Ag–Pd/TiO2 catalysts prepared by the strong electrostatic adsorption and electroless deposition with θAg 0–0.92.

TiO 2 supported Pd-Au catalysts were prepared with Pd (0.5 wt-%) by impregnation and then Au (1.0 wt-%) by deposition-precipitation (Au/Pd/TiO 2) and vice versa (Pd/Au/TiO 2). For the former sample, the state of dispersion of Pd on TiO 2 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 alloy formation was not clearly detected on the Pd/Au/TiO 2 and the electronic properties of Pd were not so different from those of monometallic Pd/TiO 2. All the catalysts were selective to 1heptene (> 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 min for the Au/Pd/TiO 2 while it still remained > 60% for the Pd/Au/TiO 2 similar to the monometallic Pd/TiO 2 catalyst. The rate of 1-heptene hydrogenation (in the second step) did not depend on the Pd dispersion but was found to be greatly enhanced as the Pd species became electron-rich in the Au-Pd alloy particles. The modification of Pd species by Au was less significant for the first step of hydrogenation of 1-heptyne to 1-heptene.

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