时可以进行这种区分。
In this contribution, the most likely positions for Cu in Cu-SSZ-13 with a single charge compensating Al atom (ZCu) with a Si : Al ratio of 11 : 1 were investigated, including the effect of the adsorption of reactants, intermediates, and products that one would find in an NH3 SCR reaction by using first-principles calculations based on density functional theory. The 6-membered ring (6MR) site is the most energetically favorable, while the 8-membered ring (8MR) sites are less favorable with energy differences of about 0.5 eV with respect to the 6MR site for plain ZCu. Upon molecular adsorption, the energy differences between Cu in the 8MR and 6MR sites decrease and, in some cases, almost disappear. For the complex scenarios of NO or CO adsorption, the co-adsorption of 2 NO or 2 CO molecules, as well as NO or CO with OH and H2O, weakens the interaction between adsorbates and Cu. The X-ray absorption near edge structure (XANES) of Cu in Cu-SSZ-13 under different conditions was also modeled from first principles. A small peak feature around 8979.5 eV was found in the K-edge XANES of Cu for a clean ZCu conformation with Cu in the 8MR site, while this feature is absent when Cu is in the 6MR site. We correlate this result for this case as well as for other representative configurations by analyzing the corresponding PDOS of the excited state of Cu while taking into account the core-hole effect. Molecular adsorption onto Cu in the 6MR or 8MR site results in a Cu K-edge XANES that is independent of its location. When NO (or CO, N2) is adsorbed onto Cu in ZCu, a small peak feature in the K-edge XANES appears at 8980 eV, which is induced by the splitting of the Cu 4p state. An analysis of the XANES in the presence of two co-adsorbed species on an isolated Cu ion shows that the K-edge position of Cu has the following order (from low to high energy): clean < M < M + H2O < 2M < M + OH (M denotes NO or CO). As a result, we conclude that (1) XANES can readily distinguish between adsorbates on ZCu due to their different oxidizing capacities, but (2) XANES cannot be used to distinguish between the Cu location and the oxidation state in the presence of adsorbates, except in the presence of H2O and NH3 where such distinctions can be made.