Co物种调控增强Co/SSZ-39催化剂的低温CH_(4)-SCR活性

Regulating Co Species over Co/SSZ-39 Catalyst to Enhance the Low-temperature CH_(4)-SCR Activity

以小孔SSZ-39分子筛为载体,采用浸渍法和离子交换法制备了不同钴(Co)含量的Co/SSZ-39催化剂,利用X射线衍射仪、透射电子显微镜、氮气吸附-脱附和氢气程序升温还原等技术对Co/SSZ-39催化剂进行表征测试,对比了不同制备方法和不同Co负载量催化剂对CH_(4)选择催化还原NO反应(CH_(4)-SCR)性能的影响.结果表明,采用离子交换法经单次离心洗涤,可以调控分子筛上Co物种的类别,制备的Co-SSZ-39-S催化剂同时富含离子态Co位点和高分散的活性CoOx物种,可以促进CH_(4)低温适度活化,提高低温条件下CH_(4)选择性还原NOx的性能.将制备的催化剂应用于CH_(4)-SCR反应,在较低反应温度(400℃),NO/CH_(4)摩尔比为1∶1时,NO转化率可达68%,CH_(4)转化率可达82%;NO/CH_(4)摩尔比为1∶2时,NO转化率为76%,CH_(4)转化率为81%,且转化率在50 h内保持稳定.该催化剂可实现NOx和CH_(4)的协同去除.

Co/SSZ-39 catalyst with different cobalt(Co)content was prepared by impregnation method and ion exchange method using small-pore SSZ-39 molecular sieve as carrier.The Co/SSZ-39 catalysts were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),nitrogen adsorption-desorption and H2 tempera-ture programming reduction(H2-TPR).The effects of different preparation methods and catalysts with different Co loads on the performance of CH_(4) selective catalytic reduction of NO(CH_(4)-SCR)were compared.The characterization results showed that the classification of Co species on SSZ-39 can be regulated by ion exchange method along with a single centrifuge washing.The Co/SSZ-39-S catalyst have both ionic Co sites and highly active CoOx species.The highly active CoOx species could promote moderate activation of CH_(4) at low temperature and improve the selective NOx reduction performance of CH_(4) at low temperature.When applied to CH_(4)-SCR reaction,the catalyst prepared by this method can achieve 68%NO conversion and 82%CH_(4) conversion at a lower reaction temperature of 400℃(the molar ratio of NO and CH_(4) is 1∶1).When the molar ratio of NO and CH_(4) is 1∶2,the catalyst can achieve 76%NO conversion and 81%CH_(4) conversion,and the conversion rate remains stable within 50 h.The catalyst can realize the collaborative removal of NOx and CH_(4).