Recyclable and effective Pd/poly(N-isopropylacrylamide) catalyst for hydrodechlorination of 4-chlorophenol in aqueous solution

A thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM) stabilized palladium nanoparticle catalyst was prepared for the hydrodechlorination (HDC) of 4-chlorophenol (4-CP) and the reduction of 4-nitrophenol (4-NP) at mild conditions in aqueous solution. The catalyst was synthesized by NaBH4 reduction method and characterized by transmission electron microscopy (TEM), UV–Visible spectroscopy and gel permeation chromatography (GPC). TEM characterization indicates the highly dispersed Pd nanoparticles (∼3 nm) on the surface of PNIPAM. UV–Visible spectroscopy exhibits a low critical solution temperature (LCST) of 34 °C for PNIPAM and the cloud-point temperature of 34.5 °C for PNIPAM–Pd catalyst in aqueous solution. The catalytic HDC of 4-CP and reduction of 4-NP followed the pseudo-first-order kinetics and the dynamic data were measured. High conversion (>95%) of 4-CP (4-NP) was obtained at the substrate/Pd molar ratio of 100:1 in the homogeneous catalytic system. After reaction, the catalyst could be precipitated and separated from reaction system by slightly increasing the temperature of aqueous solution. The PNIPAM–Pd catalyst can be reused three times with little reduction of HDC activity.