Zirconium phosphate supported copper catalyst for selective oxidation of phenol to cis, cis-muconic acid

Abstract

The selective oxidation of phenol into cis, cis-muconic acid was carried out with α-zirconium phosphate supported-copper catalysts. It has been found that a sole α-zirconium phosphate exhibited a preferential selectivity (up to 80%) towards dihydroxybenzene (Catechol/Hydroquinone=1.4:1). Moreover, the further studies indicated that α-zirconium phosphate-supported copper catalysts enable to catalyze the oxidative cleavage of catechol into high-added valuable platform molecule cis,cis-muconic acid (ccMA) by in-situ generating performic acid. A 66% conversion of phenol and 60% selectivity towards cis, cis-muconic acid were obtained under mild reaction condition (30 °C, 2 h). The detailed characterization by means of XRD, SEM, TEM, and pyridine-absorbed FT-IR techniques demonstrated that copper(II) species were highly dispersed on α-zirconium phosphate, and could be bonded with the phosphate group of the support. The forming Cu(II)-O-P linkage was proved to be catalytically active species and endowed the supported-copper catalysts with a superior recyclability. The reaction pathway involved hydroxylation of phenol to give a mixture of catechol (CL) and hydroquinone (HQ), followed by the formation of a metal-catechol complex which was then rapidly oxidized into cis, cis-muconic acid (ccMA).