Methane oxidation on alumina supported palladium catalysts: Effect of Pd precursor and solvent

Palladium precursors and solvents were studied for their effects on the activities of alumina-based palladium catalysts in methane combustion and the resistance of the catalysts to thermal aging. The properties of the catalysts were compared with those of a commercial reference. The palladium precursors were Pd(propionate)(2), Pd(acetate)(2) and Pd(acetyl acetonate)(2) and the solvents were acetone, acetic acid, propionic acid and toluene. Catalysts were prepared by the wet impregnation method. Catalysts were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). The surface areas were measured by Brunauer-Emmett-Teller method (BET). Acidity of the alumina support was measured by NH3 desorption. Activities of the catalysts in methane oxidation were screened under lean burn conditions. In methane oxidation with fresh catalyst, the best performance was obtained with a combination of Pd(acetate)(2) and acetic or propionic acid. The light-off temperatures of the fresh catalysts (562 K and respectively) were slightly lower than the light-off temperature (567 K) of the commercial 557 K, reference. Differences between the light-off temperatures of the aged and fresh catalysts were least when the catalysts were prepared with Pd(acetyl acetonate)(2) as Pd precursor and in acetic or propionic acid as solvent: +12 K and +18 K, respectively. The corresponding value for the reference was +64 K. For several of the fresh catalysts, conversion in methane oxidation at 623 K was over 90%. A comparison of methane combustion and NH3 desorption results indicated that acidity of the support material affects catalysts activity. (C) 2009 Elsevier B.V. All rights reserved.