The molecular copper complex tetrakis(acetonitrile)copper(I) perchlorate [Cu(CH3CN)(4)ClO4] (1) was shown to act as a catalyst precursor for the efficient oxidation of benzene to p-benzoquinone (p-BQ) with a percentage selectivity of 60-80% under mild conditions, and produces phenol (PhOH) as a minor product at room temperature. Here, we obtained evidences showing the formation of copper based nanoparticle catalyst (NC) (2) from 1 to be the vital step responsible for its ability to catalyze the conversion of benzene to p-BQ presumably via double oxidation. Addition of a considerable amount of H2O to the reaction mixture improved the selectivity for forming p-BQ to 84% and/or the conversion efficiency to 98%. In addition, the copper NC easily formed in situ through the oxidation of substrate using H2O2 in CH3CN. After separating the NC from the reaction mixture and recycling them several times, it still maintained comparable catalytic efficiency and selectivity for the conversion of benzene to p-BQ. (C) 2019 Elsevier Inc. All rights reserved.