Segregation of Pt and Re During CO 2 Reforming of CH 4
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Catalysis Letters Vol. 103, Nos. 1–2, September 2005 (Ó 2005) DOI: 10.1007/s10562-005-6505-7
Segregation of Pt and Re during CO2 reforming of CH4 Sean G. Mueller, Patrick J. Stallbaumer, David A. Slade, and Susan M. Stagg-Williams* Chemical and Petroleum Engineering Department, University of Kansas, 1530 W. 15th Street, 4132 Learned Hall, Lawrence, KS, 66045 USA
Received 28 January 2005; accepted 6 May 2005
Pt–Re supported on Ce0.52 Zr0.48 O2 was studied for the carbon dioxide reforming of methane at 800 °C. Diffuse reflectance fourier transform infrared spectroscopy and temperature programmed reduction studies suggest that Pt and Re segregation occurs during the reaction. The segregation results in an increase in the Pt sites available for CH4 decomposition and results in the bimetallic catalyst exhibiting an increase in the conversion of methane with time on stream. After 20 h of reaction, the CH4 conversion observed for the bimetallic catalyst was the same as the CH4 conversion observed for the monometallic catalyst. KEY WORDS: CH4 reforming; Pt–Re; bimetallic; syngas production; segregation.
1. Introduction Steam reforming of methane has been traditionally used to produce synthesis gas with high H2:CO product ratios [1,2]. However, research over the past years has shown the carbon dioxide (dry) reforming of methane to be a promising alternative. The primary benefit of dry reforming is derived from its low H2:CO ratio, which is preferred for hydroformylation, carbonylation, FischerTropsch synthesis [3], and production of oxygenated compounds. Also, the combination of dry reforming with steam reforming and partial oxidation allows for a tunable reaction to achieve a target syngas ratio [4,5]. Commercialization of dry reforming has been limited due to equilibrium considerations and its highly endothermic nature, which require temperatures near 800 °C for acceptable conversions [6,7]. At such temperatures, the catalyst deactivates due to carbon deposition. Supports with low acidity and high oxygen mobility have been studied as a means of reducing carbon deposition [8–11]. For example, the promotion of ZrO2 with Ce has been shown to increase the stability of the catalyst [8] for the dry reforming reaction. The enhanced performance has been ascribed to several factors including the ability of the promoters to retard Pt particle growth and the increased oxygen storage and release capability of the support. Both of these promotional effects increase the long term activity. The higher dispersion increases the metal sites available for CH4 decomposition and the promoters provide oxygen to the metal-support interface which facilitates the removal of carbon from the surface of the metal particle [8]. In the naphtha reforming literature, promoters such as Re have been used to prevent carbon deposition [12]. * To whom correspondence should be addressed. E-mail: [email protected]
Increasing the Pt–Re interaction has been shown to reduce coke deposition [13], improve Pt dispersion [14], increase surface area, and significantly
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