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

Abstract

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 °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, O2, CO, and carbon.

Promotional Effect of Manganese on Selective Catalytic Reduction of NO by CO in the Presence of Excess O2 over M@La–Fe/AC (M = Mn, Ce) Catalyst

“…The reaction of C(O) with an oxidized metal site (*O) that formed CO 2 and activated the metal site (*) can be used later for the reduction of NO to N 2 O or N 2 . The mechanism can be expressed as the following reactions [56]:…”

Oxidation Characteristics of the Semicoke From the Retorting of Oil Shale and Wheat Straw Blends in Different Atmospheres

“…On the other hand, the peak area of SO 2 increases with increasing O 2 volume fraction of the carrier gas from 5 to 10% since increasing O 2 favors SO 2 formation. However, the SO 2 peak area shows a slight declining trend in the combustion stage when O 2 increases from 10 to 21% because abundant O 2 also facilitates SO 2 capture through Reaction (7).…”

“…Secondly, the O 2 concentration of the mix gas can be adjusted below the 21% of air, which slows down the oxidation of shale oil. The third reason is that CO 2 in ambient gas generates a reductive atmosphere and thus reduces NOx emission [7]. And, last, the ambient gas containing a high concentration of CO 2 could promote the sulphuration of KCl in wheat straw semicoke and alleviate the high-temperature corrosion [8].…”

The influence of support composition on the activity of Cu:Ce catalysts for selective catalytic reduction of NO by CO in the presence of excess oxygen

“…14 Carbonbased materials can also be used as supports for NO x reduction by CO at low temperature (below 300 1C). 15 Yao et al 16 used Ce 0.67 Sn 0.33 O 2 , Ce 0.67 Zr 0.33 O 2 , and Ce 0.67 Ti 0.33 O 2 as supports for the preparation of copper-based catalysts for the NO + CO reaction. They found that CuO/Ce 0.67 Zr 0.33 O 2 was reduced more easily than other catalysts, most probably due to the differences in the electronegativity of the dopant.…”

“…The catalytic performance of Fe/Co catalyst over activated semicoke (ASC) for NO reduction by CO was investigated. 7,15 The catalyst revealed excellent performance under oxygen-free conditions, but due to the oxidation of active metal sites in the presence of oxygen, the NO + CO reaction was strongly inhibited; CO will be quickly consumed, and oxygen preferentially oxidizes CO over the carbon support; then, NO-carbon reaction will be the main reaction. Formation of surface oxygen compounds in the presence of oxygen could enhance the NO-carbon reaction.…”