Low-temperature conversion of phenol into CO, CO 2 and H 2 by steam reforming over La-containing supported Rh catalysts
AuthorConstantinou, D. A.
álvarez-Galván, M. C.
Fierro, José Luis García
Efstathiou, Angelos M.
SourceApplied Catalysis B: Environmental
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The steam reforming of phenol in the low-temperature range of 350-550°C was studied over 0.5wt% Rh supported on Ce 0.15Zr 0.85O 2, Zr 0.93La 0.07O 2, and Ce 0.13Zr 0.83La 0.04O 2 mixed metal oxides. The reforming specific activity (per gram of catalyst basis) was found to depend on (a) Rh dispersion, (b) the concentration (μmolg -1) of labile oxygen species of support, as determined by " oxygen storage capacity" measurements, and (c) the promotion of the water-gas shift (WGS) reaction rate, all of which largely influenced by the support chemical composition. The addition of 4atom% La 3+ into the Ce 0.15Zr 0.85O 2 crystal structure was found to largely promote the dispersion of Rh, to increase significantly (by a factor of 1.75) the concentration of surface basic sites (μmolm -2) of Ce 0.13Zr 0.83La 0.04O 2 compared to Ce 0.15Zr 0.85O 2 support, to prevent to a large extent the inhibiting role of hydrogen in the rate of WGS reaction, and to influence significantly the concentration and structure of surface reaction intermediates of the WGS, namely: formate (HCOO-) and -OH groups formed on the support, and adsorbed CO formed on the Rh metal. The 0.5wt% Rh/Ce 0.13Zr 0.83La 0.04O 2 catalyst led to a significantly better performance towards steam reforming of phenol in terms of phenol conversion, H 2-yield, and CO/CO 2 product ratio in the 350-450°C range compared to a commercial Ni-based catalyst (44wt% Ni) used for steam reforming reactions. At 400°C, the 0.5wt% Rh/Ce 0.13Zr 0.83La 0.04O 2 catalyst exhibited approximately 54% and 50%, respectively, higher phenol conversion and hydrogen yield, compared to the Ni-based industrial catalyst. The significantly lower CO/CO 2 product ratio obtained in the case of Rh/Ce 0.13Zr 0.83La 0.04O 2 compared to that obtained in the other supported-Rh catalysts is in agreement with the higher kinetic rate for the WGS reaction observed in the former catalyst. © 2012 Elsevier B.V.
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