Quasi-homogeneous catalytic reaction and heterogeneous separation over Pd nanoparticles supported on modified poly(methyl methacrylate) with an upper critical solution temperature

Abstract

Thermoresponsive poly(methyl methacrylate) (PMMA) and EDA-modified PMMA-stabilized Pd nanoparticles were prepared and used as smart catalysts for the hydrogenation of 4-nitrophenol and hydrodechlorination (HDC) of 4-chlorophenol (4-CP) to realize the quasi-homogeneous reaction and heterogeneous separation. The catalysts were characterized via UV-visible spectroscopy, FT-IR spectroscopy and transmission electron microscopy (TEM). UV-visible spectroscopy shows that PMMA has an upper critical solution temperature (UCST) of 45.2 °C in an aqueous alcohol solution, and the EDA modification slightly increased the UCST value of the polymer. TEM characterization indicates highly dispersed Pd nanoparticles due to the stabilization by organic groups of the polymers. The kinetics study shows that the reduction of 4-nitrophenol was pseudo first order. High conversions of 4-nitrophenol and 4-chlorophenol were obtained on Pd/PMMA-EDA, which is similar to that on Pd-PVP and higher than those on Pd/PMMA and Pd/C. After the reaction, the soluble catalyst Pd/PMMA-EDA spontaneously precipitated from the solution with the decrease in temperature, and simply separated from the reaction medium for the next run. The Pd/PMMA-EDA catalyst can be reused more than three times with a slight decrease in activity.