Thermally stable α-alumina supported ceria for coking resistance and oxidation of radical coke generated in-situ

FUEL

卷:218

Article

Mahamulkar, Shilpa¹  Yin, Kehua²  Claure, Micaela Taborga¹  Davis, Robert J.²  Li, Liwei⁵  Shibata, Hirokazu^3,6  Malek, Andrzej⁴  Jones, Christopher W.¹  Agrawal, Pradeep K.¹ 

[1] Georgia Inst Technol, Sch Chem & Biomol Engn, Atlanta, GA 30332 USA

[2] Univ Virginia, Dept Chem Engn, Charlottesville, VA 22904 USA

[3] Dow Chem Japan, Dow Olymp & Sports Solut, Shinagawa Ku, 2-2-24 Higashi Shinagawa, Tokyo 1408617, Japan

[4] Dow Chem Co USA, Hydrocarbons R&D, Midland, MI 48674 USA

[5] Dow Chem Co USA, Hydrocarbons R&D, Freeport, TX 77541 USA

[6] Dow Benelux, Hydrocarbons R&D, Hoek, Netherlands

关键词: Coking;    Coke - catalyst contact;    Tight contact;    Lattice oxygen;    Decoking;   

DOI  :  10.1016/j.fuel.2018.01.001

来源: Elsevier

【 摘 要 】

A series of thermally stable alpha-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 alpha-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 alpha-alumina support. Ceria and ceria - alumina composites also enabled coke oxidation at lower temperatures than the un-catalyzed coke oxidation. The presence of both Ce3+ and Ce4+ 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.

【 授权许可】

Free