O'Malley Alexander J, García Sakai Victoria, Silverwood Ian P, Dimitratos Nikolaos, Parker Stewart F, Catlow C Richard A
Department of Chemistry, Materials Chemistry, University College London, Third Floor, Kathleen Lonsdale Building, Gower Street, London, WC1E 6BT, UK.
ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK.
Phys Chem Chem Phys. 2016 Jun 29;18(26):17294-302. doi: 10.1039/c6cp01151a.
The diffusion of methanol in zeolite HY is studied using tandem quasielastic neutron scattering (QENS) experiments and molecular dynamics (MD) simulations at 300-400 K. The experimental diffusion coefficients were measured in the range 2-5 × 10(-10) m(2) s(-1) and simulated diffusion coefficients calculated in the range of 1.6-3.2 × 10(-9) m(2) s(-1). Activation energies were measured as 8.8 and 6.9 kJ mol(-1) using QENS and MD respectively. Differences may be attributed predominantly to the experimental use of a dealuminated HY sample, containing significant defects such as strongly adsorbing silanol nests, compared to a perfect simulated crystal containing only evenly distributed Brønsted acid sites. Experimental and simulated diffusivities measured in this study are lower than those obtained from those previously calculated in siliceous faujasite, due to methanol H-bonding to Brønsted acid sites as observed in the MD simulations. However, both experimental and simulated diffusivities were significantly higher than those obtained in NaX, due to the higher concentration of extraframework cations present in the previously studied structures.
在300 - 400 K的温度下，使用串联准弹性中子散射（QENS）实验和分子动力学（MD）模拟研究了甲醇在HY沸石中的扩散。实验测得的扩散系数在2 - 5×10⁻¹⁰ m² s⁻¹范围内，模拟计算得到的扩散系数在1.6 - 3.2×10⁻⁹ m² s⁻¹范围内。使用QENS和MD分别测得的活化能为8.8和6.9 kJ mol⁻¹。差异可能主要归因于实验中使用的脱铝HY样品，与仅包含均匀分布的布朗斯台德酸位点的完美模拟晶体相比，该样品含有大量缺陷，如强吸附硅醇巢。本研究中测得的实验和模拟扩散率低于先前在硅质八面沸石中计算得到的扩散率，这是由于在MD模拟中观察到甲醇与布朗斯台德酸位点形成氢键。然而，由于先前研究结构中存在较高浓度的骨架外阳离子，实验和模拟扩散率均显著高于在NaX中获得的扩散率。
