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芳香胺类化合物及其衍生物是一类重要的有机合成中间体,广泛应用于染料、农药、医药及其他精细化学品.目前催化芳香硝基化合物还原制备芳香胺的多相催化体系多使用含有d6–d10贵金属以及高活性Ni的催化剂.为了提高反应的选择性,金属纳米颗粒的尺寸控制、合金效应、金属载体强相互作用、溶剂以及添加剂的筛选等不同手段被采用.考虑到该类催化剂复杂的制备方法以及易氧化的性质,近年来稳定高效的非贵金属体系的开发得到了广泛关注.MoS_2是一类重要的高温加氢催化剂,不饱和的Mo位点(CUSMo)被认为在催化过程中起到了关键性作用.但是理论与实践已经证明,作为代表性的二维材料,MoS_2的活性位点多集中于层状结构的边楞结构处.占有最大暴露面积的基面结构因为稳定的Mo–S化学键组成在化学反应中多表现为催化惰性.通过剥离的手段可以有效提升活性位点的数目,但新增的活性位点仍然多集中于层状结构的边楞结构处而不是基面.在MoS_2与Mo O2结构中Mo–S和Mo–O的键长不同,同时S和O的配位形式也不同.可以预见的是,如果MoS_2结构中的一部分S元素被O元素取代,在这样的材料中将会出现大量缺陷以及活性CUS Mo结构.结合先前关于硫化钼材料的制备方法,我们通过部分硫化还原[Mo_7O_(24)]~6-前驱物的方法制备了氧掺杂的MoS_2材料(标记为O-MoS_2).通过XRD,XPS,Raman和EDX等表征发现,不同的Mo–O结构存在于O-MoS_2材料中.HRTEM表征结果显示,O-MoS_2表面存在着丰富的结构缺陷.EXAFS结果显示,O-MoS_2材料中可能含有四配位以及五配位的CUS Mo结构.以甲酸铵还原硝基苯为探针反应检测了CUS Mo结构.发现O-MoS_2可以在水相条件下高效催化芳香硝基化合物还原生成相应的芳香胺,且催化剂稳定,可以多次循环使用.结合对照不同催化剂的NH_3-TPD数据以及MoS_2结构模型,我们发现O-MoS_2材料中含有丰富的CUS Mo结构,这些CUS Mo结构更多地存在于材料的基面而非边楞结构.我们认为,对于该类掺杂MoS2材料的制备及结构表征将有利于拓宽MoS2催化剂从高温气相反应到温和液相反应中的应用.
Aromatic amine compounds and their derivatives are an important class of organic synthesis intermediates, widely used in dyes, pesticides, pharmaceuticals and other fine chemicals.At present, the catalytic reduction of aromatic nitro compounds to aromatic amine heterogeneous catalytic system using more containing d6-d10 noble metal and high activity Ni catalyst.In order to improve the selectivity of the reaction, the size control of the metal nanoparticles, the alloying effect, the strong interaction of the metal support, the solvent and the screening of additives and other means are taken into account. Complex preparation method and easy oxidation, the development of stable and efficient non-noble metal system has been paid much attention in recent years.MoS_2 is an important kind of high temperature hydrogenation catalyst, Unsaturated Mo site (CUSMo) is considered in the catalytic process Has played a key role.But the theory and practice have proved that, as a representative two-dimensional material, the active sites of MoS_2 are mostly concentrated in the edge of the layered structure.While the largest exposed area of the base surface structure is stable Mo-S chemical bond in the chemical reactions in the performance of the catalytic inertia. By means of stripping can effectively enhance the live However, the number of new active site is still more concentrated in the edge of the layered structure than the base structure.With MoS_2 and MoO_2 structure Mo-S and Mo-O bond length is different, while S And O. It is foreseeable that a large number of defects and active CUS Mo structures will appear in such a material if some of the S elements in the MoS 2 structure are replaced by O. In combination with the previous work on the molybdenum sulfide material O 2 -doped MoS_2 (labeled as O-MoS_2) was prepared by partially sulfidizing the [Mo_7O_ (24)] ~ 6-precursor by XRD, XPS, Raman and EDX methods. Mo-O structure exists in the O-MoS 2 material.HRTEM characterization results show that the O-MoS 2 surface is rich in structural defects.EXAFS results show that the O-MoS 2 material may contain four-coordinated and five-coordinated CUS Mo Structure.Using ammonium formate as a probe, the structure of CUS Mo was detected.The results showed that O-MoS 2 can catalyze the reduction of aromatic nitro compounds to the corresponding aromatic amines under aqueous conditions and the catalyst is stable and can be recycled many times The number of NH3-TPDs used in combination with different catalysts was compared And MoS 2 structure model, we found that the O-MoS 2 material is rich in CUS Mo structure, these CUS Mo structures are more present in the substrate rather than the edge of the material structure.We believe that for such doped MoS2 material preparation And the characterization of the structure will help broaden the application of MoS2 catalyst from high temperature gas phase reaction to mild liquid phase reaction.