Influence of electronic state and dispersion of platinum particles on the conversion and selectivity of hydrogenation of an α,β-unsaturated aldehyde in supercritical carbon dioxide

The selective hydrogenation of cinnamaldehyde (CAL) was investigated using silica supported platinum catalysts in supercritical carbon dioxide. Selectivity to cinnamyl alcohol (COL) is enhanced as Pt⁰/Pt²⁺ ratio increases; namely, zero-valent metallic surface is beneficial to the formation of COL compared with less reduced surface. The influence of Pt⁰/Pt²⁺ ratio is more significant on the selectivity than on the total conversion. For the catalyst with small Pt⁰/Pt²⁺ value, the selectivity also depends on the degree of platinum dispersion. The selectivity to COL is higher for higher degree of platinum dispersion. The CO₂ pressure did not affect the conversion and selectivity so much.