Influence of Phase Behavior on the Selective Hydrogenation of Cinnamaldehyde with Ruthenium Complexes in Supercritical Carbon Dioxide

Abstract

The phase behavior has significant effects on the activity and selectivity of Ru complexes for cinnamaldehdye (CAL) hydrogenation in supercritical carbon dioxide (scCO₂). A single phase formed in scCO₂ is more effective for selective hydrogenation of C=C bond, while the presence of two phases (CO₂ gas and CAL liquid phases) benefits the hydrogenation of C=O bond. In this two-phase hydrogenation, the reaction rate increases with increasing CO₂ pressure and the selectivity to cinnamyl alcohol (COL) depends on both CO₂ pressure and CAL concentration. Visual observations show that the CAL liquid phase expands at high CO₂ pressures due to dissolution of CO₂ and H₂, and this contributes to the enhancement of the reaction rate and the COL selectivity.