通过 H2-TPR 和原位 EPR 研究脱水 CHA 沸石中的 Cu 形态,The Journal of Physical Chemistry C

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通过 H2-TPR 和原位 EPR 研究脱水 CHA 沸石中的 Cu 形态
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2023-06-28 , DOI: 10.1021/acs.jpcc.3c01782
David Nielsen ₁ , Qi Gao ₁ , Ton V. W. Janssens ₂ , Peter N. R. Vennestrøm ₂ , Susanne Mossin ₁

Affiliation

H ₂程序升温还原 (TPR) 和电子顺磁共振 (EPR) 光谱广泛用于量化脱水 Cu-CHA 沸石中的两个 Cu 物种，即 Z 2 Cu（与 6 个 Al 结合的_Cu） -环）和ZCuOH（与一个Al缔合的Cu）。由于量化并不简单，因此仅基于一种方法的研究之间会出现差异。_{使用 H 2} -TPR 和 EPR对具有相同母体沸石材料的五个具有不同铜含量的样品进行了研究，以详细说明铜位点的可能定量。Z ₂ Cu 位点的正确量化需要模拟 EPR 谱并分析 H _{2的高斯拟合}-每个物种科的 TPR 数据。_{为了使 EPR 和 H 2 -TPR 在 Z}₂ Cu 位点的定量上达成一致，将 TPR 中的两个高温还原峰（约 350 和 530 °C）加在一起。据推测，TPR 中的复合低温还原峰（约 215 和 250 °C）由不同类型的 ZCuOH 组成，其中一些是 EPR 沉默的，一些给出了宽广且模糊的 EPR 谱。我们的分析表明，最稳定位点 Z ₂ Cu 中的 Cu 含量接近于骨架中 Al 随机分布假设所预测的含量。_{然而，EPR 谱的超精细耦合模式表明，在 Z 2}范围内Cu 位点，在这种特定的 CHA 沸石中，两种可能类型之间存在不均匀分布。H ₂ -TPR 与原位 EPR 结合进一步揭示 Z ₂ Cu 位点之一比另一个更容易被还原。

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Cu-Speciation in Dehydrated CHA Zeolites Studied by H2-TPR and In Situ EPR

H₂-temperature-programmed reduction (TPR) and electronic paramagnetic resonance (EPR) spectroscopy are widely used to quantify two families of Cu-species in dehydrated Cu-CHA zeolites, namely, Z₂Cu (Cu associated with two Al in the 6-ring) and ZCuOH (Cu associated with one Al). Since quantification is not straightforward, discrepancies arise between investigations based on only one method. Five samples with the same parent zeolite material were investigated with different amounts of copper using both H₂-TPR and EPR to elaborate on the possible quantification of Cu-sites. Proper quantification of the Z₂Cu sites required simulation of the EPR spectra and analysis of the Gaussian fit of the H₂-TPR data for each family of species. To reach an agreement between EPR and H₂-TPR on the quantification of Z₂Cu sites, the two high-temperature reduction peaks in the TPR (ca. 350 and 530 °C) were added together. The composite low-temperature reduction peak in TPR (ca. 215 and 250 °C) is speculated to consist of different types of ZCuOH where some are EPR silent and some give a broad and indistinct EPR spectrum. Our analysis shows that the amount of Cu in the most stable sites, Z₂Cu, is close to the amount predicted by the assumption of a random distribution of Al in the framework. However, the hyperfine coupling pattern of the EPR spectra reveals that within the category of Z₂Cu sites, a non-even distribution exists between the two possible types in this particular CHA zeolite. H₂-TPR combined with in situ EPR further reveals that one of the Z₂Cu sites is more easily reduced than the other.

更新日期：2023-06-28

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