【摘要】 氮氧化物（NO_x）是造成大气污染的主要来源之一,严重威胁人类的身体健康.选择性催化还原（SCR）技术由于其独特的优势而受到青睐.但SCR催化剂容易受到SO₂的侵蚀而失活,使用寿命降低.开发具有抗硫能力强的高活性催化剂已成为脱硝技术研究的热点.核壳结构催化剂由于其独特的外壳结构能有效地减少活性物质与SO₂的接触,减少催化剂中毒,延长催化剂的使用寿命.而水热合成法能有效控制催化剂的外形结构,动力学外裹法能将物质均匀分布在被包裹物质的表面,两者结合有利于核壳结构催化剂的合成.本文采用两步法（水热法+动力学外包裹法）制备的MnO_x@TiO₂纳米棒核壳结构低温脱硝催化剂具有高活性、高稳定性和优异的N2选择性.此外,与MnO_x,TiO₂和MnO_x/TiO₂等纳米材料相比,MnO_x@TiO₂具有更好的SO₂和H2O抗性,表明MnO_x@TiO₂具备良好的运用前景.采用TEM,HR-TEM,XRD,Raman,BET,XPS,NH3-TPD和H2-TPR等方法对催化剂进行了系统的表征.TEM和HR-TEM结果表明,MnO_x@TiO₂表现出明显的核壳结构,且TiO₂颗粒均匀分布在MnO_x纳米棒上.XRD和Raman结果发现MnO_x@TiO₂中含有MnO₂,从而保证了MnO_x@TiO₂具有良好的脱硝活性.同时,BET,NH3-TPD和H2-TPR等结果表明,MnO_x@TiO₂具有丰富的中孔结构和路易斯酸位点,以及强氧化还原能力,因而其催化性能提高.根据SO₂侵蚀后的XPS结果,MnO_x@TiO₂与MnO_x/TiO₂相比,两者中的S元素含量差异小,但前者中的Mn4+降低量远少于后者.表明MnO_x@TiO₂的核壳结构可以在SO₂存在条件下有效地保护活性位点,因而具有更强的SO₂抗性更多还原

【Abstract】 In this study,a MnO_x@TiO₂ core-shell catalyst prepared by a two-step method was used for the low-temperature selective catalytic reduction of NO_x with NH3.The catalyst exhibits high activity,high stability,and excellent N2 selectivity.Furthermore,it displays better SO₂ and H2 O tolerance than its MnO_x,TiO₂,and MnO_x/TiO₂ counterparts.The prepared catalyst was characterized systematically by transmission electron microscopy,high-resolution transmission electron microscopy,X-ray diffraction,Raman,BET,X-ray photoelectron spectroscopy,NH3 temperature-programmed desorption and H2 temperature-programmed reduction analyses.The optimized MnO_x@TiO₂ catalyst exhibits an obvious core-shell structure,where the TiO₂ shell is evenly distributed over the MnO_x nanorod core.The catalyst also presents abundant mesopores,Lewis-acid sites,and high redox capability,all of which enhance its catalytic performance.According to the XPS results,the decrease in the number of Mn4+ active centers after SO₂ poisoning is significantly lower in MnO_x@TiO₂ than in MnO_x/TiO₂.The core-shell structure is hence able to protect the catalytic active sites from H2 O and SO₂ poisoning.更多还原