Simultaneous Removal Of NO And Mercury Over CeO₂-TiO₂ Catalyst In SCR

Energy and environment are the most important factors that could affect the development of human beings. It is well-known that coals are the main resources in China. Coal combustion not only emits traditional pollutants such as dust, SOx and NOx, but also causes mercury pollution. Mercury is a kind of toxic heavy metal, which is extremely harmful to humans. Therefore, concerns about mercury emission and its control method have risen greatly all over the world in recent years. With an increasing number of coal-fired power plants equipped with wet flue gas desulfurization(WFGD) system and selective catalytic reduction(SCR) device, it is promising to use those conventional air pollution control equipments to limit mercury emission.Plenty of researches have shown that SCR catalysts could capture and be able to promote Hg0 oxidation effectively. Based on these theories, a series of Ce-Ti catalysts with different Ce loadings were synthesized through sol-gel method, characterized by XRD, SEM and BET. SCR activity and elemental mercury removal test over Ce O2/Ti O2 were conducted on a fixed-bed reactor to see how temperature, Ce O2/Ti O2 ratio, and the ingredients in flues gas influence catalytic performance.The experimental results show that the Ce Ti catalysts synthesized by sol-gel method have far better catalytic ability than those synthesized by ultrasonic-assited impregnation method and thus later tests were all focused on Ce Ti from sol-gel method. From 200 to 500?, NO conversion increased before 400? and then began to fall, reaching the highest efficiency(91.58%) over catalyst with Ce O2/Ti O2 ratio of 0.5 at 400?.O2 is of great importance to de-NOx reaction as its increase from 0 to 4% could obviously promte NO conversion. Similarly, increasing the NH3/NO ratio also was helpful for NO conversion. By contrast, NO conversion was inhibited after SO2 and H2 O were added. In Hg0 removal test, removal efficiency would rise as the Ce O2/Ti O2 ratio increased. In presence of O2, HCl could greatly promote Hg0 removal efficiency while O2 could be absorbed on the surface of catalyst and react with Hg0. Due to the competition for active O2 on the surface of catalyst between NH3 and Hg0, SCR reaction would restrain Hg0 removal reaction. It was also found that adding Cu into Ce Ti catalyst promoted catalytic performance on both NO conversion and Hg0 removal in between low-temperature range. However, its NO conversion rate dropped dramatically after 350?. What should be noted is that H2 O could relieve this phenomenon. Different from Ce Ti catalysts, SO2 could increase Hg0 removal efficiency on Cu Ce Ti catalyst. Finally, through designed experiment it was concluded that Hg0 oxidation reaction over Ce Ti catalyst follow Eley-Rideal mechanism and reaction kinetic model was built.