煅烧温度对Mn/TiO_2催化剂催化NO氧化活性的影响

以浸渍在二氧化钛上的锰基催化剂为对象,研究了制备过程中煅烧温度对锰基催化剂催化NO氧化活性的影响。结果表明,较低的煅烧温度有利于提高Mn/TiO2催化剂对于NO氧化的催化效率。利用X射线粉末衍射(XRD)、场发射扫描电子显微镜(FESEM)、X射线光电子能谱(XPS)、H2程序升温还原(H2-TPR)和O2程序升温脱附(O2-TPD)等表征手段研究了煅烧温度影响Mn/TiO2催化剂催化活性的作用机理。结果表明,在NO氧化过程中发挥主要作用的是Mn2O3,较低的煅烧温度有利于提高Mn2O3在锰氧化物中所占的比例,同时增加锰氧化物在载体表面的分散度,从而改善催化剂活性;当煅烧温度超过500℃时,催化剂会发生烧结,载体TiO2的晶形开始由锐钛型向金红石型转变,Mn2O3也从非晶相向晶相转变。H2-TPR和O2-TPD测试结果表明,低温煅烧有利于提高催化剂的还原性能和表面化学吸附态O2-的脱附性能,良好的还原性能和脱附性能的相互作用使催化剂表面的氧有较好的移动能力,从而促进催化剂的活性。

Influence of calcination temperature on the catalytic activity of Mn/TiO2 for NO oxidation

The influence of calcination temperature on the catalytic activity of Mn-based catalysts impregnated on TiO₂ for the oxidation of NO was studied. The results showed that, relatively low calcination temperature was beneficial to promote the catalytic activity of Mn/TiO₂ catalysts. The catalysts were characterized by various techniques to study the influence mechanism of calcination temperature, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), H₂ temperature programmed reduction (H₂-TPR) and O₂ temperature programmed desorption (O₂-TPD). It could be concluded that Mn₂O₃ played a dominant role in the process of NO oxidation, and the relatively lower calcination temperature could enhance the percentage of Mn₂O₃ in MnO_x, as well as promote the dispersion of MnO_x on TiO₂, thus raising the catalytic activity of Mn/TiO₂. When the calcination temperature was higher than 500 ℃, the agglomeration began to appear, and the crystalline phase of TiO₂ was transformed from anatase to rutile, Mn₂O₃ was, as well, transformed from amorphous phase to crystalline phase. The test results of H₂-TPR and O₂-TPD showed that relatively lower calcination temperature was beneficial to the reduction ability of Mn/TiO₂ catalysts and the desorption of chemisorbed O^2- on catalysts surface, the interaction of the two factors resulted in good mobility of chemisorbed O^2- on catalysts surface, which was good for the activity of catalysts.