Thermally stable α-alumina supported ceria for coking resistance and oxidation of radical coke generated in-situ. (15th April 2018)

• Record Type: Journal Article
• Authors: Mahamulkar, Shilpa; Yin, Kehua; Claure, Micaela Taborga; Davis, Robert J.; Li, Liwei; Shibata, Hirokazu; Malek, Andrzej; Jones, Christopher W.; Agrawal, Pradeep K.
• Is Part Of: Fuel. Volume 218(2018)
• Page Start: 357
• Page End: 365
• Publication Date: 2018-04-15
• Subjects: Coking -- Coke – catalyst contact -- Tight contact -- Lattice oxygen -- Decoking; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2018.01.001
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: α-Alumina supported ceria catalysts show high activity towards coke oxidation. Ceria catalysts are observed to resist coking during pyrolysis. 50–80 mol% Ce catalysts showed optimal activity for coke oxidation. Coke oxidation on ceria – alumina catalysts driven by availability of surface oxygen. Abstract: A series of thermally stable α-alumina supported and unsupported ceria catalysts with varying composition is systematically investigated under realistic coke – catalyst contact conditions for the oxidation of in-situ generated coke during ethylene pyrolysis. These catalysts have been designed for use in high temperature applications of steam cracking. The textural and structural characterization of α-alumina supported ceria catalysts show the absence of solid oxide solutions, with the supported catalysts having distinct ceria domains on the alumina support. For comparison, two types of coke – catalyst contacting are explored: (i) tight contact by grinding industrial coke with catalyst and (ii) realistic in-situ contact, where coke is deposited on the catalytic support. During in-situ coke deposition, ceria-containing catalysts demonstrate resistance to coking as compared to the bare α-alumina support. Ceria and ceria – alumina composites also enabled coke oxidation at lower temperatures than the un-catalyzed coke oxidation. The presence of both Ce 3+ and Ce 4+ is confirmed by X-ray absorption near edge structure (XANES), consistent with the well-known redox capability of ceria catalysts. Kinetic studies revealed 50–80 mol% Ce as the best compositions for oxidation activity towards both industrial and in-situ coke. The catalytic activity correlates with the presence of reactive lattice oxygen atoms on ceria for both types of contact, indicating a similar mechanism of carbon oxidation under in-situ contact and tight contact conditions. A mechanism of reaction involving lattice oxygen of ceria is proposed for the oxidation of coke as well as for retardation of coke deposition on ceria domains.