Study of Monometallic Pd/TiO₂ Catalysts for the Hydrogenation of Succinic Acid in Aqueous Phase

A series of 2 wt % Pd/TiO₂ monometallic catalysts were prepared by varying some parameters, such as the nature of the precursor salt, the titania support, and the preparation method. The structural and textural properties of the catalytic systems were fully characterized by several physical and chemical techniques (inductively coupled plasma optical emission spectrometry, N₂ physisorption, H₂ chemisorption, transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, powder X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, and gas phase reaction of cyclohexane dehydrogenation). The catalytic performances were further estimated for the hydrogenation of an aqueous solution of succinic acid (SUC) performed in a batch reactor at 160 °C and under 150 bar total pressure. The results showed that all the Pd catalysts are very selective to produce γ-butyro­lactone, the first hydrogenated product. However, the rate of succinic acid conversion is a function of both the Pd dispersion and the preparation method. The deposition–precipitation method allows one to obtain the highest performing 2 wt % Pd/TiO₂ samples during SUC hydrogenation in terms of activity and stability.