Electronic factors in catalysis: the volcano curve and the effect of promotion in catalytic ammonia synthesis
Electronic factors in catalysis: the volcano curve and the effect of promotion in catalytic ammonia synthesis
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DOI：
10.1016/s0926-860x(01)00826-2
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发表时间：
2001-12-20
影响因子：
5.5
通讯作者：
Norskov, JK
中科院分区：
文献类型：
--
作者：
Dahl, S;Logadottir, A;Norskov, JK
多相催化剂的活性和选择性取决于其电子和结构性质。在许多情况下，电子性质由催化活性过渡金属和助催化剂元素的选择决定。用密度泛函理论计算了这两个因素对氨合成反应中间体和过渡态能量的影响。结果表明，N-2解离活化能与吸附态氮的结合能之间存在线性关系。将计算得到的吸附能-活化能关系与微观动力学模型相结合，可确定工业条件下氨合成活性与氮-表面相互作用能的函数关系。结果是一个火山曲线，我们说明了这种关系的非促进和碱金属促进过渡金属。我们的结论是，促进是最有效的最好的非促进催化剂，促进将始终是必不可少的，以获得最佳的氨合成催化剂。微观动力学模型的分析表明，最好的催化剂是那些具有最低的表观活化能和它们表现出的反应级数之间的两个渐近行为。(C)2001 Elsevier Science B. V.保留所有权利。
The activity and selectivity of heterogeneous catalysts are determined by their electronic and structural properties. In many cases, the electronic properties are determined by the choice of both the catalytically active transition metal and promoter elements. Density functional theory is used to calculate how these two factors affect the energies of the intermediates and transition states in the ammonia synthesis reaction. We show that a linear relationship exists between the activation energy for N-2 dissociation and the binding energy of adsorbed nitrogen. The ammonia synthesis activity under industrial conditions can be determined as a function of the nitrogen-surface interaction energy by combining the calculated adsorption energy-activation energy relation with a micro-kinetic model. The result is a volcano curve and we illustrate such relationships for both the non-promoted and alkali metal promoted transition metals. We conclude that promotion is most effective for the best non-promoted catalysts and that promotion will always be essential for obtaining an optimal ammonia synthesis catalyst. Analysis of the micro-kinetic model show that the best catalysts are those with the lowest apparent activation energies and they exhibit reaction orders between two asymptotic behaviors. (C) 2001 Elsevier Science B.V. All rights reserved.