Inhibitory effect of oxygenated heterocyclic compounds in mesoporous catalytic materials: A pulsed-field gradient NMR diffusion study
Inhibitory effect of oxygenated heterocyclic compounds in mesoporous catalytic materials: A pulsed-field gradient NMR diffusion study
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DOI：
10.1016/j.micromeso.2017.02.033
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发表时间：
2017-02
影响因子：
5.2
通讯作者：
C. D'agostino;M. Mantle;L. Gladden
中科院分区：
文献类型：
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作者：
C. D'agostino;M. Mantle;L. Gladden
含氧杂环化合物经常被用作液相催化反应的溶剂，如在多孔氧化物催化剂上的加氢和氧化。经常有报道说，与使用碳氢化合物作为溶剂介质相比，此类化合物会抑制催化剂的活性。在这项工作中，我们利用1H脉冲场梯度(PFG)核磁共振扩散研究了1，4-二氧六环/环己烷二元混合物在介孔二氧化钛中的整个组成范围内的扩散性质，以了解固体表面对孔空间内分子输运和分子相互作用的影响。结果表明，虽然烃的扩散只受几何限制的影响，但1，4-二氧六环的扩散轮廓受催化剂孔内相互作用的影响很大，这被认为是由于1，4-二氧六环的氧原子上存在孤电子对，使分子在与固体表面接触时充当Lewis碱。这与含氧杂环化合物在用作催化溶剂或作为某些化学原料中的杂质时的抑制能力的研究结果一致。这项工作表明，可以使用1H PFG核磁共振来表征表面对分子传输的影响，从而了解液体催化反应中的催化行为。
Oxygenated heterocyclic compounds are often used as solvents in liquid-phase catalytic reactions, such as hydrogenation and oxidation over porous oxide-based catalysts. It has often been reported that such compounds inhibit catalyst activity relative to the use of hydrocarbons as the solvent media. In this work we use1H pulsed-field gradient (PFG) NMR diffusion studies to study diffusion properties of binary mixtures 1,4-dioxane/cyclohexane in mesoporous TiO2over the whole composition range in order to understand the effect of the solid surface on molecular transport and molecular interactions within the pore space. The results reveal that whilst the diffusion of the hydrocarbon is only affected by geometrical restrictions, the diffusion profile of 1,4-dioxane is highly influenced by interactions within the catalyst pore, which is thought to be due to the presence of lone electron pairs on the oxygen atoms of 1,4-dioxane, allowing the molecule to act as a Lewis base when in contact with the solid surface. This agrees with findings on the inhibitory capacity of oxygenated heterocyclic compounds when used either as solvent in catalysis or present as impurities in some chemical feedstocks. The work shows that it is possible to use1H PFG NMR in order to characterise the effect of surfaces on molecular transport and hence understand catalytic behaviour in liquid-phase catalytic reactions.