The liquid-phase hydrogenation of 1-heptyne over Pd-Au/TiO2 catalysts prepared by the combination of incipient wetness impregnation and deposition-precipitation

TiO2-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) and vice versa (Pd/Au/TiO2). 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 alloy formation was not clearly detected on the Pd/Au/TiO2, and the electronic properties of Pd were not so different from those of monometallic Pd/TiO2. All the catalysts were selective to 1-heptene (> 95%) until close to the complete conversion of 1-heptyne. However, the selectivity of 1-heptene drastically decreased to 0% (which was further hydrogenated to heptane) in 120 min for the Au/Pd/TiO2 while it still remained > 60% for the Pd/Au/TiO2 similar to the monometallic Pd/TiO2 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. (c) 2012 Elsevier Inc. All rights reserved.