Showing papers by "Luca Lietti published in 2006"

Methane combustion over PdO-alumina catalysts: the effect of palladium precursors

Abstract: The role of palladium precursors and the preparation route in the catalytic properties of PdO/Al2O3 catalysts toward methane oxidation was investigated in this paper. The catalysts were prepared using palladium chloride, nitrate and acetylacetonate as precursors and the preparation routes employed were impregnation of alumina with solutions of these precursors and the polyol method, in which palladium deposition is carried in a liquid polyol, e.g. ethylene glycol. All catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), surface area measurements and temperature programmed desorption of O2 (TPD). Unsteady-state methane oxidation was carried out by temperature-programmed surface reaction (TPSR). The results obtained suggested that the use of different palladium precursors and preparation routes played an important role on the properties of the catalysts, as palladium particle size, thermal stability of PdO and catalytic properties toward methane combustion. The use of palladium acetylacetonate as precursor by the impregnation method generated well-dispersed PdO particles on alumina. Regarding the PdO thermal stability and the activity toward methane combustion, this catalyst also presented the highest thermal stability and catalytic activity.

Simultaneous removal of NOx and soot on Pt–Ba/Al2O3 NSR catalysts

Abstract: The potentiality of a typical Pt–Ba/Al2O3 NSR catalyst in the simultaneous removal of particulate matter (soot) and NOx is investigated in this work, and compared with that of a Pt/Al2O3 sample. The behaviour of the catalyst in the soot combustion and NOx removal has been separately analyzed by means of temperature programmed oxidation (TPO) experiments, isothermal combustions and transient response method (TRM), respectively. The results show that in presence of only oxygen, soot oxidation occurs slowly even at a temperature as high as 400 °C. On the other hand, the presence of NO greatly increases the rate of soot conversion, which becomes significant at 350 °C. The capability of the Pt–Ba/Al2O3 and Pt/Al2O3 catalysts to accomplish the removal of NOx in the absence and in the presence of soot was investigated under cycling conditions, i.e. alternating lean-rich phases according to the typical NSR strategy. It has been found that the Pt–Ba/Al2O3 sample is able to simultaneously remove both soot and NOx, as opposite to the Pt/Al2O3 catalyst which effectively performs the soot oxidation but is not able to remove gas phase NOx to a significant extent. The presence of soot does not significantly affect the activity in the NOx reduction of the Pt–Ba/Al2O3 catalyst. The comparable level of activity in the soot combustion which is observed between the Pt/Al2O3 and the Pt–Ba/Al2O3 sample in spite of the fact that the ternary sample accomplishes the removal of NOx in the gas phase has been tentatively ascribed to specific oxidizing properties of the stored nitrate species.