NO选择性催化还原Ce-Mn-Ti-O催化剂铈组分助催化作用

用NH3程序升温脱附(NH3-TPD)、X射线衍射(XRD)、X射线光电子能谱(XPS)、H2程序升温还原(H2-TPR)和BET表面积测试结合NO选择性催化还原(SCR)微型反应评价等方法,研究了溶胶-凝胶法制备的Ce-Mn-Ti-O复合氧化物催化剂中铈组分的助催化作用.结果表明随铈含量增加,NO转化率大幅度增加,在Ce/Mn摩尔比约0.08时达极大值,其后随铈含量进一步增加,NO转化率又逐渐下降.适量铈组分的加入对Mn-Ti-O催化剂表面酸性影响不大,但增加了催化剂活性组分Mn物种的表面浓度,提高了Mn4+物种的相对含量和Mn物种的可还原性,从而提高催化剂低温SCR活性.当Ce/Mn摩尔比超过0.08,催化剂表面的Mn组分与Ce组分可能形成无定型结构的多层聚集的Ce-O-Mn物种,导致催化剂Mn/Ti摩尔比下降和Mn物种可还原性下降,从而导致催化剂SCR活性的下降.

Promotional Effect of Cerium Oxide on the Catalytic Properties of Ce-Mn-Ti-O Catalysts for Selective Catalytic Reduction of NO

The promotional effect of cerium oxide on the catalytic properties of Ce-Mn-Ti-O composite oxide catalysts prepared by the sol-gel method was studied using NH 3 -temperature programmed desorption(NH 3 -TPD),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),H 2 -temperature programmed reduction(H 2 -TPR),and BET surface area measurements combined with microreactor tests of NO selective catalytic reduction(SCR).The results showed that the addition of a cerium oxide component remarkably increased the low-temperature SCR activity of Mn-Ti-O composite oxide catalyst. When the cerium content was increased,NO conversion increased significantly and reached a maximum around Ce/Mn molar ratio of 0.08.Further increases in the cerium content resulted in a decrease in NO conversion over the catalyst.The experimental results indicated that the addition of a cerium oxide component does not influence the surface acidity of Mn-Ti-O composite oxide catalyst,but increases the surface concentration of catalytically active Mn species,the relative content of Mn 4+ ,and the reducibility of Mn species,leading to an increase in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts.When the Ce/Mn molar ratio was greater than 0.08,the formation of amorphous multilayer Ce-O-Mn species composed of Ce and Mn species may reduce the Mn/Ti molar ratio and the reducibility of Mn species, leading to a decrease in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts.