Molecular behaviour of phenol in zeolite Beta catalysts as a function of acid site presence: a quasielastic neutron scattering and molecular dynamics simulation study
Molecular behaviour of phenol in zeolite Beta catalysts as a function of acid site presence: a quasielastic neutron scattering and molecular dynamics simulation study
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DOI：
10.1039/c9cy01548e
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发表时间：
2019-12-07
影响因子：
5
通讯作者：
de Leeuw, Nora H.
中科院分区：
文献类型：
--
作者：
Hernandez-Tamargo, Carlos;O'Malley, Alexander;de Leeuw, Nora H.
采用准弹性中子散射（QENS）实验和经典分子动力学（MD）模拟研究了苯酚在酸性沸石H-β中的迁移和相互作用，以了解木质素解聚和加氢脱氧的潜在途径. QENS实验观察到各向同性的苯酚旋转与静态分子的一部分，产生旋转扩散系数在2.60 × 10（10）和3.33 × 10（10）s（-1）之间，旋转活化能为7.2 kJ mol（-1）。苯酚在酸性和全硅沸石分子筛中的分子动力学模拟证实了实验结果，其中强吸附在酸性位上的分子表现为对旋转扩散贡献最小的不移动的部分，而移动的分子产生与实验相似的旋转扩散系数。平移扩散太慢，在QENS实验的仪器时间窗口中无法检测到，这得到MD计算的大于25 kJ mol（-1）的平移活化能的支持。该研究说明了潜在的催化剂结构中的活性位点对与生物质转化相关的分子的动力学行为的影响。
Quasielastic neutron scattering (QENS) experiments complemented by classical molecular dynamics (MD) simulations at 393-443 K were employed in a study of the mobility and interactions of phenol in acidic zeolite H-Beta, to understand systems relevant to potential routes for the depolymerization and hydrodeoxygenation of lignin. QENS experiments observed isotropic phenol rotation with a fraction of static molecules, yielding rotational diffusion coefficients between 2.60 x 10(10) and 3.33 x 10(10) s(-1) and an activation energy of rotation of 7.2 kJ mol(-1). The MD simulations of phenol in the acidic and all-silica zeolite corroborate the experimental results, where molecules strongly adsorbed to the acidic sites behave as an immobile fraction with minimal contribution to the rotational diffusion, and the mobile molecules yield similar rotational diffusion coefficients to experiment. Translational diffusion is too slow to be detected in the instrumental time window of the QENS experiments, which is supported by MD-calculated activation energies of translation larger than 25 kJ mol(-1). The study illustrates the effect of active sites in potential catalyst structures on the dynamical behaviour of molecules relevant to biomass conversion.