As a prelude to the optimization of a continuous decontamination system, catalytic hydrogenations of selected tri-, tetra- and penta-cyclic aromatic hydrocarbon compounds over commercial alumina supported palladium were investigated under mild conditions (∼90°C/0.42MPa H 2 ) and interpreted in the light of reports from the literature. Acenaphthylene, acenaphthene, anthracene, phenanthrene, chrysene and benzo[α]pyrene were hydrogenated, virtually completely, to saturated polycyclic hydrocarbon compounds with no appreciable evidence of carbon–carbon bond rearrangement during equilibration. With comparable operating conditions, triphenylene was only partially hydrogenated; the central ring remained unsaturated. The effects of reaction temperature, time of equilibration and supporting gases on hydrogenation were evaluated. Whereas near-critical CO 2 had no perceptible influence on rate/course of the reaction, nitrogen decreased the reaction rate somewhat.