Deactivation characteristics of lanthanide-promoted sol-gel Ni/Al2O3 catalysts in propane steam reforming

被引:282
作者
Natesakhawat, S [1 ]
Watson, RB [1 ]
Wang, XQ [1 ]
Ozkan, US [1 ]
机构
[1] Ohio State Univ, Dept Chem & Biomol Engn, Columbus, OH 43210 USA
基金
美国国家科学基金会;
关键词
nickel; lanthanides; ceria; sol-gel; steam reforming; hydrogen; deactivation; sintering; coke formation; gasification;
D O I
10.1016/j.jcat.2005.07.014
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Lanthanide-promoted sol-gel nickel catalysts supported on alumina were studied with regard to their activity and stability for propane steam reforming. X-Ray photoelectron spectroscopy, in situ X-ray diffraction, temperature-programmed oxidation, transmission electron microscopy, thermogravimetric analysis coupled with temperature-programmed reaction, and sequential temperature-programmed coking/gasification/hydrogenation were used to investigate the deactivation characteristics of the catalysts prepared. Adding small amounts (2 wt%) of lanthanide elements (i.e., La, Ce, and Yb) significantly improves steam reforming activity and stability. Although the catalysts deactivate more rapidly at higher reaction temperature, the activity loss can be suppressed by increasing the H(2)O/C ratio. The catalyst deactivation can be attributed to a combination of nickel sintering and coke formation. In addition, there appears to be partial oxidation of metallic sites after exposure to the reaction medium. Lanthanides cause enhanced sintering resistance, leading to smaller nickel crystallites in Ni/Al(2)O(3) catalysts. Cerium promotion effectively inhibits coking by increasing active oxygen species on the nickel surface due to enhanced water adsorption and gasification. Incorporation of cerium also reduces the dissolution and diffusion of carbon through nickel particles, thus preventing the formation of carbon filaments. (c) 2005 Elsevier Inc. All rights reserved.
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页码:496 / 508
页数:13
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