LIQUID-PHASE SELECTIVE HYDROGENATION OF 1-HEPTYNE OVER Au-Pd/TiO2 CATALYSTS

Abstract

TiO2_100 supported Pd-Au catalysts were prepared with Pd (0.5 wt%) by impregnation and then Au (1.0 wt%) by deposition-precipitation (Au/Pd/TiO2_100) and vice versa (Pd/Au/TiO2_100). For the former sample, the state of dispersion of Pd on TiO2 changed during the loading of Au, resulting in the formation of small Au-Pd alloy particles and thus changing the electronic properties of Pd species. The electronic properties of Pd on Pd/Au/TiO2_100 were not so different from those of monometallic Pd/TiO2_100. Moreover the nanocrystalline TiO2 materials (9 and 15 nm) were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO2 catalysts. The Pd metal and/or Pd-Au alloy formed on the TiO2_9 (< 1 nm) were smaller than on TiO2_15 (2-3 nm) and on TiO2_100 (4-10 nm). All the catalysts were selective to 1-heptene (> 95%) until close to the complete conversion of 1-hetyne. However, the selectivity of 1-heptene drastically decreased to 0% (which was further hydrogenated to heptane) in 120 minute for the Au/Pd/TiO2_100 while it still remained > 40% for the Au/Pd/TiO2_9, Au/Pd/TiO2_15 and the monometallic Pd/TiO2 catalyst.