Reduction of N2O with CO over FeMFI zeolites:: influence of the preparation method on the iron species and catalytic behavior
Reduction of N2O with CO over FeMFI zeolites:: influence of the preparation method on the iron species and catalytic behavior
复制标题
DOI：
10.1016/j.jcat.2004.01.007
复制
发表时间：
2004-04-01
影响因子：
7.3
通讯作者：
Brückner, A
中科院分区：
文献类型：
--
作者：
Pérez-Ramírez, J;Kumar, MS;Brückner, A
采用升华法、液相离子交换法和水热合成水蒸汽活化法制备了FeMF 1分子筛，考察了其对CO还原N2 O的催化性能。这导致催化剂具有不同的性质和分布的铁物种，其特征在于通过HRTEM，UV/维斯，和EPR技术。FeZSM-5样品的一个共同点是非均质铁组成，具有显着程度的铁氧化物颗粒形式的聚集。水蒸汽活化铁硅质岩中铁的聚集被抑制，呈现出明显的孤立铁物种的均匀分布。在CO存在下，N2 O在催化剂上的转化相对于直接N2 O分解强烈加速。反应速率随CO/N2 O摩尔进料比线性增加，并且强烈依赖于所应用的制备方法。一个相关性被发现之间的馏分孤立的Fe（III）物种在所制备的催化剂和活性与CO的N2 O还原。蒸汽活化的Fe-硅沸石，主要包含孤立的铁离子在框架外的位置，显示出最高的活性每摩尔铁，而高度聚集的液体离子交换催化剂呈现出最低的活性。原位UV/维斯和EPR研究证明单核铁离子参与N2 O-CO反应，也支持寡聚体FexOy物种的参与。反应机理是铁位点依赖性的。在孤立的网站上，N2 O与CO的还原发生通过协调CO物种的Fe 3+离子。在低聚物位点上的反应通过氧化还原Fe 3 +/Fe 2+过程进行，中间形成O-自由基。(C)2004年爱思唯尔公司All rights reserved.
The reduction of N2O by CO was investigated over FeMFl zeolites prepared by different methods including sublimation, liquid ion exchange, and hydrothermal synthesis followed by steam activation. This leads to catalysts with different nature and distribution of iron species, as characterized by HRTEM, UV/vis, and EPR techniques. A common denominator in the FeZSM-5 samples is the heterogeneous iron constitution, with a significant degree of clustering in the form of iron oxide particles. Iron clustering was suppressed in steam-activated Fe-silicalite, presenting a remarkable uniform distribution of isolated iron species. In the presence of CO, the conversion of N2O over the catalysts is strongly accelerated with respect to direct N2O decomposition. The reaction rate increases linearly with the molar CO/N2O feed ratio and strongly depends oil the preparation method applied. A correlation was found between the fraction of isolated Fe(III) species in the as-prepared catalysts and the activity for N2O reduction with CO. Steam-activated Fe-silicalite, containing mostly isolated iron ions in extraframework positions, shows the highest activity per mole of iron, while the highly clustered liquid-ion-exchanged catalyst presents the lowest activity. In situ UV/vis and EPR studies evidence the participation of mononuclear iron ions in the N2O-CO reaction, and also support the involvement of oligonuclear FexOy species. The reaction mechanism is iron site dependent. Over isolated sites, the reduction of N2O with CO occurs via coordinated CO species on Fe3+ ions. The reaction over oligonuclear sites proceeds via a redox Fe3+/Fe2+ process with intermediate formation of O- radicals. (C) 2004 Elsevier Inc. All rights reserved.