采用共沉淀的方法制备了Ce Ti O_x和Ce Zr Ti O_x两种用于NH_3选择性催化还原NO_x的催化剂。两种催化剂在不同的高温条件下进行热老化以考察Zr的添加对Ce Ti O_x催化剂热稳定性的影响。NH_3-SCR活性数据显示,经过650、750和850℃的高温老化处理,Zr改性后的催化剂较Ce Ti O_x催化剂具有更好的催化活性和N2选择性。XRD、Raman和H_2-TPR结果表明添加Zr可以阻止Ce物种的烧结并且抑制金红石相Ti O_2的生成。催化剂的SEM图像显示Zr的添加可以抑制颗粒随着焙烧温度升高而产生的聚集长大。XPS的Ce3d光谱表明,随着老化温度的提升,Ce Ti O_x催化剂表面的Ce^(3+)/Ce4+比相对于Ce Zr Ti O_x催化剂下降更加明显。这意味着随着Zr的添加,更多的晶格缺陷和氧空缺出现在Zr改性催化剂的表面,这有利于催化性能的提升。另外,NH_3-TPD结果表明经过相同的高温老化,改性的催化剂保持了更多的Br觟nsted酸性位,提高了催化活性并抑制了氨的氧化。因此,Zr的添加提高了催化剂的热稳定性能。
CeTiOx and CeZrTiOx catalysts were prepared by a coprecipitation method and used for selective catalytic reduction of NOx 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 CeTiOx catalyst. The NH3‐SCR performance of the catalysts showed that the NOx removal activity of the Zr‐modified catalyst after poisoning was better than that of the CeTiOx 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 CeZrTiOx decreased more slowly than that of CeTiOx 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 CeTiOx catalyst.
