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 use ¹H pulsed-field gradient (PFG) NMR diffusion studies to study diffusion properties of binary mixtures 1,4-dioxane/cyclohexane in mesoporous TiO₂ over 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 use ¹H PFG NMR in order to characterise the effect of surfaces on molecular transport and hence understand catalytic behaviour in liquid-phase catalytic reactions.

氧化的杂环化合物通常在液相催化反应中用作溶剂，例如在基于多孔氧化物的催化剂上进行氢化和氧化。经常有报道说，相对于使用烃类作为溶剂介质，这类化合物抑制了催化剂的活性。在这项工作中，我们使用¹ H脉冲场梯度（PFG）NMR扩散研究来研究1,4-二恶烷/环己烷二元混合物在介孔TiO _2中的扩散特性为了了解固体表面对孔隙空间内分子迁移和分子相互作用的影响，在整个组成范围内。结果表明，虽然碳氢化合物的扩散仅受几何限制，但1,4-二恶烷的扩散曲线受催化剂孔内相互作用的影响很大，这被认为是由于在碳氢化合物上存在孤电子对的缘故。 1,4-二恶烷的氧原子，使该分子与固体表面接触时可充当路易斯碱。这与关于氧化杂环化合物在催化中用作溶剂或在某些化学原料中以杂质形式存在时的抑制能力的发现是一致的。工作表明可以使用¹H PFG NMR为了表征表面对分子传输的影响，因此了解液相催化反应中的催化行为。