Efficient Sm modified Mn/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperature
Efficient Sm modified Mn/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperature
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DOI：
10.1016/j.apcata.2020.117413
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发表时间：
2020-02-25
影响因子：
5.5
通讯作者：
Xiang, Jun
中科院分区：
文献类型：
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作者：
Liu, Lijun;Xu, Kai;Xiang, Jun
提出了一系列Sm修饰的Mn/TiO2催化剂，用于NH3选择性催化还原NO，并对其低温催化活性进行了评价。采用XRD、低温N-2吸附、XPS、NH3-TPD、H-2-TPR等手段综合研究了Sm对Mn-Sm/TiO2催化活性的影响。结果表明：超声浸渍法制备的20Mn-10Sm/TiO2催化剂在110 ~ 250℃的温度范围内，气体时空速为80000 h(-1)， NOx转化率高于80%；弱Lewis酸位点和氧化还原能力可能是催化性能的关键性能，这是由于Mn4+和表面化学吸附氧的增加，以及Sm加入后Mn、Sm和Ti之间的相互作用增强而导致的弱酸位点。采用原位DRIFTS实验研究了其表面反应对NH3和NO的吸附。结果表明，Mn/TiO2催化剂表面的SCR反应遵循Langmuir-Hinshelwood和ely - rideal机理，其中桥接硝酸盐是重要的中间体。而在20Mn-10Sm/TiO2催化剂表面上的反应只符合Eley-Rideal机理，因为Sm的引入抑制了NH3存在下NO的吸附，从而改变了反应路径。此外，20Mn-10Sm/TiO2催化剂上的SCR反应速度快，这是由于在20Mn-10Sm/TiO2催化剂表面形成了大量的-NH2物质，使得N-H键的断裂比Sm改性催化剂更容易，这有利于20Mn-10Sm/TiO2催化剂在低温下的SCR活性。TG-DSC-MS结果表明，Sm的加入降低了Mn/TiO2催化剂的硫化作用。
A series of Sm modified Mn/TiO2 catalysts were proposed for selective catalytic reduction of NO with NH3 and their catalytic activity was evaluated at low temperature. The effect of Sm on the catalytic activity of Mn-Sm/TiO2 was comprehensively studied using XRD, low-temperature N-2 adsorption, XPS, NH3-TPD and H-2-TPR. The results showed that the 20Mn-10Sm/TiO2 catalyst, prepared by ultrasonic impregnation, exhibited NOx conversion of higher than 80 % at the temperature range of 110-250 degrees C with a gas hourly space velocity of 80,000 h(-1). The weak Lewis acid site and redox ability may be crucial properties for catalytic performance as a result of the increase of Mn4+ and surface chemisorption oxygen as well as weak acid sites due to the enhanced interaction among Mn, Sm and Ti after addition of Sm. The in situ DRIFTS experiments were conducted to investigate the adsorption of NH3 and NO with their surface reaction. The results revealed that the SCR reactions on the surface of Mn/TiO2 catalyst follow both Langmuir-Hinshelwood and Eley-Rideal mechanism and bridging nitrate is the important intermediate. While, that on surface of 20Mn-10Sm/TiO2 catalyst comply with only Eley-Rideal mechanism, as the introduction of Sm changes the reaction path by inhibiting the adsorption of NO in the presence of NH3. Besides, SCR reaction rate over 20Mn-10Sm/TiO2 catalyst is fast as a result of large amount of -NH2 species formed on the surface of 20Mn-10Sm/TiO2 catalyst for the breaking of N-H bonds become easier over the Sm modified catalyst, which is beneficial for SCR activity of 20Mn-10Sm/TiO2 catalyst at low temperature. The TG-DSC-MS results revealed that the addition of Sm reduce the sulfation of Mn/TiO2 catalyst.