Determining Cu–Speciation in the Cu–CHA Zeolite Catalyst: The Potential of Multivariate Curve Resolution Analysis of In Situ XAS Data
Determining Cu–Speciation in the Cu–CHA Zeolite Catalyst: The Potential of Multivariate Curve Resolution Analysis of In Situ XAS Data
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DOI：
10.1007/s11244-018-1036-9
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发表时间：
2018-08
影响因子：
3.6
通讯作者：
Andrea Martini;Andrea Martini;Eugenio Alladio;E. Borfecchia
中科院分区：
文献类型：
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作者：
Andrea Martini;Andrea Martini;Eugenio Alladio;E. Borfecchia
Cu-CHA分子筛是一种极具吸引力的平台，可用于设计NH3辅助选择性催化还原（NH3-SCR）脱氮催化剂和低温甲烷选择性氧化制甲醇（MTM）催化剂。对这种材料中铜形态的定量理解是揭示这些高影响工艺的结构-性能关系的关键一步。在这里，我们选择铜-CHA作为案例研究，以证明化学计量学方法的潜力，如多变量曲线分辨率（MCR）与主成分分析（PCA）相结合。我们采用这些方法来协助解释X射线吸收光谱（XAS）实验在近边缘（XANES）区域，确定光谱特征和浓度分布的纯铜物种形成。我们查明的组成对材料还原率的影响，并强调铜形态的MTM过程的生产率的关系。此外，我们还报告了关于Cu-CHA中O2衍生物质形成的新见解，这些见解是通过MCR分析在He和O2气流中对Cu-CHA进行热处理期间收集的高能量分辨率荧光检测（HERFD）XANES数据获得的。多变量分析，结合所采用的上级能量分辨率，使我们能够确定一个额外的Cu（II）物种。该组件，不同于先前表征的Z[Cu（II）OH]部分，仅在O2中以显著浓度形成，并且设想在MTM转化中发挥重要作用。
The Cu–CHA zeolite today represents an attractive platform to design catalysts for deNOxapplications by NH3-assisted selective catalytic reduction (NH3–SCR) and for the low-temperature selective oxidation of methane to methanol (MTM). Accessing a quantitative understanding of Cu–speciation in this material is a key step to unveil structure–performance relationships for these high-impact processes. Herein, we select Cu–CHA as a case study to demonstrate the potential of chemometric approaches, such as multivariate curve resolution (MCR) applied in combination with principal component analysis (PCA). We employ these methods to assist the interpretation of X-ray absorption spectroscopy (XAS) experiments in the near-edge (XANES) region, determining the spectroscopic signatures and concentration profiles of the pure Cu–species formed. We pinpoint the composition impact on the material reducibility and highlight Cu–speciation–productivity relationships for the MTM process. Furthermore, we report novel insights on the formation of O2-derived species in Cu–CHA, obtained from MCR analysis of high energy resolution fluorescence detected (HERFD) XANES data collected during thermal treatment of Cu–CHA in both He and O2gas flow. Multivariate analysis, in combination with the superior energy resolution adopted, allows us to identify an additional Cu(II) species. This component, different from the previously characterized Z[Cu(II)OH] moiety, is only formed at significant concentrations in O2and it is envisaged to play an important role in the MTM conversion.