Cr-CeO_x Mixed-oxide Catalysts For The Selective Catalytic Reduction（SCR） Of NO_x With NH₃ At Medium-low Temperature

According to statistics in 2014,there are about 94,000 industrial stoves, such as ceramic kiln and glass furnace, is one of the main sources of nitrogen oxides(NOx) emissions, about 4 million tons/year. Selective catalytic reduction(SCR) is widely used for removal of NOx. The characteristics of industrial kiln flue gas are the high concentration of SO2 and NOx, and low gas temperature(200-300 oC). Whereas, the traditional SCR denitrification catalyst’s operating temperature is usually high(about 300-450 oC), and with a narrow temperature window, that makes it not appropriate for denitrification condition of industrial kiln flue gas. With an eye to the situation that lack of industrial kiln flue gas denitrification technology, the development of catalysts with good SCR activity and high SO2 resistance at middium- low temperature will have good theoretical, environmental, economic and practical significance.In this paper, combinatorial chemistry was adopted for the construction of a principal catalyst library including 36 kinds of metal oxides or mixed metal oxides catalysts prepared by the solid phase method and their activities and SO2 resistance for medium- low temperature SC R of NOx were evaluated. The NOx conversion could get over 90% in the whole temperature range(180-300 oC), and reached the maximum NOx conversion of 100% at 220 °C. In situ DRIFTS and some other characterization methods were used to study the NH3-SCR fundamental principle and mechanism. It was found that the amorphous chromia on the catalyst would be connected to the catalyst’s superior activity, and the reaction could follow Eley-Rideal, the NH3(ad) adsorbed on Lewis acid site and NH4+ adsorbed on Br?nsted acid site catalyst both take place in NH3-SCR on Cr(0.4)-CeOx.Meanwhile, the SO2 tolerance of these catalysts was also investigated. NOx conversion could still reach 82% when 100 ppm SO2 was feeded at 240 oC with a GHSV=50000 h-1 after 450 min. It was to discover that the main formation and deposition on catalyst was(NH4)2SO4 when SO2 was feeded which could destroy the catalysts’ Lewis acid cite. However, because of Ce, Cr(0.4)-CeOx could reduce the thermal stability of(NH4)2SO4 on the catalyst and show good resistance to SO2.