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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。
Two catalysts, Ce Ti O x and Ce Zr Ti O x, were prepared by coprecipitation method for the selective catalytic reduction of NO x with NH 3. The effects of Zr addition on the thermal stability of CeTiO_x catalysts were investigated by thermal aging of the two catalysts at different temperatures. NH3-SCR activity data showed that Zr-modified catalysts have better catalytic activity and N2 selectivity than CeTiOx catalysts after aging at 650, 750 and 850 ℃. XRD, Raman and H 2 -TPR results show that addition of Zr can prevent Ce species from sintering and inhibit the formation of Ti O 2. The SEM image of the catalyst shows that the addition of Zr suppresses the growth of particles due to the increase of the calcination temperature. The Ce3d spectra of XPS shows that the Ce ~ (3 +) / Ce4 + ratio of the CeTiO_x catalyst decreases more significantly than that of the CeZrO_i_x catalyst as the aging temperature increases. This means that with the addition of Zr, more lattice defects and oxygen vacancies appear on the surface of the Zr-modified catalyst, which is advantageous for the improvement of the catalytic performance. In addition, NH3-TPD results show that after the same high temperature aging, the modified catalyst retains more Br? Nsted acidic sites, enhances the catalytic activity and inhibits ammonia oxidation. Therefore, the addition of Zr improves the thermal stability of the catalyst.