The feasibility of the heterogeneous catalytic dehydrogenation of alcohols in dense (sub- and supercritical) carbon dioxide is shown by the transformation of I-phenylethanol in a continuous flow fixed-bed reactor. A 0.5 wt.% Pd/Al2O3 catalyst afforded reasonably good activity (turnover frequency (TOF): 15 h(-1) at 155degreesC and up to 100% selectivity to acetophenone. An interesting feature of the reaction is that the conversion and selectivity varied parallel under conditions investigated (80-165 degreesC, 30-190 bar, CO2/alcohol molar ratio: 30-360). Reaction rate and ketone selectivity were favored at high temperature (around 150degreesC), low total pressure (favourably in the subcritical region), high CO2 and low alcohol flow rates. Under these conditions, interfacial mass transport and removal of the co-product hydrogen is enhanced. No catalyst deactivation was observed within about 300 h on stream. (C) 2004 Elsevier B.V. All rights reserved.