Integrated operando X-ray absorption and DFT characterization of Cu-SSZ-13 exchange sites during the selective catalytic reduction of NOx with NH3
Integrated operando X-ray absorption and DFT characterization of Cu-SSZ-13 exchange sites during the selective catalytic reduction of NOx with NH3
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DOI：
10.1016/j.cattod.2011.11.037
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发表时间：
2012-04-30
期刊：
影响因子：
5.3
通讯作者：
Ribeiro, F. H.
中科院分区：
文献类型：
--
作者：
McEwen, J. -S.;Anggara, T.;Ribeiro, F. H.
采用X射线吸收光谱（XAS）、密度泛函理论（DFT）和第一性原理热力学模型相结合的方法，研究了在氨选择性催化还原（SCR）过程中，铜交换菱沸石（Cu-SSZ-13）中铜的氧化态和配位环境.四重配位Cu（II）被发现在所谓的快速和慢速SCR条件下主导所制备的Cu-SSZ-13和Cu-SSZ-13，其中NO2/NOx比分别为0.5和1。在标准SCR条件下，在进料中不含NO2，观察到混合的Cu（I）和Cu（II）氧化态，沿着平均Cu配位的减少。发现每摩尔的速率对于快SCR条件和慢SCR条件大约相等，并且对于标准条件小两倍。定期DFT计算用于确定的结构，氧化态，和相对稳定的铜离子电荷补偿与一个或两个铝和extralattice氧，羟基和水配体。发现与H2O或OH结合的2倍Cu（I）和4倍Cu（II）物种在宽范围的条件下是最稳定的。使用NO2/NO比率作为反应氧化强度的替代物提供了与在标准SCR条件下观察到的Cu（I）物质的外观的良好一致性。结果强调了铜氧化还原化学在SCR催化中的作用。(C)2011 Elsevier B. V.保留所有权利。
We investigate the Cu oxidation state and coordination environment in copper-exchanged chabazite (Cu-SSZ-13) under operando conditions representative of NOx selective catalytic reduction (SCR) with ammonia, using a combination of X-ray absorption spectroscopy (XAS) experiments, density functional theory (DFT), and first-principles thermodynamics models. Four-fold-coordinated Cu(II) are found to dominate the as-prepared Cu-SSZ-13 and Cu-SSZ-13 under so-called Fast and Slow SCR conditions, in which the NO2/NOx ratios are 0.5 and 1, respectively. Under Standard SCR conditions, containing no NO2 in the feed, mixed Cu(I) and Cu(II) oxidation states are observed along with a reduction in the average Cu coordination. The rate per mole was found to be about equal for Fast and Slow SCR conditions and a factor of two less for Standard conditions. Periodic DFT calculations are used to determine the structure, oxidation state, and relative stability of Cu ions charge compensated with one or two Al and with extralattice oxy, hydroxy, and water ligands. Two-fold Cu(I) and 4-fold Cu(II) species bound with H2O or OH are found to be most stable over a wide range of conditions. Using the NO2/NO ratio as a surrogate for the reaction oxidation strength provides good agreement with the observed appearance of Cu(I) species under Standard SCR conditions. The results highlight the role of Cu redox chemistry in SCR catalysis. (C) 2011 Elsevier B.V. All rights reserved.