Mechanism of the selective catalytic reduction of NO by NH3 over MnOx/Al2O3 .2. Reactivity of adsorbed NH3 and NO complexes
Mechanism of the selective catalytic reduction of NO by NH3 over MnOx/Al2O3 .2. Reactivity of adsorbed NH3 and NO complexes
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DOI：
10.1006/jcat.1997.1789
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发表时间：
1997-10-01
影响因子：
7.3
通讯作者：
Bliek, A
中科院分区：
文献类型：
--
作者：
Kijlstra, WS;Brands, DS;Bliek, A
用TPRD、FTIR和阶跃响应研究了低负载量MnOx/Al_2O_3催化剂上NH_3选择性催化还原NO的反应机理。研究了吸附的NO和NH3络合物在473K以下的反应活性，FTIR表明，反应始于NH3在Lewis酸Mn3+中心的吸附，然后转化为NH2物种；在Bronsted酸中心形成的NH4+离子几乎不参与反应。NH2物种既可以与气相NO反应(Eley-RIdeal机理)，也可以与反应性亚硝酸盐中间体(Langmuir-HinShelwood机理)反应。桥联亚硝酸盐和单齿亚硝酸盐能够在这种低温下反应。O-2的作用不能简单地用表面的重新氧化来关闭催化循环来解释；O-2似乎对从吸附的NH3中提取氢和协助形成反应性亚硝酸盐都是重要的。双齿硝酸盐在NH3/NO/O-2混合气体中以较慢的速度生成，在500K以下部分失活，相反，它们在较高温度下作为SCR反应的活性中间体。在此基础上，提出了该催化剂的基本步骤反应方案。(C)1997年学术出版社。
The mechanism of the selective catalytic reduction of NO with NH3 over low loaded MnOx/Al2O3 catalysts has been investigated using TPRD, FTIR, and step-response studies with labelled components. Attention has been focused on the reactivity of the adsorbed NO and NH3 complexes, identified in the preceding paper, at reaction temperatures below 473 K. FTIR shows that the reaction starts with adsorption of NH3 on Lewis acid Mn3+ sites and its subsequent transformation to NH2 species; NH4+ ions, formed at Bronsted acid sites, hardly participate in the reaction. The NH2 species can react with both gas phase NO (Eley-Rideal mechanism) and reactive nitrite intermediates (Langmuir-Hinshelwood mechanism). Bridged nitrites and monodentate nitrites are able to react at these low temperatures. The role of O-2 cannot simply be explained by reoxidation of the surface to close the catalytic cycle; O-2 appears to be important both for H-abstraction from adsorbed NH3 and in assisting in the formation of reactive nitrites. Bidentate nitrates are formed at a slow rate in a NH3/NO/O-2 mixture and partly deactivate the catalysts at temperatures below 500 K. In contrast, they serve as reactive intermediates for the SCR reaction at higher temperatures. On the basis of these results, a reaction scheme in elementary steps is proposed for this type of catalyst. (C) 1997 Academic Press.