Ni nanoparticles supported on carbon as efficient catalysts for the hydrolysis of ammonia borane

We report on the preparation of three kinds of Ni nanoparticles supported on carbon （Ni/C） and their application in the catalytic hydrolysis of ammonia borane （AB）. Three Ni/C catalysts were prepared from a Ni metal-organic framework （Ni-MOF） precursor by reduction with KBI-G calcination at 700 ℃ under Ar, and a combination of calcination and reduction, the products being denoted as Ni/C-1, Ni/C-2, and Ni/C-3, respectively. The structure, morphology, specific surface area, and element valence were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, nitrogen adsorption-desorption measurements, and X-ray photoelectron spectra （XPS）. The results demonstrate that Ni/C-1 is composed of amorphous Ni particles agglomerated on carbon, Ni/C-2 is characteristic of crystalline Ni nanoparticles （about 10 nm in size） supported on carbon with Ni oxidized on the surface, while the surface of the Ni particles in Ni/C-3 is less oxidized. The specific surface areas of Ni-MOF, Ni/C-1, Ni/C-2, and Ni/C-3 are 1239, 33, 470, and 451 m2·g-1, respectively. The catalytic hydrolysis of AB with Ni/C-3 shows a hydrogen generation rate of 834 mL-min^-1·g-1 at room temperature and an activation energy of 31.6 kJ/mol. Ni/C-3 shows higher catalytic activity than other materials, which can be attributed to its larger surface area of crystalline Ni. This study offers a promising way to replace noble metal by under ambient conditions. Ni nanoparticles for AB hydrolysis     

Effect of structural promoters on the catalytic performance of cobalt-based catalysts during natural gas decomposition to hydrogen and carbon nanotubes

Catalytic thermal decomposition of natural gas to CO/CO₂-free hydrogen production was studied over cobalt catalysts supported on Al₂O₃, MgO, and SiO₂. The physico-chemical properties of the fresh catalysts were investigated by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and surface area. In addition, the morphological structure of as-deposited carbon over the spent catalysts was characterized by transmission electron microscope (TEM), Raman spectroscopy, thermogravimetric analysis, and XRD. The obtained results proved that the catalytic activity and longevity of the cobalt-based catalysts strongly depended on the nature of the applied support. Among the catalysts tested, the Co/Al₂O₃ catalyst exhibited the highest activity and stability due to the higher dispersion and stabilization of cobalt particles because of formation of CoAl₂O₃ spinel phase. The lower activity of Co/SiO₂ catalyst is mainly attributed to the aggregation of cobalt metal particles because of weak metal–support interaction. It was observed that both type and morphological structure of deposited carbon were strictly depended on the nature of the support. TEM images revealed that multi-walled carbon nanotubes were produced over Al₂O₃- and MgO-supported catalysts, whereas both carbon nanofibers and amorphous carbon were formed over the Co/SiO₂ catalyst.     

锌基碳纳米管复合材料的界面特性及增强机理

通过复合电沉积技术制备了锌基碳纳米管复合薄膜。其中, 碳纳米管表面的锌沉积层平滑连续, 无明显界面缺陷, 与其它金属基碳纳米管复合材料相比, 这种独特的界面形貌是值得注意的。在对材料变形区的观察中发现, 在薄膜变形的过程中, 适中的结合强度将允许碳纳米管与基体发生界面脱黏, 碳纳米管被拔出基体后桥联在裂纹中。虽然界面结合受到损伤, 但是仍然可以有效地传递应力。当裂纹继续扩展, 碳纳米管石墨片层开裂, 直至完全断裂。同时, 这些桥连在裂纹中的碳纳米管趋向于向垂直于裂纹的方向滑移, 它们在基体中移动时会对基体造成一定程度的损伤。这些过程都将消耗大量的破断能, 从而起到对基体的增强效果。锌基碳纳米管复合薄膜的平均硬度由HV178.3上升至HV493.5。      

超声频率对碳纳米管结构及其负载PtRu催化剂催化活性的影响

在浓硝酸和浓硫酸混合液中,采用频率分别为25、40、60和80kHz的超声波对碳纳米管(CNTs)进行官能团化处理,运用X射线衍射(XRD)、傅立叶红外(FT-IR)、热重分析(TG)等手段,考察了超声处理对碳纳米管晶相结构、表面基团、含氧基团含量的影响.以不同超声频率处理的碳纳米管作为载体,制备了一系列碳纳米管负载PtRu催化剂,并用X射线衍射技术对催化剂的晶体结构进行了表征.采用循环伏安法(CV)测试了催化剂对甲醇电氧化反应的催化活性.结果表明,采用超声频率为60Hz处理的碳纳米管具有较高的含氧基团含量,用其作为载体制备的PtRu/CNTs60催化剂具有最佳的甲醇电氧化催化活性.