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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Molecular Origins of Selectivity in the Reduction of NO_x by NH_3
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Molecular Origins of Selectivity in the Reduction of NO_x by NH_3

机译：NH_3还原NO_x的选择性分子起源

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摘要

The fundamental principle underlying the selective catalytic reduction(SCR)of NO_x to N_2 is the promotion of reactions of reductant with NO_x over competing,and thermodynamically preferred,reactions with a large excess of O_2.A similar competition between NO_x and O_2 exists in the noncatalytic,thermal reduction of NO_x with NH_3.In this work density functional theory calculations are used to elucidate the origins of the remarkable selectivity in thermal deNO_x.Thermal deNO_x is initiated by the conversion of NH_3 into the active reductant,NH_2 radical.NH_2 radical reacts with NO at rates typical of gas-phase radical reactions to produce a relatively strongly bound-H_2NNO adduct that readily rearranges and decomposes to N_2 and H_2O.In contrast,NH_2 radical reacts exceedingly slowly with O_2:the H_2N-OO adduct is weakly bound and more readily falls apart than reacts to products.The pronounced discrimination of NH_2 against reaction with O_2 is unusual behavior for a radical but can be understood through comparison of the electronic structures of the H_2NNO and H_2NOO radical adducts.These two key elements of thermal deNO_x-reductant activation and kinetic inhibition of reactions with O_2-are similarly essential to successful catalytic lean NO_x reduction,ancj are important to consider in evaluating and modeling NO_x SCR.
机译：NO_x选择性催化还原（SCR）到N_2的基本原理是促进还原剂与NO_x的反应超过竞争，并且在热力学上优选与过量的O_2反应。在非催化反应中，NO_x和O_2之间存在相似的竞争然后用NH_3进行NO_x的热还原。在该工作密度泛函理论计算中，阐明了热deNO_x的显着选择性的起源。通过将NH_3转化为活性还原剂NH_2自由基引发了热deNO_x。NH_2自由基与NO以气相自由基反应的典型速率生成相对较强键合的H_2NNO加合物，该加合物易于重排并分解为N_2和H_2O。相比之下，NH_2自由基与O_2的反应极其缓慢：H_2N-OO加合物的键合较弱，并且更多NH_2对与O_2反应的明显区分是自由基的不寻常行为，但可以通过比较H_2NNO和H_2NOO自由基加合物的电子结构来理解。这两个重要的热deNO_x还原剂活化和与O_2反应的动力学抑制的关键要素对于成功地催化贫化NO_x还原同样至关重要，因此在评估并建模NO_x SCR。

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