Catalytic hydrogenation of quinoline over recyclable palladium nanoparticles supported on tannin grafted collagen fibers

Black wattle tannin (BT), a typical natural plant polyphenol, was grafted onto collagen fiber (CF) to act as the stabilizer and carrier of Pd nanoparticles, and as a result, a recyclable heterogeneous Pd catalyst (Pd-BT-CF) was synthesized. The main physicochemical properties of the Pd-BT-CF catalyst were characterized by Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). It was found that the catalyst was in an ordered fibrous state, on which Pd nanoparticles with diameter of 4 nm were highly dispersed. Subsequently, the Pd-BT-CF catalyst was employed for the hydrogenation of quinoline. The influences of reaction time, temperature, H2 pressure and solvent on the catalytic hydrogenation of quinoline were systematically investigated. The experimental results suggested that the Pd-BT-CF catalyst exhibited high catalytic activity and selectivity for quinoline hydrogenation. The average turnover frequency (TOF) of Pd-BT-CF was as high as 165.3 mol mol−1 h−1, and the selectivity to 1,2,3,4-tetrahydroquinoline was 100% when the reaction was carried out at 60 °C and 2.0 MPa for 1.0 h. Moreover, the activity and selectivity of Pd-BT-CF catalyst were not significantly reduced after being reused 6 times, exhibiting a satisfied reusability. Further XPS, Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and TEM analyses confirmed that the Pd species were stabilized by the hydroxyls of BT-CF, which prevented the aggregation and leakage of Pd during the reaction.

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► Fibrous heterogeneous Pd catalyst.
► A highly stable and active heterogeneous Pd catalyst.
► Partial catalytic hydrogenation of quinoline.
► High activity, selectivity and reusability.