Deactivation characteristics of Ni/CeO2-Al2O3 catalyst for cyclic regeneration in a portable steam reformer
The requirements of process parameters, e.g. air pump flow rate and operational pressure are restricted by confined space and limit the performance of portable steam propane reformer. This makes it difficult to operate a catalyst in the portable reformer under mild operation conditions. Hence, the catalyst can be rapidly deactivated. The deactivation behavior of Ni/CeO2-Al2O3 catalyst was investigated for coke deposition and active metal sintering. Coke formation by the propane pyrolysis was predominantly responsible for deactivation at low reaction temperature. Coke formation can be thermodynamically reduced by elevating the temperature and hence the steam reformer was operated at high temperature to inhibit coke formation. Although the Ni/CeO2-Al2O3 catalyst made small amounts of coke at high temperature, it was deactivated by the encapsulated carbon on active metal during long term operation. Because a compact air pump for catalyst regeneration was available during the shut-down procedure of our portable fuel cell system, the catalysts could be regenerated by coke oxidation. The cyclic oxidation was useful for long term operation. The properties of the used catalyst and the coke were investigated by XRD, NEXAFS, XANES-TPO, TGA and TEM. The Ni/CeO2-Al2O3 catalyst in our portable reformer showed stable activity for steam propane reforming in cyclic oxidation operation for 500 h.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The active sites favored the formation of the carbidic carbon at high temperature. ► An interaction between the CeO2 and Al2O3 was observed at high temperature. ► The nickel species were oxidized and reduced during the cyclic oxidation procedure. ► The deactivation under the cyclic oxidation condition is low in the long run test.
Journal: Applied Catalysis B: Environmental - Volumes 111–112, 12 January 2012, Pages 157–164