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

摘要

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 SiO_2, ZrO_2, and CeO_2. The N_2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction with H_2 (H_2-TPR), NO chemi-sorptions, 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, Co_3O_4/CeO_2 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 Co_3O_4/CeO_2 in the presence of H,O. On the other hand, irreversible de-activation occurred over the same catalyst even in the presence of 5 ppm SO_2 in a feed. The strongly adsorbed SO_2 can prohibit NO from adsorbing on the active sites and also can prevent formed NO_2 from desorbing off the catalyst surface. The formation of SO_3 cannot be observed from the chemisorbed SO_2 on Co_3O_4/CeO_2 during TPO.