The effect of cobalt precursors on NO oxidation over supported cobalt oxide catalysts

The effect of cobalt precursors such as cobalt acetate and cobalt nitrate on NO oxidation was examined over cobalt oxides supported on various supports such as SiO2, ZrO2, and CeO2. The N-2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction with H-2 (H-2-TPR), NO chemisorptions, and temperature-programmed oxidation (TPO) with mass spectroscopy were conducted to characterize catalysts. The NO uptake as well as the catalytic activity for NO oxidation was dependent on the kinds of cobalt precursors and supports for supported cobalt oxides catalysts. Among tested catalysts, Co3O4/CeO2 prepared from cobalt acetate showed the highest catalytic activity. The catalytic activity generally increased with the amount of chemisorbed NO. Reversible deactivation was observed over Co3O4/CeO2 in the presence of H2O. On the other hand, irreversible deactivation occurred over the same catalyst even in the presence of 5 ppm SO2 in a feed. The strongly adsorbed SO2 can prohibit NO from adsorbing on the active sites and also can prevent formed NO2 from desorbing off the catalyst surface. The formation of SO3 cannot be observed from the chemisorbed SO2 on Co3O4/CeO2 during TPO.