Molecular Biophysics Group, Department of Physics, Utrecht University, Princetonplein 1, 3508 TA Utrecht, The Netherlands.
Chemistry. 2013 Mar 18;19(12):3846-59. doi: 10.1002/chem.201203491. Epub 2013 Feb 27.
While cycling through a fluid catalytic cracking (FCC) unit, the structure and performance of FCC catalyst particles are severely affected. In this study, we set out to characterize the damage to commercial equilibrium catalyst particles, further denoted as ECat samples, and map the different pathways involved in their deactivation in a practical unit. The degradation was studied on a structural and a functional level. Transmission electron microscopy (TEM) of ECat samples revealed several structural features; including zeolite crystals that were partly or fully severed, mesoporous, macroporous, and/or amorphous. These defects were then correlated to structural features observed in FCC particles that were treated with different levels of hydrothermal deactivation. This allowed us not only to identify which features observed in ECat samples were a result of hydrothermal deactivation, but also to determine the severity of treatments resulting in these defects. For functional characterization of the ECat sample, the Brønsted acidity within individual FCC particles was studied by a selective fluorescent probe reaction with 4-fluorostyrene. Integrated laser and electron microscopy (iLEM) allowed correlating this Brønsted acidity to structural features by combining a fluorescence and a transmission electron microscope in a single set-up. Together, these analyses allowed us to postulate a plausible model for the degradation of zeolite crystals in FCC particles in the ECat sample. Furthermore, the distribution of the various deactivation processes within particles of different ages was studied. A rim of completely deactivated zeolites surrounding each particle in the ECat sample was identified by using iLEM. These zeolites, which were never observed in fresh or steam-deactivated samples, contained clots of dense structures. The structures are proposed to be carbonaceous deposits formed during the cracking process, and seem resistant towards burning off during catalyst regeneration.
在流化催化裂化 (FCC) 单元中循环时，FCC 催化剂颗粒的结构和性能会受到严重影响。在这项研究中，我们着手研究商业平衡催化剂颗粒（进一步表示为 ECat 样品）的损坏，并绘制其在实际单元中失活所涉及的不同途径。降解在结构和功能水平上进行了研究。ECat 样品的透射电子显微镜 (TEM) 揭示了几种结构特征；包括部分或完全断裂的沸石晶体、中孔、大孔和/或无定形。然后，将这些缺陷与在不同水平的水热失活下处理的 FCC 颗粒中观察到的结构特征相关联。这不仅使我们能够识别出在 ECat 样品中观察到的哪些特征是水热失活的结果，还能够确定导致这些缺陷的处理的严重程度。为了对 ECat 样品进行功能表征，通过与 4-氟苯乙烯的选择性荧光探针反应研究了单个 FCC 颗粒中的 Brønsted 酸度。集成激光和电子显微镜 (iLEM) 通过在单个装置中组合荧光和透射电子显微镜，允许将这种 Brønsted 酸度与结构特征相关联。这些分析共同使我们能够提出一个合理的模型，用于解释 ECat 样品中 FCC 颗粒中沸石晶体的降解。此外，还研究了不同年龄的颗粒内各种失活过程的分布。通过使用 iLEM，在 ECat 样品中的每个颗粒周围识别出完全失活的沸石的边缘。这些沸石从未在新鲜或蒸汽失活的样品中观察到，其中包含密集结构的凝块。这些结构被提议为在裂化过程中形成的碳质沉积物，并且在催化剂再生过程中似乎不易燃烧掉。
