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Local and nanoscale methanol mobility in different H-FER catalysts

机译：不同H-FER催化剂中的局部和纳米甲醇迁移率

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The dynamical behaviour of methanol confined in zeolite H-FER has been studied using quasielastic neutron scattering (QENS) and classical molecular dynamics (MD) simulations to investigate the effects of the Si/Al ratio on methanol dynamics in different Brønsted acidic FER catalysts. QENS probed methanol mobility at 273–333 K in a commercial FER sample (Si/Al = 10) at methanol saturation, and in a FER sample synthesised from naturally sourced Ghanaian kaolin (FER-GHA, Si/Al = 35–48), also at saturation. Limited mobility was observed in both samples and an isotropic rotation model could be fit to the observed methanol motions, with average mobile fractions of ∼20% in the commercial sample and ∼15% in the FER-GHA, with rotational diffusion coefficients measured in the range of 0.82–2.01 × 1011 s−1. Complementary molecular dynamics simulations were employed to investigate methanol mobility in H-FER over the same temperature range, at a loading of ∼6 wt% (close to experimental saturation) in both a fully siliceous H-FER system and one with Si/Al = 35 to understand the effect of the presence of Brønsted acid sites on local and nanoscale mobility. The simulations showed that methanol diffusivity was significantly reduced upon introduction of Brønsted acid sites into the system by up to a factor of ∼3 at 300 K, due to strong interactions with these sites, with residence times on the order of 2–3 ps. The MD-calculated translational diffusivities took place over a timescale outside the observable range of the employed QENS spectrometer, varying from 0.34–3.06 × 10−11 m2 s−1. QENS observables were reproduced from the simulations to give the same isotropic rotational motions with rotational diffusion coefficients falling in a similar range to those observed via experiment, ranging from 2.92–6.62 × 1011 s−1 between 300 and 400 K.
机译：已经研究了使用准中子中子散射（QENS）和经典分子动力学（MD）模拟研究Si/Al比率对不同BRønsted酸性FER催化剂的甲醇动力学的影响的甲醇的动力学行为。在商业FER样品（Si/Al = 10）的甲醇饱和度和从天然采购的加纳高岭土合成的FER样品中，Qens在273–333 K的甲醇迁移率（Si/Al = 10）中探测也处于饱和。在两个样品中观察到有限的迁移率，以及各向同性旋转模型可以适合观察到的甲醇运动，在商业样品中平均移动分数约为20％，在FER-GHA中约为15％，在旋转扩散系数中测得的旋转扩散系数为〜15％。范围为0.82–2.01×1011 s -1。使用互补的分子动力学模拟在同一温度范围内研究H-FER中的甲醇迁移率，在完全硅质的H-FER系统中，在约6 wt％（接近实验饱和）的负载下，Si/Al =一个。 35了解布朗斯特酸位点对局部和纳米级迁移率的影响。模拟表明，由于与这些地点的强烈相互作用，在300 K时将BrønstedAcid位点引入系统时，甲醇扩散率显着降低了约3倍，停留时间为2-3 ps。 MD计算的翻译扩散率发生在使用的QenS光谱仪的可观察范围之外的时间尺度上，从0.34–3.06×10-11 m2 s-1不等。从模拟中复制了底源可观察物，以给出相同的各向同性旋转运动，其旋转扩散系数在与通过实验观察到的范围相似，范围为2.92–6.62×1011 s -1在300至400 k之间。

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