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采用连续浸渍法制备了一系列非贵金属稀燃NOx阱(LNT)催化剂CuO-K2CO3/TiO2,考察了Cu负载量对催化剂结构和NOx储存还原性能的影响.发现8%(w)CuO-K2CO3/TiO2催化剂的催化性能最佳,其对NOx的储存量达到1.559 mmol g–1,对NOx的还原效率高达99%,且在NOx还原过程中无副产物N2O产生.应用粉末X射线衍射(XRD),高分辩透射电子显微镜(HR-TEM),CO2程序升温脱附(CO2-TPD),扩展X射线吸收精细结构(EXAFS),氢气程序升温还原(H2-TPR)和原位漫反射红外光谱(in-situ DRIFTS)等技术详细表征了催化剂的结构.结果表明,不同Cu负载量的催化剂中,铜物种均主要以CuO相存在.铜的负载量直接影响铜物种、钾物种的存在状态,高分散的CuO相与表面K2CO3之间存在较强相互作用,这种相互作用不仅有利于NOx的储存,而且有利于增强催化剂的稳定性.in-situ DRIFTS结果表明,NOx储存过程中产生的两个负峰(1436和1563cm–1)缘于碳酸盐的分解,这间接证明了碳酸盐作为储存介质参与到NOx储存反应中.EXAFS结果表明,经过15个稀燃/富燃循环测试,催化剂中的CuO相仍保持稳定.基于以上表征结果,提出了CuO和K2CO3在催化剂表面的分布模型,并探讨了NOx储存还原的可能机理.
A series of CuO-K2CO3 / TiO2 catalysts for lean-burn NOx traps (LNT) were prepared by continuous impregnation method. The effect of Cu loading on the structure and NOx storage reduction performance of the catalysts was investigated. It was found that 8% (w) TiO2 catalyst has the best catalytic performance, the storage of NOx reaches 1.559 mmol g-1, the reduction efficiency of NOx is up to 99%, and no by-product N2O is produced during the process of NOx reduction.Powder X-ray diffraction (XRD) , HR-TEM, CO2-TPD, EXAFS, H2-TPR and in situ diffuse reflectance infrared spectroscopy in-situ DRIFTS) were used to characterize the structure of the catalyst.The results show that the copper species mainly exist in the CuO phase under different Cu loadings, and the copper loading directly affects the existence of copper species and potassium species, and the high Dispersed CuO phase and the surface of K2CO3 strong interaction between the interaction not only conducive to the storage of NOx, but also help to enhance the stability of the catalyst.In-situ DRIFTS results show that the two generated during the storage of NOx Negative peaks (1436 and 1563 cm -1) are due to carbonate Decomposition, which indirectly proved that carbonate was involved in the storage of NOx as a storage medium.EXAFS results show that after 15 lean / rich combustion cycles, the CuO phase in the catalyst remained stable.Based on the above characterization results, CuO and K2CO3 in the catalyst surface distribution model, and discusses the possible mechanism of NOx reduction.