Tungsten and molybdenum were introduced in gamma-Al2O3 and Pd/gamma-Al2O3 using metalcarbonyls [W(CO)(6) and MO(CO)(6)] photoactivation. DRIFTS FT-IR spectra of the surfaces prior to thermal decomposition reveal the presence of unstable metalsubcarbonyl species, in contrast with the ones found previously, when the photoactivation was performed in the presence of triphenylphosphine. The nu(CO) band intensities did not reflect the tungsten and molybdenum uptakes determined by AAS, the loadings being higher, in the presence of palladium. After thermal treatment, the catalysts were further characterized by hydrogen chemisorption and FT-IR spectra of adsorbed CO and NO. The results showed that a reaction between the hexacarbonyls and the supported palladium particles takes place leading to bimetallic catalysts, with clear palladium-tungsten and palladium-molybdenum interactions. Pd + Mo(CO)(6) double right arrow Pd-uv + Mo(CO)(6-x) double right arrow Pd-Mo(CO)(6-x) double right arrow Pd-uv-MO. Both group VI metals strongly modify the chemisorption properties of palladium, while molybdenum seems to be present in a reduced state in close association with palladium. (C) 2002 Elsevier Science B.V. All rights reserved.