Insitu DRIFTS研究NO在Cu-ZSM-5上的表面吸附及选择性催化还原

The Surface Adsorption and Selective Catalytic Reaction of NO on Cu-ZSM-5 Using In situ DRIFTS

Cu-ZSM-5分子筛催化剂选择性催化还原NO具有较好的低温活性,在613K时NO还原成N2的转化率达70·6%。原位漫反射红外光谱(Insitu DRIFTS)是研究催化剂表面吸附物种及催化机理的重要方法,应用该方法在298～773K范围原位考察了以C3H6为还原剂及富O2条件下,NO在Cu-ZSM-5催化剂上的表面吸附及选择性催化还原。认为NO在Cu-ZSM-5催化剂上还原为N2的过程中,NO以一系列NOx吸附态形式与丙稀的活化物种(CxHy或CxHyOz)反应,生成有机中间体,再进一步反应,最终生成N2。有机中间体存在一个明显的从有机胺物种到腈(或—CN)再到有机氮氧物种(R—NO2或R—ONO)的过程,催化剂表面形成有机中间物种是关键步骤,Cu的作用是促进NOx形成,O2的作用是促进C3H6活化,并且是有效产生有机-氮氧化物不可缺少的条件。

The prepared Cu-ZSM-5 catalyst presents higher activity at low temperature during the selective catalytic reduction （SCR） of NO, and the conversion from NO to N2 is 70.6% at 613 K. The in situ diffuse reflectance FTIR spectroscopy （in situ DRIFTS） is an important method for studying surface adsorption of catalyst and mechanism of catalytic reaction, and was used to study the surface adsorbed species and the selective catalytic reduction reaction of NO on Cu-ZSM-5 catalyst in the presence of propene as reductant, with excess O2 and at 298-773 K. Based on the in-situ DRIFTS, a reaction mechanism is proposed that on Cu-ZSM-5, NO is first transformed to a series of NOx surface adsorbates, then these species react with the activating species of propene （Cx Hy or CxHy Ox） to form organo-intermediates, including a process from organo-NH to organo-CN again to organo- NOx（organo-nitro or organo-nitrito）, and finally these key intermediates react to form nitrogen. The role of Cu is to promote NOx content. Propene is easily activated on Cu-ZSM-5 with oxygen, and furthermore, the presence of oxygen is necessary to form organo-NOx intermediates.