【摘要】 CeTiO_x具有高的NH₃选择性催化还原（NH₃-SCR）活性和N₂选择性,被认为是具有应用前景的催化剂.但是,CeTiO_x不抗碱金属中毒,在含有大量K离子的生物质柴油的燃烧装置中中毒尤为严重,因而限制了CeTiO_x催化剂在生物质燃料装置上的进一步应用.本文通过在CeTiO_x催化剂中掺杂Zr元素来提升其抗K⁺中毒的能力.采用共沉淀法制备了CeTiO_x（CT）和CeZrTiO_x（ZCT）两种NH₃-SCR催化剂.将不同含量的硝酸钾（K⁺/Ce=0.1,0.2）负载在催化剂表面,焙烧处理后得到K⁺中毒的催化剂（K0.1-CT,K0.2-CT,K0.1-ZCT和K0.2-ZCT）.通过测定各催化剂的催化活性来研究Zr的添加对CT催化剂抗K⁺中毒能力的影响.NH₃-SCR活性数据表明,CT和ZCT催化剂都达到了接近100%的NO_x转化率,且两种新鲜催化剂的催化性能基本无差别.浸渍不同含量的K⁺之后,ZCT催化剂明显优于CT催化剂:K0.1-CT和K0.1-ZCT上的NO_x转化率分别为90%和62%;而K0.2-CT和K0.2-ZCT上分别为48%和13%.可见,随K⁺添加,ZCT催化剂活性降低更缓慢,表明Zr的添加提高了CT催化剂抗K⁺中毒能力.BET数据显示,在新鲜催化剂中,Zr的添加增加了催化剂比表面积和孔体积;K⁺中毒之后,ZCT仍然表现出比CT更好的织构性能.X射线衍射和拉曼光谱结果显示,随着K⁺负载量的增加,锐钛矿TiO₂的衍射峰逐渐变得尖锐,说明无定形TiO₂逐渐结晶并不断长大,从而导致催化剂比表面积下降.与CT相比,随着K⁺负载量增加,催化剂晶型并没有明显变化.这说明Zr的添加可以抑制锐钛矿TiO₂的结晶及长大.由此可见Zr的添加可抑制因K⁺中毒而引起的催化剂结构变化,所以仍能保持较高的NO_x转化率.透射电镜（TEM）结果表明,随着K⁺负载量逐渐增加,催化剂的晶粒尺寸逐渐变大:CT,K0.1-CT和K0.2-CT的平均晶粒尺寸分别为7,13和15nm,而ZCT催化剂晶粒尺寸增大并不明显,分别为5,8和10nm.很明显,Zr的添加抑制了催化剂晶粒长大,从而提高了其结构稳定性能.综上可见,由负载KNO₃而引起的"熔盐效应"得到了有效抑制.X射线光电子能谱结果表明,随着K⁺负载量增加,CeZrTiO+x催化剂的Ce³⁺/Ce⁴⁺值下降得比CeTiO_x更缓慢,说明加入Zr之后,催化剂具有更多的晶格缺陷和氧空缺,因而有利于NH₃-SCR活性的提高.另外,催化剂酸性也是影响NH₃-SCR活性的关键因素.NH₃程序升温脱附结果显示,Zr的添加可以使CeTiO_x催化剂在K⁺中毒之后仍保持较高的酸性,即Zr的添加抑制了K⁺对催化剂表面酸性的巨大破坏作用.综上可知,Zr的添加提升了CeTiO_x催化剂抗K⁺中毒能力.更多还原

【Abstract】 CeTiO_x and CeZrTiO_x catalysts were prepared by a coprecipitation method and used for selective catalytic reduction of NO_x by NH₃（NH₃-SCR）. Various amounts of KNO₃ were impregnated on the catalyst surface to investigate the effects of Zr addition on the K⁺-poisoning resistance of the CeTiO_x catalyst. The NH₃-SCR performance of the catalysts showed that the NO_x removal activity of the Zr-modified catalyst after poisoning was better than that of the CeTiO_x catalyst. Brunau-er-Emmett-Teller data indicated that the Zr-containing catalyst had a larger specific surface area and pore volume both before and after K⁺ poisoning. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy showed that Zr doping inhibited anatase TiO₂ crystal grain growth, i.e., the molten salt flux effect caused by the loaded KNO₃ was inhibited. The Ce 3d X-ray photoelectron spectra showed that the Ce³⁺/Ce⁴⁺ ratio of CezRTiO_x decreased more slowly than that of CeTiO_x with increasing K⁺ loading, indicating that Zr addition preserved more crystal defects and oxygen vacancies; this improved the catalytic performance. The acidity was a key factor in the NH₃-SCR performance; the temperature-programmed desorption of NH₃ results showed that Zr doping inhibited the decrease in the surface acidity. The results suggest that Zr improved the K⁺-poisoning resistance of the CeTiO_x catalyst.更多还原