新型贵金属修饰的Ag/Al_2O-3催化剂选择性催化还原NO_x的催化性能及反应机理

Catalytic Activity of Novel Noble Metal Modified Ag/Al-2O_3 for Selective Catalytic Reduction of NO_x and Reaction Mechanism

在富氧条件下研究了几种贵金属修饰的Ag/Al2 O3 催化剂选择性催化还原 (SCR)NOx 的活性和反应机理 .催化活性实验结果表明 ,在模拟柴油机尾气的实验条件下 ,5 %Ag 0 0 1%Pd/Al2 O3 在 30 0～ 5 0 0℃范围内显示出很高的NOx 转化率 ,而Pt和Au的添加均使Ag/Al2 O3 的NOx 转化率明显降低 .原位漫反射傅里叶变换红外光谱结果显示 ,添加少量的Pd在反应过程中有利于丙烯部分氧化形成烯醇式 (C=CH-O-)活性中间物种 ,该物种对NO2 和NO-3 的反应活性很高 ,能够生成关键中间体异氰酸酯 (-NCO) ,从而加速NOx 催化还原反应 .

The selective catalytic reduction (SCR) of NO x with propene over trace noble metals (Pt, Au and Pd)-modified Ag/Al 2O 3 catalysts in excess oxygen was studied. The activity test results show that 5%Ag-0.01%Pd/Al 2O 3 has a higher NO x conversion than Ag/Al 2O 3, especially at temperatures from 300 to 500 ℃. However, the addition of Au and Pt into Ag/Al 2O 3 decreases the reaction activity. In situ diffuse reflectance infrared Fourier transform spectroscopy study suggests that the presence of Pd favors the formation of surface enolic species from the part oxidation of propene. The enolic species is very active to react with NO 2 and NO - 3 to form -NCO species, which is the key reaction intermediate in the selective catalytic reduction of NO x.