Selective hydrogenation of citral over Au-based bimetallic catalysts in supercritical carbon dioxide

Selective hydrogenation of citral was investigated over Au-based bimetallic catalysts in the environmentally benign supercritical carbon dioxide (scCO₂) medium. The catalytic performances were different in citral hydrogenation when Pd or Ru was mixed (physically and chemically) with Au. Compared with the corresponding monometallic catalyst, the total conversion and the selectivity to citronellal (CAL) were significantly enhanced over TiO₂ supported Pd and Au bimetallic catalysts (physically and chemically mixed); however, the conversion and selectivity did not change when Ru was physically mixed with Au catalyst compared to the monometallic Ru/TiO₂, and the chemically mixed Ru-Au/TiO₂ catalyst did not show any activity. The effect of CO₂ pressure on the conversion of citral and product selectivity was significantly different over the Au/TiO₂, Pd-Au/TiO₂, and Pd/TiO₂ catalysts. It was assumed to be ascribed to the difference in the interactions between Au, Pd nanoparticles and CO₂ under different CO₂ pressures.