富氧条件下钯催化剂上氢气还原氧化氮微观反应动力学研究  

Microkinetic Analysis for the Reduction of Nitric Oxide by Hydrogen over Palladium under Lean-Burn Conditions

作　　者：杨剑斌[1] 付桂芝[1] 王树东[1] 吴迪镛[1] 

机构地区：[1]中国科学院大连化学物理研究所,辽宁大连,116023

出　　处：《催化学报》2005年第11期946-950,共5页

基　　金：科技部科研项目

摘　　要：通过单位键指标-二次指数势(UBI-QEP)方法估算反应的表观活化能进行反应机理的随机模拟,并结合实验结果研究了富氧条件下Pd基催化剂上H2还原NO的反应. 结果表明,反应的控制步骤是H2吸附活化产生H*(*表示活性位,H*表示吸附的H原子)的过程,当反应温度低于270 ℃时, H*来自基元反应O*+H*2(→←)OH*+H*,反应温度上升到310 ℃时, H*2+*(→←)2H*成为H*的主要来源. NO以(NO)*2的形式吸附在Pd催化剂表面,还原产物N2O来自两条途径,分别是(NO)*2的分解以及相邻的两个NO*分子之间的结合; N2主要来自N2O*的分解以及相邻的N*和NO*分子的结合; NH3则由中间产物HNO*经过逐步加氢生成. 富氧条件下, NO和O2之间存在吸附和反应的竞争,低温下NO在Pd表面的吸附几率远大于O2, 此时H2优先还原NO. 反应温度的升高导致各物种的吸附能力下降,其中NO的降低最明显,因此高温下催化剂表面的主要吸附物种由NO变为O2, 此时H2优先与O2反应. 在150～310 ℃范围内,实验结果和模拟数据非常吻合.Utilizing the stochastic simulation, a microkinetic model that quantitatively describes the reduction of NO by H2 on the Pd catalyst under the lean-burn conditions was developed. The parameters of elementary reaction steps were calculated by the transition state theory along with the unity bond index-quadratic exponential potential method. The rate-limiting step of the reaction is the generation of H^＊ from H2 （＊ denotes an active site and H^＊ means an adsorbed H atom）. When reaction temperature is below 270℃ , H^＊ is formed by the process O^＊ ＋ H2^＊ →← OH^＊ ＋ H^＊ When temperature rises to 310℃ the generation of H^＊ prefers to occur via the reaction H2^＊＋＊→←2H^＊ NO adsorbs on the Pd surface in a dimer form of （NO）2^＊ instead of NO^＊ The reducing product N2O comes from two routes, decomposition of （NO）2^＊ and combination of adjacent NO^＊, N2 comes from the decomposition of N2O^＊ or the combination of N^＊ and NO2^＊. When temperature is above 230℃ , little amount of N2 is formed through combination of neighboring N^＊ NH3 is produced by the gradual hydrogenation of HNO^＊ During the reduction process, there is a competition between NO and O2 in adsorption as well as reduction. NO favors to adsorb on Pd, while O2 prefers to be reduced. At low temperature, the adsorption influences the reaction predominantly, so NO can be reduced by H2 selectively. With the increase in reaction temperature, the adsorption of NO decreases gradually, and the side reaction between H2 and O2 becomes predominant. From 150℃（2 to 310 ℃ , the simulation results are in accordance with the experimental data.

关 键 词：氧化氮 氢气 钯 微观反应动力学 随机模拟 

分 类 号：O643.32[理学—物理化学]