Catalytic performance and reaction mechanism of NO oxidation over Co3O4 catalysts

Co3O4 nanorods and nanoparticles were prepared and differed in the overall particle sizes and shapes, while in both cases the catalytically active (110) lattice plane was mainly exposed. The forward rate of NO oxidation of Co3O4 nanorods, stated on catalyst weight, was higher than that of Co3O4 nanoparticles. However, the turnover frequency (TOF) numbers normalized by the surface Co3+ were almost the same, indicating that NO oxidation took place over the same active sites of surface Co3+ for both catalysts. Co3O4 nanorods had a larger number of exposed active sites than nanoparticles. The dissociation of surface O2*, formed by the quasi-equilibrated reaction of O2 molecules on vacant sites (*), assisted by gaseous NO to form NO2 and surface O*, was the rate-determining step in NO oxidation. In situ FTIR spectra confirmed that abundant bridged nitrates were formed on both Co3O4 nanorods and nanoparticles.