Low temperature hydrogenation of α-angelica lactone on silica supported Pd-NiO catalysts with synergistic effect

The hydrogenation of α-angelica lactone (α-AL) was achieved under mild conditions on silica supported Pd-NiO catalysts. NiO and palladium were sequentially loaded on silica by wet-impregnation and deposition-reduction, respectively. First a series of NiO/SiO₂ supports with varying Ni contents were prepared by a wet-impregnation method with Ni(NO₃)₂ as the precursor followed by calcination in air. Then a minute amount of palladium (0.2 wt%) was loaded by a deposition-reduction method using NaBH₄ as a reducing reagent. The Pd-NiO catalysts were characterized by nitrogen adsorption, XRD, H₂-TPR, XPS and TEM. The NiO were heterogeneously dispersed on silica with particle sizes ranging from 10 to 50 nm, whereas Pd was finely loaded with a diameter less than 5 nm. Nanoscale intimacy between Pd and NiO was noticed by HRTEM, resulting in high catalytic activity in liquid phase hydrogenation of α-angelica lactone to γ-valero lactone (GVL) under mild conditions. 0.2Pd-9.9NiO/SiO₂ showed the best activity among all the catalysts investigated, with 82% conversion and 100% selectivity to GVL within several minutes at 30 °C and 0.3-1 MPa H₂ pressure.