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 importance of considering the distribution of heteroatom coordination modes to zeolite frameworks under reaction conditions, as well as pathways for their interconversion in the presence of reacting molecules, to obtain more robust mechanistic and kinetic interpretations of catalytic pathways in Lewis acid zeolites.

密度泛函理论计算与乙醇脱水成乙醚的动力学测量相结合，以确定沸石Beta骨架中Sn位点结构上不同形态的相对催化作用。Beta框架的结构复杂性需要用于熵和能量计算的非标准技术，包括考虑振动模式下的非谐效应，采用准谐态状态密度方法评估熵以及使用混合密度泛函来评估结合能。计算出的能量和熵用于构建微动力学模型，将其迭代精炼以识别所有对动力学和热力学敏感的反应步骤和中间体，然后再使用更高级别的方法对其进行处理。从这种分层方法获得的速率和平衡常数与在乙醇和水中测得的反应顺序非常吻合。位点平衡为锡位点之间的交换提供了证据，这些位点在与框架四配位的“封闭”构型，与框架三配位的水解形成的开放构型之间相互转换，并包含羟基配体和近端的硅烷醇基（“羟基-与乙醇反应形成的三坐标构型，产生乙氧基配体和近端的硅烷醇基团（“乙氧基开放”）。封闭的，羟基开放的和乙氧基开放的Sn位点通过不同的方式吸附乙醇，并通过不同的途径反应，结果，普遍的脱水途径取决于反应条件下Sn位点的形态。动力学模型表明，在研究的条件下（404 K，0.5–35 kPa乙醇，0.1–50 kPa水），封闭的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-乙醇二聚物和乙醇-水二聚物是唯一的动力学步骤。最丰富的表面中间体。这些结果突出了考虑在反应条件下考虑杂原子配位模式向沸石骨架的分布以及在存在反应分子的情况下它们相互转化的途径的重要性，以获得对路易斯酸沸石催化途径的更可靠的机理和动力学解释。乙醇-水二聚体是最丰富的表面中间体。这些结果突出了考虑在反应条件下考虑杂原子配位方式向沸石骨架的分布以及在存在反应分子的情况下它们相互转化的途径的重要性，以获得路易斯酸沸石中催化途径的更可靠的机理和动力学解释。乙醇-水二聚体是最丰富的表面中间体。这些结果突出了考虑在反应条件下考虑杂原子配位模式向沸石骨架的分布以及在存在反应分子的情况下它们相互转化的途径的重要性，以获得对路易斯酸沸石催化途径的更可靠的机理和动力学解释。