Tailored and recyclable ppm levels of Pd nanoparticles for chemoselective hydrogenation of nitroarenes in water

Abstract

For the first time, a hitherto unreported green synthesis of anilines by the non-loading type ppm nanopalladium-catalyzed reduction of nitro compounds is described. The reaction and post-treatment purification processes can produce high-purity target products without the use of organic solvents. The catalytic turnover frequency was as high as 27062 h⁻¹, which greater than that of the Pd/C catalyst under the same conditions. This even outperforms state-of-the-art Pd-, Pt-, and Ru-based catalysts for the nitrobenzene hydrogenation reported previously. Key to success was the design and utilization of the palladium nanoparticle with strong lipophilicity and highly stable, which permits the ppm palladium-catalyzed selective hydrogenation in water at room temperature without dispersant, providing a general preparation of functionalized anilines in good-to-high yields. The unprecedented high activity of the palladium nanoparticles is attributed to the support, which interacts strongly with the metal to maintain the oxidation–reduction states of the metals and accelerate the reaction. This work avoids the use of phase transfer reagents, as well as strong reductants, organic acids, and high-pressurized hydrogen gas as hydrogen sources, providing a promising concept for developing green catalytic systems. Benefitting from the heterogeneous manner, successful recycling in water of the catalysts was further achieved with high reaction efficiency maintained, and the total palladium leaching was less than 0.1 ppm after five cycles of the catalysts.