One-pot carbonization of chitosan/P123/PdCl2 blend hydrogel membranes to N-doped carbon supported Pd catalytic composites for Ullmann reactions

Abstract

Novel porous nitrogen-doped carbon supported Pd (Pd@N-C) catalytic composites were prepared by one-pot thermal carbonization of chitosan/poly(ethylene glycol)‑block‑poly(propylene glycol)‑block‑poly(ethylene glycol)/PdCl2 (CS/P123/PdCl2) blend hydrogel membranes at different temperature in N2 atmosphere. The porous structure of the Pd@N-C catalytic composite was governed by both the addition of P123 and the carbonization temperature. At highest carbonization temperature of 900 °C, the prepared Pd@N-C catalytic composite from CS/P123/PdCl2 blend membrane showed the highest specific area (SBET) of 293.7 m2/g and total volume of pores (Vtot) of 0.79 cm3/g. The chemical state of the elements of C, N, O, Pd within the Pd@N-C catalytic composites were confirmed with X-ray photoelectron spectroscopy (XPS) measurements. Raman spectrum results showed that the prepared Pd@N-C catalytic composite contained mainly disordered carbon together with some graphite carbon. Pd nanoparticles sized in 5–20 nm dispersed well on the porous matrix of the carbon. The Pd@N-C catalytic composites showed excellent activities for the Ullmann homo-coupling reactions of aromatic halides, and can be recycled for 10 times. In such one-pot carbonization process, the polymer porogen is simultaneously decomposed without further etching and removal steps, which simplifies the preparation process and is beneficial to obtain Pd@N-C catalytic composites with desirable Pd loading.