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首页> 外文期刊>Journal of Catalysis >First principles, microkinetic, and experimental analysis of Lewis acid site speciation during ethanol dehydration on Sn-Beta zeolites
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First principles, microkinetic, and experimental analysis of Lewis acid site speciation during ethanol dehydration on Sn-Beta zeolites

机译：乙醇脱水在Sn-β沸石脱水过程中的第一种原理，微动素和实验分析

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Density functional theory calculations are combined with kinetic measurements of ethanol dehydration to diethyl ether to identify the relative catalytic contributions of structurally distinct speciations of Sn sites in zeolite Beta frameworks. The structural complexities of the Beta framework require nonstandard techniques for entropy and energy calculations, including consideration of anharmonic effects in vibrational modes, employment of quasi-harmonic densities of states methods to evaluate entropies, and use of hybrid density functionals to evaluate binding energies. Calculated energies and entropies are used to construct a microkinetic model that is iteratively refined to identify all kinetically and thermodynamically sensitive reaction steps and intermediates which are subsequently treated with the higher-level methods. The rate and equilibrium constants obtained from this tiered approach agree well with measured reaction orders in ethanol and water. Site balances provide evidence for the interconversion of Sn sites between “closed” configurations that are tetra-coordinated to the framework, open configurations formed by hydrolysis that are tri-coordinated to the framework and contain a hydroxyl ligand and proximal silanol group (“hydroxy-open”), and open tri-coordinate configurations formed by reaction with ethanol, yielding an ethoxy ligand and proximal silanol group (“ethoxy-open”). Closed, hydroxy-open, and ethoxy-open Sn sites adsorb ethanol via distinct modes and react via distinct pathways, with the consequence that prevalent dehydration pathways depend on the speciation of Sn sites under reaction conditions. The kinetic modeling indicates that, under the conditions studied (404?K, 0.5–35?kPa ethanol, 0.1–50?kPa water), bimolecular dehydration on the closed Sn site is the sole kinetically-relevant step, and ethanol, ethanol-ethanol dimers, and ethanol-water dimers are the most abundant surface intermediates. These results highlight the importanc
机译：密度函数理论计算与乙醇脱水的动力学测量与乙醚的动力学测量相结合，以鉴定沸石β框架中Sn位点的结构上明显凝视的相对催化贡献。 Beta框架的结构复杂性需要熵和能量计算的非标准技术，包括考虑振动模式的Anharmonic效应，各种状态的准谐波密度的就业方法评估熵，以及使用混合密度函数来评估结合能量。计算的能量和熵用于构建微酮模型，迭代地改进以鉴定所有动力学和热力学敏感的反应步骤和随后用更高级别的方法处理的中间体。从这种分层方法获得的速率和平衡常数与乙醇和水中的测量反应顺序相同。网站余额为SN位点之间的互联提供了对框架的“闭合”配置之间的互联的证据，通过水解形成的开放式配置，所述水解形成为框架，并含有羟基配体和近端硅烷醇基（“羟基 - 打开“），并通过与乙醇反应形成的打开三坐标构型，得到乙氧基配体和近端硅烷醇基（”乙氧基开放“）。通过不同的模式闭合，羟基开放和乙氧开和乙醇开放Sn位点吸附乙醇，并通过不同的途径反应，结果是普遍的脱水途径取决于在反应条件下SN位点的形态。动力学建模表明，在所研究的条件下（404 k，0.5-35 kPa乙醇，0.1-50？KPA水），闭合Sn位点上的双分子脱水是唯一的动力学相关步骤，乙醇，乙醇 - 乙醇二聚体和乙醇 - 水二聚体是最丰富的表面中间体。这些结果突出了Importanc

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