Selective catalytic oxidation of benzene to phenol by a vanadium oxide nanorod (Vnr) catalyst in CH3CN using H2O2(aq) and pyrazine-2-carboxylic acid (PCA)†
Vanadium based catalysts are known to be highly efficient for oxidation reactions using O2 and/or H2O2. In this study, we developed a vanadium catalyst that can be prepared by a reaction of VCl3 in acetonitrile with the addition of 35% hydrogen peroxide (H2O2). The catalyst was further characterized by a variety of methods including 51V NMR, XRD, XPS, XAS, EA, ICP-AES, BET, SEM and TEM. Based on the results obtained, the catalyst was identified as a vanadium oxide material (Vnr) with the morphology and shape of a nanorod with dimensions of ∼40 nm × 450 nm (width × length). The porosity of a material can be essential for small molecule activation on a heterogeneous surface. This material exhibits exceptional catalytic performance for the selective oxidation of benzene to phenol (PhOH) at room temperature using H2O2 as an oxidant in acetonitrile. The addition of pyrazine-2-carboxylic acid (PCA) as a co-catalyst can efficiently enhance the catalytic activity with a percentage selectivity of 87–99% phenol, producing p-benzoquinone (p-BQ) as a minor product. With the deployment of H218O2, we observed the product phenol to be highly enriched by 18O, indicating that the hydroperoxo-vanadium intermediate is essential for its catalytic conversion. Together with its high NIH shift ratio (80% deuterium remained) observed with the mechanistic probe of 4-[2H0,1]toluene, the results suggested that the catalytic oxidation reaction mediated by Vnr may involve metal based oxygenated intermediates for its highly selective catalytic oxidation of benzene to phenol.