Matam Santhosh K, Boudjema Lotfi, Quesne Matthew G, Taylor James D, Catlow C Richard A
UK Catalysis Hub, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, OX11 0FA, UK.
Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK.
Phys Chem Chem Phys. 2025 Jan 29;27(5):2601-2614. doi: 10.1039/d4cp03761h.
Methanol adsorption isotherms of fresh f-ZSM-5 and steamed s-ZSM-5 (Si/Al ≈ 40) are investigated experimentally at room temperature under equilibrium and by grand canonical Monte Carlo (GCMC) simulations with the aim of understanding the adsorption capacity, geometry and sites as a function of steam treatment (at 573 K for 24 h). Methanol adsorption energies calculated by GCMC are complemented by density functional theory (DFT) employing both periodic and quantum mechanics/molecular mechanics (QM/MM) techniques. Physical and textural properties of f-ZSM-5 and s-ZSM-5 are characterised by diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) and N-physisorption, which form a basis to construct models for f-ZSM-5 and s-ZSM-5 to simulate methanol adsorption isotherms by GCMC. Both Brønsted and silanol hydroxyls are observed in f-ZSM-5 and s-ZSM-5 by DRIFTS; however, these species, especially Brønsted species, decreased considerably upon steam treatment in s-ZSM-5 due to dealumination. Although the total pore volume and mesoporosity increased in s-ZSM-5 as compared in f-ZSM-5, the total surface area (375 m g) of the steamed zeolite is lower than the fresh zeolite (416 m g) due to pore plugging caused by partial dislodgement of framework Al on steam treatment. Implications of the steam treatment on the methanol adsorption capacity of the zeolites are reflected in the experimental methanol adsorption isotherms, collected (in the pressure range between 0 and 12 kPa) at room temperature under equilibrium, which find that the overall methanol uptake is lower for s-ZSM-5 than for f-ZSM-5. The GCMC simulations show that the nature, location and distribution of acidic hydroxyls determine the methanol adsorption capacity, geometry and hence the isotherm profiles of f-ZSM-5 and s-ZSM-5. The GCMC simulations provide insight into the different adsorption sites and their reactivity towards methanol which paves the way not only to describe the isotherms of f-ZSM-5 and s-ZSM-5 but also offers a means to understand better the deactivation of ZSM-5 by steam (leading to dealumination) and subtle differences in surface adsorbed species on ZSM-5 procured from different sources.
在室温下，通过平衡实验和巨正则蒙特卡罗（GCMC）模拟研究了新鲜的f-ZSM-5和经蒸汽处理的s-ZSM-5（硅铝比≈40）的甲醇吸附等温线，目的是了解吸附容量、几何结构和吸附位点随蒸汽处理（在573 K下处理24小时）的变化情况。通过GCMC计算的甲醇吸附能由采用周期性和量子力学/分子力学（QM/MM）技术的密度泛函理论（DFT）进行补充。f-ZSM-5和s-ZSM-5的物理和结构性质通过漫反射红外傅里叶变换光谱（DRIFTS）和N-物理吸附进行表征，这为构建f-ZSM-5和s-ZSM-5的模型以通过GCMC模拟甲醇吸附等温线奠定了基础。通过DRIFTS在f-ZSM-5和s-ZSM-5中均观察到了布朗斯台德羟基和硅醇羟基；然而，由于脱铝作用，这些物种，尤其是布朗斯台德物种，在s-ZSM-5的蒸汽处理后显著减少。尽管与f-ZSM-5相比，s-ZSM-5的总孔体积和介孔率有所增加，但由于蒸汽处理导致骨架铝部分脱落造成孔堵塞，经蒸汽处理的沸石的总表面积（375 m²/g）低于新鲜沸石（416 m²/g）。蒸汽处理对沸石甲醇吸附容量的影响反映在室温下平衡状态下收集的实验甲醇吸附等温线中（压力范围为0至12 kPa），结果发现s-ZSM-5的总体甲醇吸附量低于f-ZSM-5。GCMC模拟表明，酸性羟基的性质、位置和分布决定了f-ZSM-5和s-ZSM-5的甲醇吸附容量、几何结构以及等温线轮廓。GCMC模拟深入了解了不同的吸附位点及其对甲醇的反应性，这不仅为描述f-ZSM-5和s-ZSM-5的等温线提供了途径，还为更好地理解蒸汽对ZSM-5的失活作用（导致脱铝）以及不同来源的ZSM-5表面吸附物种的细微差异提供了一种方法。
