The effect of the calcination  temperature (up to 900°C) on the catalytic activity of Pd-CeO₂/Al₂O₃ catalysts of  large Pd particle mean size (≥ 5nm) was studied. Activity in methylcyclopentane (MCP) hydrogenolysis, 2-methylpentane (2MP) isomerization and 3-methylpentane (3MH) aromatization reaches a high level between 200 and 450°C, but decreases sharply beyond this calcination temperature range. Using 13C labelled 2MP and 3MP reagents, we pointed out an increase in the isomerization selectivity. This isomerization according to the cyclic mechanism is competitive with hydrocracking. X-Ray photoemission spectroscopy (XPS) was performed first on the used catalysts followed by an in-situ H₂ reduction. These results, combined with XRD, elemental analyses, BET measurements, TEM investigations and X-Ray absorption (XAS) on the Ce L_III edge,yield information on the nature of the Pd and CeO_x species formed on the surface of these catalysts and their interaction. Palladium exhibits at least two forms, the metallic one and a partially chlorided form which is released by in situ reduction. A new method to determine the cerium oxidation state from a shapeline analysis of the 3d core level is developed. In this fitting process the inelastic contribution (background) is simulated by using a formulation due to Tougaard and Sigmund (1982). We then determine the Ce III content with a better accuracy. The limitations of the method are discussed. A mixture of Ce III and IV oxidation states is then obtained on all of the samples. Large variations of their respective amounts are observed according to the calcination temperature and the reduction treatment. The occurrence of a Ce III oxidation state is assigned to hydroxide (low calcination temperature) and oxychloride (low and medium calcination temperature) formation. At high calcination temperature most of the chlorine evolves and ceria forms. A Pd species at high binding energy (338.0-338.5 eV) is evidenced on the as used catalysts, whose optimum lays in the 200-450°C calcination range. This species is assigned to a partially chlorided palladium. Even after the in situ reduction the difference of binding energies Pd 3d5/2 - Cl 2p remains much larger than on the unpromoted catalyst. This is interpreted as a still persisting interaction. Owing to this strong interaction, we postulate that new catalytic sites are created at the interface of the transition metal particle and the rare earth oxychloride phase. Interaction occurs through chloride ions which confer an electron-deficient character to palladium. Thus palladium  exhibits on these sites a high intrinsic activity and selectivity modifications through selective formation of σ Pd-C bonds and less  dehydrogenated intermediates. A fair correlation is found between the catalytic activity and the chlorided palladium content. The increase in 3MH aromatization selectivity in the calcination range (200-450°C) is explained by the occurrence of a bifunctionnal mechanism, the acidic sites of the support being provided by the chloride ions.