Oxygen vacancy enhanced catalytic activity of reduced Co3O4 towards p-nitrophenol reduction

With the aim of replacing noble metal-based catalysts, many efforts have been devoted to the development of highly active non-noble metal-based catalysts for the reduction of p-nitrophenol (p-NP) to p-aminophenol (p-AP) by NaBH4. As a typical transition metal oxide, pristine Co3O4 is normally considered to be poorly active towards the reduction of p-NP to p-AP. In this work, the catalytic activity of pristine Co3O4 was remarkably enhanced by a facile surface reduction with aqueous NaBH4. With the characterization results of various techniques such as XRD, TEM, H2-TPR and XPS, the enhancement in the catalytic activity was attributed to the oxygen vacancies generated during the surface reduction process. The catalytic activity of reduced Co3O4 was found to be strongly dependent on the reduction time and NaBH4 concentration used for catalyst preparation. Through the surface reduction with 0.05 mol/L aqueous NaBH4 for 40 min, the as-prepared reduced Co3O4 showed the best catalytic activity in term of the shortest induction time (<0.75 min) and highest mass-normalized rate constant (20.86 min−1 g−1 L). Furthermore, the as-prepared reduced Co3O4 displayed no obvious deactivation during the five successive cycles.