| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 103 === Selective catalytic reduction (SCR) is a widely used technology for eliminating NOx in flue gas from stationary sources. Traditional SCR used V2O5/WO3/TiO2 based catalysts, which require high operating temperatures of around 300~400℃. However, the temperature of waste gas would decrease to 150℃ after dust removal and desulfurization in order to minimize catalyst poisoning. And this leads to high energy consumption upon heating up the flue gas to above 300℃. Therefore, low temperature SCR has been an important subject of study during recent years. Most of the low temperature SCR catalysts are prepared by sol–gel, impregnation or co-precipitation method. As for spray drying method, it has not been reported in the literature for SCR catalysts.
In this study, the Mn-Fe/TiO2 catalyst was prepared by the spray drying method. The reaction conditions were as follows：500 ppm NO, 500 ppm NH3, reaction temperature of 40~300℃ and GHSV of 50,000 h-1. The experimental results showed that the best metal composition of catalyst is 20%Mn and 10%Fe deposited on TiO2 support as prepared by the spray drying method. And compared to the co-precipitation method, the catalyst prepared by the spray drying method could achieve almost 100% NO conversion at the reaction temperature of 100℃, while the catalyst prepared by the co-precipitation method could achieve only 83% NO conversion. From the results of ICP and XPS, it was observed that Mn and Fe metals could not be effectively supported on catalyst prepared by co-precipitation method, which is the reason for its relatively lower catalytic activity. In addition, the NH3-TPD results indicated that high Lewis acid sites existed on the surface of the catalyst can help to increase catalyst activity at low temperature. Moreover, it was found that at the drying temperature of 250℃ and frequency of wind velocity controller of 40Hz, the catalyst powder collection efficiency of the cyclone at the end of spray dryer could be improved.
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