CO Oxidation on Pd/Al2O3 Catalysts under Stoichiometric Conditions

Abstract

This paper deals with the CO oxidation on Pd/Al2O3 catalysts under stoichiometric conditions relevant for the after-treatment of gasoline exhaust. A series of catalysts was prepared by incipient wetness impregnation, whereas the Pd load was systematically varied from 0.1 to 5 wt%. The samples were physical-chemically characterized by using N2 physisorption (BET, BJH), powder X-ray diffraction (PXRD), temperature programmed desorption of H2 (HTPD), temperature programmed desorption of CO (CO-TPD) and transmission electron microscopy (TEM). The performance of the powder catalysts was evaluated on a laboratory test bench employing a simple gasoline model exhaust with stoichiometric CO and O2 fractions. From the characterization data it was deduced that the Pd dispersion of the catalysts decreases with precious metal load corresponding to increase in mean Pd particle size going up from ca. 5–12 nm. The correlation of the physical–chemical characteristics with the CO oxidation activity of the Pd/Al2O3 samples clearly indicated that the catalytic efficiency was predominately driven by the number of active Pd sites, whereas no size effect of the Pd entities was found.