Insight into the Microstructure and Deactivation Effects on Commercial NiMo/γ-Al2O3 Catalyst through Aberration-Corrected Scanning Transmission Electron Microscopy

Autor: Le Zhang, Wei Han, Guangtong Xu, Limei Qiu, Wenhui He, Wei Wang, Yanjuan Xiang, Aiguo Zheng, Anpeng Hu
Rok vydání: 2019
Předmět:
Zdroj: Catalysts
Volume 9
Issue 10
Catalysts, Vol 9, Iss 10, p 810 (2019)
ISSN: 2073-4344
Popis: Atom-resolved microstructure variations and deactivation effects on the commercial NiMo/&gamma
Al2O3 catalysts were revealed by aberration-corrected scanning transmission electron microscope (Cs-STEM) equipped with enhanced energy dispersive X-ray spectroscopy (EDS). Structural information parallel to and vertical to the electron beam provides definitive insight toward an understanding of structure&ndash
activity relations. Under the mild to harsher reaction conditions, &ldquo
fragment&rdquo
structures (like metal single atoms, metal clusters, and nanoparticles) of commercial NiMo/&gamma
Al2O3 catalysts, gradually reduces, while MoS2 nanoslabs get longer and thinner. Such a result about active slabs leads to the reduction in the number of active sites, resulting in a significant decrease in activity. Likewise, the average atomic ratio of promoter Ni and Ni/(Mo + S) ratio of slabs decrease from 2.53% to 0.45% and from 0.0788 to 0.0326, respectively, by means of EDS under the same conditions stated above, reflecting the weakening of the promotional effect. XPS result confirms the existence of NixSy species in deactivated catalysts. This could be ascribed to the Ni segregation from active phase. Furthermore, statistical data give realistic coke behaviors associated with the active metals. With catalytic activity decreasing, the coke on the active metals regions tends to increase faster than that on the support regions. This highlights that the commercial NiMo/&gamma
Al2O3 catalyst during catalysis is prone to produce more coke on the active metal areas.
Databáze: OpenAIRE
Nepřihlášeným uživatelům se plný text nezobrazuje