Ferrocene Adsorbed on Silica and Activated Carbon Surfaces: A Solid-State NMR Study of Molecular Dynamics and Surface Interactions
Ferrocene Adsorbed on Silica and Activated Carbon Surfaces: A Solid-State NMR Study of Molecular Dynamics and Surface Interactions
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DOI：
10.1021/acs.organomet.9b00800
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发表时间：
2020-04-13
期刊：
影响因子：
2.8
通讯作者：
Bluemel, Janet
中科院分区：
文献类型：
--
作者：
Hubbard, Patrick J.;Benzie, Jordon W.;Bluemel, Janet
在常温下，无溶剂干法研磨，二茂铁吸附在二氧化硅表面和孔内的活性碳上。虽然二茂铁在孔隙中的干吸附和平移迁移率已经在厘米尺度上建立起来，但对二茂铁分子在表面的位置到位置的运动及其相对于表面的取向几乎没有系统的了解。本论文以广泛应用于学术界和工业界的二氧化硅和活性碳为载体材料。利用变温C-13和H-2固体核磁共振和T-1弛豫时间测量，从分子水平上定量地表征了二茂铁在二氧化硅和孔内活性碳表面的动力学。所得数据表明，二茂铁分子在表面上表现出类液体行为。在具有亚单层表面覆盖层的样品中，发现了各向同性运动的分子和表面附着的二茂铁分子状态之间的快速交换。在223K和263K下，二氧化硅的表面吸附分子态的自由能为6.1kcal/mol，活性碳的自由能为6.2kcal/mol。水平取向的二茂铁分子是两种材料表面热力学上最稳定的状态。这些分子表现出CP环的快速C-5旋转，如低温C-13和H-2核磁共振所确定的那样。活性碳和二氧化硅的吸附热分别为-8.4~-7.0千卡/摩尔和-6.7千卡/摩尔，表征了二茂铁与孔表面的相互作用。结果表明，两种载体材料的二茂铁-表面相互作用都具有极性特征。
Ferrocene has been adsorbed on the surface of silica and activated carbon within the pores by dry grinding in the absence of a solvent at room temperature. While the dry adsorption and translational mobility of ferrocene within the pores are already established on the centimeter scale, there is little systematic understanding of the surface site-to-site motions of the ferrocene molecules and their orientation with respect to the surface. In this paper, silica and activated carbon, both widely applied in academia and industry as adsorbents, are used as support materials. Using variable-temperature C-13 and H-2 solid-state NMR and T-1 relaxation time measurements, the dynamics of ferrocene on the surfaces of silica and activated carbon within the pores has been quantitatively characterized on the molecular scale. The obtained data indicate that ferrocene molecules show a liquid-like behavior on the surface. Fast exchange between isotropically moving molecules and surface-attached molecular states of ferrocene has been found in samples with submonolayer surface coverages. The surface-attached molecular states have been characterized by the free energies Delta G(double dagger) of 6.1 kcal/mol for silica and Delta G(double dagger) of 6.2 kcal/mol for activated carbon at 223 and 263 K, respectively. The horizontally oriented ferrocene molecules are the most thermodynamically stable states on the surfaces of both materials. These molecules exhibit fast C-5 rotation of the Cp rings, as established by low-temperature C-13 and H-2 NMR. The interactions of ferrocene with the pore surfaces have been characterized by adsorption enthalpies measured as -8.4 to -7.0 kcal/mol and -6.7 kcal/mol for activated carbon and silica, respectively. It has been suggested that the ferrocene-surface interactions for both support materials have a polar character.