制备条件对柴油车用V2O5-WO3/TiO2催化剂催化性能的影响

摘要

采用偏NH4VO3和TiO2为前驱体制备选择性催化还原(SCR)催化剂涂层所需浆料,分别以分步涂覆法和一步涂覆法将浆料浸涂在蜂窝陶瓷载体上,得到了整体涂覆式选择性催化还原催化剂.对草酸添加量、焙烧时间及V2O5含量对催化活性的影响进行了研究,结果表明,V2O5(4%)-WO3/TiO2(450℃,3 h)和V2O5(5%)-WO3/TiO2(450℃,2 h)催化剂活性最优,新鲜催化剂的NO起燃温度(T50)分别为195℃和205℃,在270℃,NO转化率接近100%;操作窗口(≥80%转化率)相对较宽,分别为(225～500)℃和(230～485)℃;当V2O5负载量较小时,V2O5主要以等轴聚合的钒基型式V3O7和V6O13存在,钒基为催化剂活性中心,当V2O5负载质量分数较大(超过6%)时,V2O5主要以结晶相存在,催化作用较小.%Monolith coating selective catalytic reduction(SCR) catalysts V2O5-WO3/TiO2 were prepared with one step and two step coating methods, using ceramic honeycomb as the carriers and NH4VO3 and TiO2 as the precursors. The influence of oxalic acid dosage, V2O5 loading and calcination time on the activity of V2O5-WO3/TiO2 catalysts were investigated. The results showed that V2O5 (4％)-WO3/TiO2 (450 ℃, 3 h) and V2O5 (5％)-WO3/TiO2 (450 ℃ ,2 h)exhibited the highest catalytic activity. NO lightoff temperature ( T50 ) of the fresh catalysts were 195 ℃ and 205 ℃ , respectively and NO conversion was near 100％ at 270 ℃. NO conversion of over 80％ was attained over V2O5 (4％)-WO3/TiO2 (450 ℃ ,3 h)and V2O5(5％)-WO3/TiO2(450 ℃ ,2 h ) catalysts at (225 -500) ℃ and (230-485) ℃ ,respectively.V2O5 in V2O5-WO3/TiO2 catalysts with lower vanadium loading existed in the form of V3O7 and V6O13,which were the catalytic active centres; V2O5 in the catalysts with vanadium loading of over 6％ mainly existed in the form of crystalline phase, which had lower catalytic activity.