Facile fabrication of TiO₂ with 3D hierarchical structure and its supported Pd catalysts for high catalytic hydrogenation performance of 4-Nitrophenol to 4-Aminophenol

TiO₂ with different morphology as supports can lead to different surface properties and catalytic activities of catalysts. Herein, we reported a novel facile evaporation-induced assisted hydrothermal approach to synthesize three-dimensional hierarchical structure TiO₂ assembled from needle flakes by using Brij-35 as the morphology-directing agent. The morphology of the prepared TiO₂ from flower-like (TiO₂-FT), sea urchin-like (TiO₂-SUT), to ball-like (TiO₂-BT), as well as the size of needle flakes, were controlled by adjusting the amount of Brij-35. These TiO₂ supported palladium catalysts were facilely prepared using a green bio-reductive method with Catalpa Fruit extract as reducing agent, where they showed remarkable catalytic activity in selective hydrogenation of 4-nitrophenol by sodium borohydride. Especially, 1 wt%Pd/TiO₂-SUT with sea urchin-like exhibited higher reaction rate constant (1.44 min⁻¹) than 1 wt%Pd/TiO₂-FT (1.08 min⁻¹) and 1 wt%Pd/TiO₂-BT (0.72 min⁻¹). Furthermore, XRD, N₂ adsorption–desorption, SEM, TEM, CO-FTIR, XPS and CO chemisorption measurements were performed to study the effects of different surface morphologies on the surface properties of catalysts. It reveals that the high catalytic performance of 1 wt%Pd/TiO₂-SUT can be attributed to its specific hierarchical structure and much higher surface area, improving the uniform dispersion of Pd nanoparticles on the support to expose extra active surface Pd atoms (Pd⁰ species) over 1 wt%Pd/TiO₂-SUT.