The effect of precursors salts on surface state of Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts

Abstract

The influence of the precursors on the promoting effect of ceria on Pd/Al 2 O 3 catalyst, when ceria is coated over alumina was studied. The reaction of propane oxidation proceeded under different feed conditions and the surface active sites were characterized by X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance spectroscopy (DRS).XPS and DRS results show that PdO/Pd 0 interface are the active sites independent of the precursor, while the catalysts containing CeO 2 showed formation of palladium species in the highest oxidation state, probably PdO 2 (338 eV) after the oxidation of propane. Besides, the O/Al and O/Ce ratios evidenced the increase of oxygen storage in the presence of CeO 2 . In addition, the precursor acetylacetonate favors the oxygen storage in the lattice.

Interpretation of kinetic data with selected characterizations of active sites

“…On the other hand, with water the effect of the partial pressure of oxygen exhibited negative values of b = À0.7. We observed re-dispersion of Pd after introducing water in the reactants, which means that these reactants are strongly adsorbed provoking a negative order for g = À0.6 [48].…”