Efficient oxidation of p-xylene to terephthalic acid by using N,N-dihydroxypyromellitimide in conjunction with Co-benzenetricarboxylate

Abstract The MOF Co-BTC (BTC = benzenetricarboxylate) has been synthesized by a hydrothermal method, and characterized by means of N2 physical adsorption, X-ray diffraction, scanning electron microscope, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The material has multiple crevices, as opposed to a pore structure, and shows high thermal stability, with Co in the divalent state. It has been used in conjunction with N,N-dihydroxypyromellitimide to catalyze the oxidation of p-xylene to terephthalic acid, the reaction conditions for which have been investigated and optimized. At 150 °C, with acetonitrile as solvent instead of acetic acid and in the absence of corrosive bromine, the conversion of p-xylene reached 100 % and the selectivity for terephthalic acid exceeded 97 %. Under the optimized conditions, Co-BTC exhibits stronger catalytic activity than cobalt(II) acetate, and maintains excellent stability during the reaction. The reaction mechanism has been deduced, and the roles of N,N-dihydroxypyromellitimide and Co-BTC as synergistic catalysts in the reaction have been clarified.