载体平衡离子对MnOx/ZSM-5催化NH3-SCR性能影响

采用不同平衡离子（H⁺、Na⁺和NH₄⁺）的ZSM-5改性分子筛制备MnO_x/ZSM-5催化剂，研究平衡离子对氨选择催化还原（NH₃-SCR）反应活性的影响.NH₃-SCR反应结果表明，NH₄-ZSM-5为载体时，催化剂表现出优异的低温SCR活性，而H-ZSM-5为载体的催化剂则在高温范围对NO_x具有较高的转化率.XRD、TEM、BET、Raman、H₂-TPR、XPS等表征结果显示，平衡离子可明显影响MnO_x在催化剂中的分散位置以及氧化还原性质.MZ-NH₄催化剂中活性组分MnO_x分散在载体外表面，颗粒尺寸较大，主要以Mn³⁺形式存在，对NO具有较强的氧化能力，进而促进“快速SCR”反应的进行.而H-ZSM-5为载体时，MnO_x主要被限域在载体孔道内形成限域催化剂，主要以Mn⁴⁺形式存在.活性研究和表征结果证明，活性组分分散在催化剂外表面，更有利于低温SCR反应的进行.

The effect of equilibrium ion on the NH3-SCR performance of MnOx/ZSM-5catalysts

A series of MnO_x/ZSM-5 (H-ZSM-5, Na-ZSM-5 and NH₄-ZSM-5) catalysts were synthesized by wet impregnation method and their catalytic activities were investigated for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). The effect of the equilibrium ion on the catalytic performance and the physicochemical property of the samples were studied. Remarkably, the ions (H⁺, Na⁺ and NH₄⁺) greatly influenced the deNO_x ability of the catalysts. When NH₄-ZSM-5was adopted as the support, the catalyst exhibited the excellent the low-temperature SCR activity, while MZ-H catalyst showed better NO_x conversion at high temperature. The physicochemical properties of the samples were characterized using XRD, TEM, H₂-TPR, XPS, N₂ adsorption/desorption and Raman spectra. For MZ-NH₄ catalyst, MnO_x were mainly dispersed on the external surface of ZSM-5 and obvious agglomeration could be observed. In this case, Mn³⁺ oxide state was dominant in the catalyst, resulting in the strong oxidation of NO to NO₂, which consequently enhanced “fast reaction”. For MZ-H catalyst, MnO_x nanoparticles were confined in the channels of zeolite support and the available active sites were less, which was the reason for the poor catalytic activity at low temperature. The location of MnO_x nanoparticles and the redox property of MnO_x/ZSM-5 catalysts were affected by the equilibrium ion in zeolite, and the active components were dispersed on the outside of zeolite, which was benefited for the NH₃-SCR at low temperature.