The effect of TiO2 particle size on the characteristics of Au–Pd/TiO2 catalysts

• Au–Pd catalysts were prepared on TiO2 with average crystallite sizes 9 and 15 nm.
• The size of Au–Pd alloy depended on the TiO2 crystallite size.
• Electronic effect by Au–Pd alloy formation was more pronounced on the larger TiO2.
• Au acted as an electronic promoter for Pd, which promoted 1-heptene hydrogenation.

The nanocrystalline TiO2 materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO2 catalysts. The average size of Au–Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2–3 nm with increasing TiO2 crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H2 1 bar, 30 °C). The exertion of electronic modification of Pd by Au–Pd alloy formation depended on the TiO2 crystallite size in which it was more pronounced for Au/Pd on the larger TiO2 (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.