Quasielastic Neutron Scattering and Molecular Dynamics Simulation Study on the Molecular Behaviour of Catechol in Zeolite Beta
Quasielastic Neutron Scattering and Molecular Dynamics Simulation Study on the Molecular Behaviour of Catechol in Zeolite Beta
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DOI：
10.1007/s11244-020-01400-1
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发表时间：
2020-12
影响因子：
3.6
通讯作者：
Carlos E. Hernandez-Tamargo;I. Silverwood;A. O’Malley;N. H. Leeuw
中科院分区：
文献类型：
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作者：
Carlos E. Hernandez-Tamargo;I. Silverwood;A. O’Malley;N. H. Leeuw
采用准弹性中子散射（QENS）实验和分子动力学模拟研究了393 K时邻苯二酚在Beta沸石中的动力学行为，以了解酚类单体在木质素催化转化过程中的行为。与以前研究苯酚的工作相比，这两种方法都观察到邻苯二酚中第二个OH基团的存在会显著阻碍流动性，这可以通过邻苯二酚与沸石的布朗斯特位点之间更强的氢键相互作用来解释。QENS实验的仪器时间尺度允许我们探测旋转运动，并且邻苯二酚运动最适合于各向同性旋转模型，aof为2.9 × 10 s。虽然这是在误差范围内测量苯酚，分子固定的仪器时间尺度上的分数被发现是显着较高的邻苯二酚。分子动力学模拟也显示出这种“不动性”的增加，表明邻苯二酚的长程平移扩散系数在酸性β沸石中比苯酚低7倍，在硅质材料中低3倍，进一步说明了布朗斯台德位点氢键的重要性。在从我们的模拟中再现QENS观测值以探测旋转运动时，发现两个各向同性旋转的组合适合MD计算的EISF;一种对应于儿茶酚在沸石的孔系统中的自由旋转，而第二种旋转用于近似受限的和快速的“振动”，与通过其OH基团锚定到酸位点的分子一致，其运动太快而无法通过实验观察到。
The dynamics of catechol in zeolite Beta was studied using quesielastic neutron scattering (QENS) experiments and molecular dynamics simulations at 393 K, to understand the behaviour of phenolic monomers relevant in the catalytic conversion of lignin via metal nanoparticles supported on zeolites. Compared to previous work studying phenol, both methods observe that the presence of the second OH group in catechol can hinder mobility significantly, as explained by stronger hydrogen-bonding interactions between catechol and the Brønsted sites of the zeolite. The instrumental timescale of the QENS experiment allows us to probe rotational motion, and the catechol motions are best fit to an isotropic rotation model with aof 2.9 × 10s. While thisis within error of that measured for phenol, the fraction of molecules immobile on the instrumental timescale is found to be significantly higher for catechol. The MD simulations also exhibit this increased in ‘immobility’, showing that the long-range translational diffusion coefficients of catechol are lower than phenol by a factor of 7 in acidic zeolite Beta, and a factor of3 in the siliceous material, further illustrating the significance of Brønsted site H-bonding. Upon reproducing QENS observables from our simulations to probe rotational motions, a combination of two isotropic rotations was found to fit the MD-calculated EISF; one corresponds to the free rotation of catechol in the pore system of the zeolite, while the second rotation is used to approximate a restricted and rapid “rattling”, consistent with molecules anchored to the acid sites through their OH groups, the motion of which is too rapid to be observed by experiment.