Photocatalytic hydrogenation of acetophenone over Pd–TiO2 using saccharides as hydrogen sources

Acetophenone was effectively converted to 1-phenylethanol, a hydrogenated product of acetophenone, over a Pd–TiO₂ photocatalyst using various saccharides without the use of hydrogen gas, indicating that various saccharides can be used instead of hydrogen gas in this photocatalytic hydrogenation system. Although 1-phenylethanol was formed when any saccharide was used, the use of saccharides having a hemiacetal structure such as sucrose decreased the reaction rate. This is because that reactivity of the aldehyde (formyl) group is higher in a photocatalytic system using TiO₂. Generally, the rate of the reaction is decreased when saccharides with large molecular weight, including oligosaccharides and polysaccharides, are used as substrates in the photocatalytic reaction. However, the rate of the reaction did not depend on the molecular weight of saccharides in the present photocatalytic system. Therefore, this photocatalytic system shows wide applicability of saccharides; 15 kinds of saccharides including 3 kinds of polysaccharides could be used as hydrogen sources. The results indicate the possibility of utilizing biomass for hydrogenation instead of hydrogen gas.