富氧条件下氮氧化物的选择性催化还原 Ⅰ.Ag/Al_2O_3催化剂上C_3H_6选择性催化还原NO的性能

Selective Catalytic Reduction of NO in the Presence of Excess Oxygen Ⅰ.SCR of NO with C_3H_6 over Ag/Al_2O_3

利用自行研制的全自动催化剂活性评价装置和原位漫反射红外光谱仪 ,分别考察了Ag的负载量和形态、氧浓度及水蒸气添加对Ag/Al2 O3 催化剂上C3 H6选择性催化还原NO性能的影响 .结果表明 ,Ag的最佳负载量为 4 %～ 6 % ,此时粒径为 15nm左右的银簇粒子均匀地分散在Al2 O3 载体表面 .在GHSV =5 0 0 0 0h-1和θ =4 30～ 5 5 0℃条件下 ,4 %Ag/Al2 O3 上NO转化率可达 90 %以上 .反应过程中有机含氮化合物及NO2 的生成 ,导致NO和NOx 转化率间产生差异 .当氧浓度为 7%时 ,催化剂对NO选择性还原的催化活性最高 .水的添加阻碍了活性中间物种NCO及其前驱体的形成 。

The selective catalytic reduction (SCR) of NO with C 3H 6 over Ag/Al 2O 3 in excess oxygen was studied. The Ag particles could evenly be dispersed on the surface of Al 2O 3 with an optimal Ag loading of 4%～6% and an average size of 15 nm. The NO conversion over 4%Ag/Al 2O 3 catalyst was above 90% under the conditions of GHSV= 50?000 h -1 and θ =430～550 ℃. Organic nitro compounds (R ONO, R NO 2) and nitrogen dioxide formed during the SCR reaction resulted in the difference between NO and NO x conversion. The optimal NO reduction reactivity over Ag/Al 2O 3 was achieved in the presence of 7%O 2. The NO conversion decreased with the introduction of water, compared with the condition in the absence of water, because the formation of R ONO and R NO 2 and subsequently their decomposition into Ag NCO and Al NCO on the surface of Ag/Al 2O 3 were suppressed.