VO_x/ZrO_2和K-VO_x/ZrO_2催化剂的结构与催化碳黑氧化性能

The Structures of VO_x/ZrO_2 and K-VO_x/ZrO_2 Catalysts and Their Catalytic Perfo rmances for Diesel Soot Oxidation

采用等体积浸渍法制备两个系列不同V和K负载量的VOx/ZrO2和K-VOx/ZrO2催化剂.利用程序升温氧化反应(TPO)技术对VOx/ZrO2和K-VOx/ZrO2催化碳黑氧化的活性进行了考察.实验结果表明,当催化剂中V的负载量nV/nZr=4/100时,VOx/ZrO2催化剂的活性最好.添加K能显著改善VOx/ZrO2催化剂的活性,当K的添加量为nK∶nV∶nZr=1∶4∶100时,碳黑氧化的反应温度最低.催化剂的红外光谱和紫外-可见光谱表征的结果表明,nV/nZr=4/100时,催化剂的表面形成聚合的V物种浓度最大.由于聚合的V物种具有较强的氧化还原能力,因而能显著地降低柴油碳黑的氧化温度.当K-VOx/ZrO2催化剂中nK/nV超过1/4时,由于形成KVO3物种,催化剂表面原子的移动性减弱,因而催化活性降低.

Two systems of VOx/ZrO2 and K-VOx/ ZrO2 catalysts with different compositions were prepared by incipient-wetness impregnation method. The catalytic performances of these catalysts for diesel soot catalytic oxidation were investigated with temperature-programmed oxidation reaction(TPO). The results showed that the catalytic properties of the VOx/ZrO2 catalysts depend on the VOx concentration. The VOx/ZrO2 catalyst has the best activity for soot oxidation when n(V): n(Zr) is 4: 100. The VOx/ZrO2 and K-VOx/ZrO2 catalysts were characterized by FT-IR and UV-Vis. The results revealed that the highest concentration of polymerized vanadyl species presented on the surfaces of the VOx/ZrO2 catalysts when n(V): n(Zr) = 4: 100. The polymerized vanadyl can lower the oxidation temperature of diesel soot because they have very strong redox abilities. The addition of potassium to VOx/ ZrO2 catalysts can improve the catalytic activities for soot oxidation apparently. When n(K): n(V): n(Zr) = 1: 4: 100, the catalyst K-VOx/ZrO2 has the best activity for soot oxidation, i.e., the lowest reaction temperature. But the catalytic activity of the K-VOx/ ZrO2 catalysts decreased when n(K): n(V) > 1: 4, which is due to the formation of KVO3 whose surface atoms mobility is much weaker than that of polymeric VOx specie and dispersed potassium oxide.