Magnesia-supported palladium catalysts were prepared from chemical vapour deposition (CVD) of [Pd(C3H5)(C5H5)] and incipient wetness impregnation of [Pd(C3H5)Cl](2) and [Pd(acac)(2)]. DRIFT spectroscopy of adsorbed CO on prereduced catalysts indicates that the electronic state of metal particles depends on the preparation methodology and markedly on the organometallic precursor. Inn-heptane reforming at 500 degrees C, the highest activity and selectivity were shown by the CVD-based system. Chloride ions deriving from the impregnation solvent exchange with surface hydroxyls. Acidic Mg-Cl sites are thus formed, which induce a beneficial effect on the catalytic properties. The reforming activity collapsed when a chlorine-containing precursor was used, due to a partial coverage of the palladium surface with chemisorbed chlorine atoms.