Theoretical analysis of hydrogen solubility in direct coal liquefaction solvents

The cyclic hydrogenation technology in a direct coal liquefaction process relies on the dissolved hydrogen of the solvent or oil participating in the hydrogenation reaction.Thus,a theoretical basis for process optimization and reactor design can be established by analyzing the solubility of hydrogen in liquefaction solvents.Experimental studies of hydrogen solubility in liquefaction solvents are challenging due to harsh reaction conditions and complex solvent compositions.In this study,the composition and content of liquefied solvents were analyzed.As model compounds,hexadecane,toluene,naphthalene,tetrahydronaphthalene,and phenanthrene were chosen to represent the liquefied solvents in chain alkanes and monocyclic,bicyclic,and tricyclic aromatic hydrocarbons.The solubility of hydrogen X(mol/mol)in pure solvent components and mixed solvents(alkanes and aromatics mixed in proportion to the chain alkanes+bicyclic aromatic hydrocarbons,bicyclic saturated aromatic hydrocarbons+bicyclic aromatic hydrocarbons,and bicyclic aromatic hydrocarbons+compounds containing het-eroatoms composed of mixed components)are determined using Aspen simulation at temperature and pressure conditions of 373–523 K and 2–10 MPa.The results demonstrated that at high temperatures and pressures,the solubility of hydrogen in the solvent increases with the increase in temperature and pressure,with the pressure having a greater impact.Further-more,the results revealed that hydrogen is more soluble in straight-chain alkanes than in other solvents,and the solubility of eicosanoids reaches a maximum of 0.296.The hydrogen solubility in aromatic ring compounds decreased gradually with an increase in the aromatic ring number.The influence of chain alkanes on the solubility of hydrogen predominates in a mixture of solvents with different mixing ratios of chain alkanes and aromatic hydrocarbons.The solubility of hydrogen in mixed aromatic solvents is less than that in the corresponding single solvents.Hydrogen is less soluble in solvent compounds containing heteroatoms than in compounds without heteroatoms.

NiMo(O)物相结构与电解水析氢反应活性的关联

在电催化析氢反应中,Ni Mo(O)催化剂在高电流密度下通常表现为极低的过电位。然而,该优异电催化性能的真正起源尚不明确。一个新的角度,即研究钼镍催化剂结构/性能演变的规律,能够帮助深入理解镍钼催化剂具有高活性的本质原因。基于此,本文详细阐述了含有结晶水的钼酸镍的脱水和氧化过程,在随后的还原处理中,该演变过程也被证实对于衍生不同的催化剂相结构具有重要作用。文中通过热重-差热分析以及程序升温氢气还原的方法探究电催化剂的特征相结构演变过程。同时,借助X射线衍射仪、拉曼光谱和高分辨透射电子显微镜分析确认催化剂物相。原位电化学X射线衍射分析提供了电催化剂在反应过程中的晶相结构。本文合成了具有不同主体相结构的钼镍催化剂:MoNi4,β-NiMoO_(4)和α-NiMoO_(4),它们的析氢反应活性具有显著差异。其中,β-NiMoO_(4)作为主体相结构的NiMoO_(4)-400air-H_(2)催化剂在碱性水还原反应中显现出最差的析氢性能;与之相比,α-NiMoO_(4)作为主体相结构的NiMoO_(4)-500air-H_(2)催化剂的活性有所提升。而从NiMoO_(4)·(n-x)H_(2)O演变得到的以MoNi4为主体结构的NiMoO_(4)-300air-H_(2)催化剂具有最优异的电催化析氢反应活性。此外,通过电化学表面积归一化的活性与几何面积归一化的活性展现出相同的趋势。本文还通过密度泛函理论计算得到不同相结构的催化剂对于水还原反应中间物种(H_(2)O、OH和H)的吸附强度以及水解离能力。该研究发现不同的物相所导致的催化剂结构差异能够引起其对析氢反应中间物种的吸附能力的差异,进而具有不同的水解离能力,最终导致不同的析氢活性。在β-NiMoO_(4)上,其最差的析氢性能可归因于对三种中间物均最弱的吸附能力,阻碍了水解离过程。而对中间物种吸附能力提升,更有利于α-NiMoO_(4)表面的水还原动力学,从而改善其析氢反应活性。相比之下,表现为相对最强中间物种吸附能力的MoNi4具有最优异的催化性能。实验中β-NiMoO_(4),α-NiMoO_(4)和MoNi_(4)的析氢性能依次提升,与理论计算中各物相所对应的水解离能垒依次降低相一致,证实了析氢活性依赖于催化剂物相结构的本质。该研究为合理设计和优化Ni Mo(O)催化剂提供参考。