How do Core–Shell Structure Features Impact on the Activity/Stability of the Co‐based Catalyst in Dry Reforming of Methane?

• Published in: ChemCatChem Vol. 10; no. 13; pp. 2845 - 2857
• Main Authors: Pang, Yijun, Zhong, Aihua, Xu, Zhijia, Jiang, Wu, Gu, Lingli, Feng, Xinzhen, Ji, Weijie, Au, Chak‐Tong
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 09.07.2018
• Subjects: Catalysis; Catalysts; Catalytic activity; cobalt; Coking; Core-shell structure; Deactivation; Methane; nanocatalyst; nanomaterials; Oxidation; Particle size; Reforming; Shell stability; Shells; Silicon dioxide; X ray photoelectron spectroscopy
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201800327

Dry reforming of methane has been systematically investigated over a series of x‐Co@SiO2‐y catalysts where x is the Co particle size ranging from 11.1 to 121.3 nm while y denotes the silica shell thickness ranging from 6.0 to 21.9 nm. Various techniques including TEM, XRD, H2‐TPR/‐TPD, XPS, BET, O2‐TPO, TG, and H2‐TPSR‐MS were employed to characterize physicochemical properties of catalysts. H2‐TPR and XPS results indicate that the core–shell interaction is dependent on the core size: the smaller the Co particle size is; the stronger the core–shell interaction. The investigations employing H2‐TRSR‐MS and XPS on the spent catalysts demonstrated that a fraction of metallic Co was re‐oxidized on a large‐core catalyst such as 121.3‐Co@SiO2‐72.2 during the reaction, and such oxidation leads to lower catalytic activity and stability. O2‐TPO results indicated that the catalyst with smaller core size caused significant coking. TG analysis together with TEM investigation on the used samples suggested that carbon deposition is notably core‐size‐dependent and responsible for deactivation of the small‐core catalyst. Among various core–shell structured catalysts, 27.8‐Co@SiO2‐14.3 showed superior activity and durability, owing to the well‐balanced property between coking and anti‐oxidation of Co cores. Size matters: A catalyst with a small Co core and thin SiO2 shell resulted in heavy carbon deposits while a catalyst with large Co core and thick SiO2 shell caused oxidation of the Co core during the dry reforming of methane (DRM). A well‐balanced carbon deposition and core oxidation is achievable by fine tuning core size and shell thickness, giving superior catalytic activity and stability.