Direct nitrous oxide decomposition with CoOx-CeO2 catalysts

Abstract

The focus of the performed studies were CoOx-CeO2 oxide catalysts for nitrous oxide decomposition. All CoOx-CeO2 systems exhibit similar or higher activity than the undoped cobalt catalyst. It has been found that in temperatures up to 800°C in a N2O–Ar stream cobalt in these catalysts is in the form of Co3O4. At higher temperatures it is reduced to CoO. In a N2O–O2–Ar stream Co3O4 is the main cobalt-containing phase in the entire studied temperature range. The obtained results revealed that the activity of CoOx-CeO2 systems with a high cobalt loading increases with temperature only up to 800°C in a N2O–Ar stream. Upon further temperature increase the activity of these catalysts decreases, as in the case of the undoped cobalt catalyst. This is due to the reduction of Co3O4 to CoO. Hence, when oxygen is present in the feed and cobalt is in the form of Co3O4, the activity is higher. In contrast, the activity of catalysts with the cobalt molar ratio no greater than 0.64 is the same in both N2O–Ar and N2O–O2–Ar streams and increases with temperature in the entire studied range (700–850°C). It has been demonstrated that at 850°C in a N2O–Ar stream CoOx-CeO2 systems contain two types of CoO, which require different conditions to be oxidized. This is a result of a different strength of interaction with CeO2. It can be concluded that the activity of CoOx-CeO2 systems results from the activity of Co3O4 and of the cobalt oxide–ceria interface. The share of each component is determined by the cobalt content.