Theoretical Investigation of the Mechanism of the Selective Catalytic Reduction of Nitric Oxide with Ammonia on H-Form Zeolites
Theoretical Investigation of the Mechanism of the Selective Catalytic Reduction of Nitric Oxide with Ammonia on H-Form Zeolites
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DOI：
10.1021/jp806674d
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发表时间：
2008-11-06
影响因子：
3.7
通讯作者：
Keil, Frerich J.
中科院分区：
文献类型：
--
作者：
Brueggemann, Till C.;Keil, Frerich J.
利用密度泛函理论，在含有 5T 原子的 H-ZSM5 骨架的一部分（代表 H 型沸石）上研究了在氧气存在下用氨选择性催化还原 NO 的情况。该机制分为三个部分：(1) NO 氧化为 NO2，(2) 中间体 (NH2NO) 的形成，以及 (3) 该物质分解为氮和水。第二步，研究了三种不同的途径，最初存在于活性位点上的 NOx 种类不同：(i) 两个 NO 分子形成 N2O2，(ii) NO2 和 NO 形成 N2O3，以及 (iii) 两个 NO2 分子形成 N2O4。对于步骤 1 和 2，考虑了势能面的交叉来实现单分子到吸附簇的转变。对于该机理的所有三个部分，与相应的均相反应相比，多相催化反应的能量分布是有利的。由于氨在酸性位点上的强烈吸附，整个反应的速率决定步骤很可能是由于NH3阻断活性位点而将NO氧化为NO2。就本工作中我们研究的NH3选择性催化还原NO的反应机理而言，结果与实验文献相符。
The selective catalytic reduction of NO with ammonia in the presence of oxygen has been investigated on a portion of the H-ZSM5 framework which contains 5T atoms by using density functional theory, representing H-form zeolites. The mechanism was subdivided into three parts: (1) the oxidation of NO to NO2, (2) the formation of an intermediate (NH2NO), and (3) the decomposition of this species to nitrogen and water. For the second step, three different pathways were studied, differing in the NOx species initially present on the active site: (i) two NO molecules form N2O2, (ii) NO2 and NO form N2O3, and (iii) two NO2 molecules form N2O4. For steps 1 and 2, the crossing of potential energy surfaces was considered for the transition of single molecules to adsorbed clusters. For all three parts of the mechanism, the energy profile of the heterogeneously catalyzed reaction is favorable, as compared to that of the corresponding homogeneous reaction. Due to the strong adsorption of ammonia on the acid site, it is likely that the rate-determining step of the overall reaction is the oxidation of NO to NO2 caused by blocking of the active site by NH3. As far as we have investigated the reaction mechanism of the selective catalytic reduction of NO with NH3 in this work, the results are in agreement with the experimental literature.