Palladium-catalysed dehydrogenation of 1-phenylethanol in dense carbon dioxide

Abstract

Abstract The feasibility of the heterogeneous catalytic dehydrogenation of alcohols in dense (sub- and supercritical) carbon dioxide is shown by the transformation of 1-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 155 °C) 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 °C, 30–190 bar, CO2/alcohol molar ratio: 30–360). Reaction rate and ketone selectivity were favored at high temperature (around 150 °C), 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.