以金属氧化物及钙钛矿结构化合物为活性组分的ZSM-5催化剂上NO_x选择性还原研究

Catalytic Reduction of NO_x over Metaloxide-and Perovskite-ZSM-5 Catalysts in Presence of Water Vapour

研究了在水蒸汽存在条件下 ,以 NH3为还原剂 ,金属 /ZSM- 5催化剂和负载于 ZSM- 5上的钙钛矿结构催化剂上的 NOx 选择性催化还原 (SCR)性能 .实验结果表明 ,当反应气中通入水蒸汽时 ,各样品的催化活性均下降 ,同时伴随着 N2 选择性的增加 .而 Cu- ZSM- 5样品却表现出独特的性能 ,在所有测定样品中具有最高的 NOx转化率 (在 450℃时达到 69% ) ,当有水蒸汽存在时 ,其活性没有下降 ,反而有所增加 ,450℃时转化率达到了85% .钙钛矿结构的样品表现出一个重要特性 ,其对 NOx 的 SCR反应具有很高的 N2 选择性 ,特别在水蒸汽存在条件下 ,副产物 N2 O的选择性非常低 ,几乎为零 .其中 L a Fe O3样品的催化性能最佳 .

Selective catalytic reduction of nitrogen oxides(NO x ) from diesel engine exhausts in presence of water vapour over metaloxide and perovskite\|ZSM\|5 catalysts using ammonia as a reductant have been studied. Zeolite ZSM\|5(Si/Al=20) is a poor catalyst for the reduction of NO x with ammonia in presence of O\-2 , but when loaded with metals like Cu, Fe, Cr and Ni, it behaves as active catalysts for NO x \|reduction. Cu/ZSM\|5 shows higher activity than other metal/ZSM\|5 catalysts, both with and without water vapour. It is observed that NO x \|conversion has dropped in presence of water vapour, while the selectivity to N\-2 increase. But Cu/ZSM\|5 is an exception, its activity does not drop, but slightly increases. Peroviskites, such as LaFeO\-3/ZSM\|5, LaCoO\-3/ZSM\|5 and LaNiO\-3/ZSM\|5, prepared by coprecipitation and coated on cordierite honeycomb, show high activity for NO x \|reduction and low N\-2O formation, indicating high selectivity to N\-2. Especially in presence of water vapour, the by\|product, N\-2O, is hardly formed. This is very advantageous of NO x selective catalytic reduction, for the by\|product, N\-2O can be formed over many effective catalysts. It is probable, that according to synergetic effect, the two catalysts, Cu/ZSM\|5 and LaFeO\-3/ZSM\|5, may be combined into one efficient catalyst, Cu\|LaFeO\-3/ZSM\|5, which may possess high activity, anti\|water property and high selectivity.