The performance and stability of supported Pd catalysts were investigated in the partial oxidation of geraniol with molecular oxygen in dense CO2. All catalysts deactivated to a certain extent in the continuous-flow reactor; the least stable among them was Pd/Al2O3. Beside oxidative dehydrogenation, isomerization and hydrogenation reactions were also catalyzed by Pd. The initial selectivity of Pd to citral formation was only 50-60% but improved up to 90% with time-on-stream. The extensive catalyst deactivation and the shift in product distribution are (partly) attributed to formation of geranic (neric) acid, and the acid-catalyzed dimerization and oligomerization of reactant and products leading to site blocking by the high molecular weight. by-products. ATR-IR spectroscopy revealed that no CO was present on the Pd surface during geraniol oxidation though it appeared in the absence of oxygen. A shift from two-phase to single phase conditions diminished the reaction rate, presumably due to accumulation of water co-product on the catalyst surface. Despite of the initial deactivation of Pd/SiO2, an outstanding TOF of 169 h(-1) was achieved on the stabilized catalyst under steady state conditions, at 80 degrees C and 150 bar. (c) 2005 Elsevier B.V. All rights reserved.