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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Methanol Oxidative Dehydrogenation on Oxide Catalysts: Molecular and Dissociative Routes and Hydrogen Addition Energies as Descriptors of Reactivity
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Methanol Oxidative Dehydrogenation on Oxide Catalysts: Molecular and Dissociative Routes and Hydrogen Addition Energies as Descriptors of Reactivity

机译：氧化物催化剂上的甲醇氧化脱氢：分子和解离途径和加氢能作为反应性的表征

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The oxidative dehydrogenation (ODH) of alkanols on oxide catalysts is generally described as involving H-abstraction from alkoxy species formed via O—H dissociation. Kinetic and isotonic data cannot discern between such routes and those involving kinetically-relevant H-abstraction from undissociated alkanols. Here, we combine such experiments with theoretical estimates of activation energies and entropies to show that the latter molecular routes prevail over dissociative routes for methanol reactions on polyoxometalate (POM) clusters at all practical reaction temperatures. The stability of the late transition states that mediate H-abstraction depend predominantly on the stability of the O—H bond formed, making H-addition energies (HAE) accurate and single-valued descriptors of reactivity. Density functional theory-derived activation energies depend linearly on HAE values at each O-atom location on clusters with a range of composition (H3PMo_(12), H4SiMo_(12), H3PW_(12), H1PV1Mo_(11), and H4PV1W_(11)); both barriers and HAE values reflect the lowest unoccupied molecular orbital energy of metal centers that accept the electron and the protonation energy of O-atoms that accept the proton involved in the H-atom transfer. Bridging O-atoms form O—H bonds that are stronger than those of terminal atoms and therefore exhibit more negative HAE values and higher ODH reactivity on all POM clusters. For each cluster composition, ODH turnover rates reflect the reactivity-averaged HAE of all accessible O-atoms, which can be evaluated for each cluster composition to provide a rigorous and accurate predictor of ODH reactivity for catalysts with known structure. These relations together with oxidation reactivity measurements can then be used to estimate HAE values and to infer plausible structures for catalysts with uncertain active site structures.
机译：通常将烷醇在氧化物催化剂上的氧化脱氢（ODH）描述为涉及从通过OH离解形成的烷氧基中进行H提取。动力学和等渗数据无法区分这些路线与那些涉及与动力学相关的从未离解烷醇中提取H的路线。在这里，我们将此类实验与活化能和熵的理论估计值结合起来，表明在所有实际反应温度下，后者的分子路线优于多金属氧酸盐（POM）簇上甲醇反应的解离路线。过渡态的稳定状态主要介导H-抽象，主要取决于所形成的O-H键的稳定性，从而使H-加成能（HAE）成为反应性的精确和单值描述符。密度泛函理论推导的活化能线性依赖于具有一定范围组成（H3PMo_（12），H4SiMo_（12），H3PW_（12），H1PV1Mo_（11）和H4PV1W_（11）的簇上每个O原子位置的HAE值））;势垒和HAE值都反映了接受电子的金属中心的最低未占据分子轨道能和接受参与H原子转移的质子的O原子的质子能。桥接的O原子形成比末端原子更强的O-H键，因此在所有POM簇上均显示出更高的HAE负值和更高的ODH反应性。对于每种簇组成，ODH转化率反映了所有可及的O原子的平均反应活性HAE，可以对每种簇组成进行评估，以为结构已知的催化剂提供精确而准确的ODH反应性预测指标。然后可以将这些关系与氧化反应性测量结果一起用于估计HAE值，并推断具有不确定活性位点结构的催化剂的合理结构。

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