固体酸改性CeO_(2)基涂覆型催化剂脱硝性能研究

Study on NH3-SCR Performance of Solid Acid Modified CeO_(2)wash-coated Catalysts

燃煤与生物质燃料进行耦合掺烧是未来降低电力行业碳排放的重要路径之一。稀土脱硝催化剂以其良好的抗碱金属中毒能力,成为未来新型脱硝催化剂的重要发展方向之一。通过引入固体酸WO_(3)和Nb_(2)O_(5)氧化物对CeO_(2)结构及表面性质进行改性,显著提高了催化剂的NH_(3)-SCR反应性能。制备的系列NbO_(x)-WO_(x)/CeO_(2)(NbWCe)涂覆型工业催化剂,在GHSV=30000 h^(-1)的高空速条件下,可实现在250~450℃内NOx的转化率在80%以上,具有较宽的温度操作窗口和超过90%的N_(2)选择性。表征结果表明,尽管WO3物种导致CeO_(2)晶体的长大,降低催化剂的比表面积,但其提供更多的强酸性位,促进催化剂对NH_(3)的吸附及利用,并抑制其非选择性氧化,促使高温区SCR活性明显升高。另一方面,Nb和Ce之间的相互作用促进催化剂表面更多Ce^(3+)和活性氧物种的形成,增强对NO的氧化能力,使低温区SCR反应性能得到显著升高。因此,通过改变催化剂中WO_(3)和Nb_(2)O_(5)的比例,可实现NbWCe催化剂活性温度窗口调控,满足电厂不同的运行工况需求。

Co-combustion of coal and biomass fuels in power plants is one of the important routes to reduce CO_(2) emission in power industry.Rare earth catalysts have become promising novel NH3-SCR catalysts due to their good resistance to alkali poisoning.In this work,WO3 and Nb_(2)O_(5) were introduced to modify the structure and surface properties of CeO_(2),which promoted the SCR activity significantly.The wash-coated honeycomb catalysts were prepared and exhibited high catalytic performance with above 80%NOx conversion and above 90%N_(2) selectivity in a wide temperature window of 250-450°C.The characterization results showed that modification of WO3 promoted the growth of CeO_(2) crystallites and decreased the surface area of catalyst.However,by providing more medium strong acid sites,it improved the adsorption and utilization of NH3 in the reactions,and inhibited the non-selective oxidation of NH3,resulting in a significantly increased SCR activity at high temperatures.The synergy between Nb and Ce species promoted the formation of more surface Ce3+and active oxygen species and enhanced the oxidation and adsorption of NO,which improved the low-temperature SCR activity.In this way,the operation temperature window of ceria based catalysts can be tuned by changing the contents of WO3 and Nb_(2)O_(5),to meet the requirements of different flue gas conditions and operating requirements of power plants.