Synergistic Effect between Ultrasmall Cu(II) Oxide and CuCr₂O₄ Spinel Nanoparticles in Selective Hydroxylation of Benzene to Phenol with Air as Oxidant

Phenol is an important commodity chemical, and the catalytic conversion of benzene to phenol by molecular oxygen with minimum waste production is of high significance from an academic as well as industrial point of view. We have developed a facile synthesis method for the preparation of 2–8 nm Cu­(II) oxide nanoparticles supported on CuCr₂O₄ spinel nanoparticles (with size ∼55 nm). Detailed characterization of the material was carried out by XRD, SEM, TEM, XPS, FTIR, TGA, TPR, BET surface area, XANES, and ICP-AES methods. XRD and XPS analyses revealed that the main phase is CuCr₂O₄ spinel, where a small amount of CuO is dispersed on it. The catalyst was highly active for selective oxidation of benzene to phenol with air as oxidant. The influence of reaction parameters was investigated in detail. The high catalytic performance of the catalyst is due to the ultrasmall size of Cu­(II) oxide nanoparticles and the strong synergy between ultrasmall Cu­(II) oxide and CuCr₂O₄ spinel nanoparticles that plays a pivotal role in activating air to generate active oxygen species which accomplishes benzene to phenol conversion (36%) with very high selectivity (78%) in a continuous process