Catalytic Performance of NO Reduction by CO over Activated Semicoke Supported Fe/Co Catalysts

Performance of NO reduction by CO is studied over activated semicoke supported Fe/Co catalysts (FeCo/ASC). The influence of oxygen and CO concentration is investigated systematically. It is found that excess CO, with a CO:NO ratio greater than 2:1, could significantly enhance NO reduction, but oxygen, even with a concentration less than 1%, could strongly inhibit NO conversion efficiency due to the oxidation of active surface metal sites. To explore the role of CO in NO reduction, reactions without CO addition are also conducted. By comparing NO reduction behavior in the presence and absence of CO, it is found that carbon support is the main reducing agent if oxygen is in great excess, even when CO is provided. At the same time, NO reduction efficiency increases at higher oxygen concentration due to the increase of surface oxygen complex. However, excess oxygen is strongly undesired because serious gasification of carbon support is inevitable. But if oxygen concentration is not very high, CO could be fed in excess to consume oxygen and excellent NO reduction could be achieved. Possible reactions over the FeCo/ASC catalyst are summarized and the onset temperatures of each reaction are also listed to figure out possible reaction condition for NO reduction. It is observed that a temperature around 200 to 250 degrees C is favorable for NO reduction by CO in the presence of oxygen because reactions relevant to CO are already active but reactions for carbon support gasification are not activated yet. A reaction mechanism is also proposed, providing some insights on the complex catalytic reactions among NO, O-2, CO, and carbon.