Investigation Of Cylindrical Palygorskite-activated Carbon Supported Manganese Oxides Catalysts For Low-temperature Selective Catalytic Reduction（SCR） Of NO By NN₃

Coal is the main energy in China, and its combustion generates a large mount ofharmful ingredients including sulfur dioxide (SO2), nitrogen oxides (NOx) anddust. As one of the major pollutants in coal combustion flue gas, NOx can notonly damage human health but also cause ozone depletion, acid rain, green-house and photochemical smog. Therefore, control of NOx emission hasbecome one of the stringent environmental issues in China.In recent years, Selective Catalytic Reduction (SCR) of NOx has beenconsidered to be the most effective technology for reducing NOx emissions,and its core technique is the preparation of efficient and stable catalysts.Nowadays, the vanadium-based（V2O5/TiO2or V2O5-WO3/TiO2）catalysts are themain commercial available SCR catalysts and widely used for NOx emissioncontrol, which have high catalytic activity, stability and strong resistance toSO2. Meanwhile, the SCR unit is usually located at upstream of the electricprecipitation and flue gas desulfurization, and the operating temperature ofvanadium-based catalysts is often280-420oC. Since the flue gas temperature ofthe most existing boilers is usually150-200oC in our country and there is noreserve space between economizer and air preheater in existing boiler system,the commercial available vanadium-based catalysts are unsuitable for most ofthe existing boiler system in China. Thus, it is important to developlow-temperature SCR denitrification catalysts to match the existing boilersystem.In this paper, natural palygorskite (PG) and activated carbon (AC) weremixed to prepare PG-AC catalyst supports, and supported various transitionmetal oxides (Fe, Cu, Mn, V, Ni) to prepare low-temperature SCRdenitrification catalysts. The denitrification activities of the catalysts weretested in a fixed bed quartz reactor as well as the effects of preparation process(calcination temperature, the loading) and operating conditions (space velocity,O2content, calcination time). It was found that Mn-based catalysts had thehighest low-temperature SCR activity among these catalysts.Mn8/PG-AC/300oC, which contained8%Mn and was calcined at300oC in Ar),obtained a92%NO conversion at200oC with GHSV=5400h-1and3%O2. Theresults of XRD and XPS showed that the active center of Mn-based catalysts was mainly in the form of Mn2O3, and its state and dispersion were affected bycalcination temperature.Based on the Mn8/PG-AC/300oC catalyst, binary denitrification catalystsfor low-temperature selective catalytic reduction (SCR) were also studied inthis work. Several transition metals were added to the Mn8/PG-AC/300oCcatalyst and the effects were also investigated. The results showed that theaddition of Fe increased the low-temperature SCR catalytic activity, and NOconversion of Fe0.8-Mn8/PG-AC/300oC catalyst reached more than97%at200oC. Furthermore, the addition of Fe broadened reaction temperature rangeof the catalysts (100-200oC). Fe0.8-Mn8/PG-AC/300oC catalyst was a superiorcatalyst for low-temperature SCR denitrification and it had promisingindustrial application for purifying coal-fired flue gas.