可控粒径纳米Rh的液相还原法制备及其在甲醇重整制氢反应中的应用

Synthesis of Size-controlled Rh Nanoparticles with Liquid-phase Reduction Method and Its Application in Preparation of Hydrogen via Steam Reforming of Methanol

采用液相还原法 ,通过控制溶液的 p H值制备了一系列粒径可控的纳米 Rh金属粒子 ,并用 TEM和UV-Vis等技术对其进行了表征 .结果表明 ,在不同 p H值的还原溶液中得到的贵金属粒径有明显变化 .溶液碱性越强 ,还原所得金属纳米粒子的粒径越小 .当溶液 p H值为 1 3时 ,纳米 Rh粒径最小 ,为 6nm左右 .采用浸渍法将得到的纳米粒子负载于 γ-Al2 O3上 ,以甲醇重整制氢为探针反应 ,考察了负载型 Rh/γ-Al2 O3中 Rh粒子粒径与反应活性的关系 ,发现随纳米 Rh粒径的减小 ,反应转化率与氢气选择性都有明显提高 .由此可以推测 ,纳米粒子的尺寸效应是 Rh/γ-Al2 O3在重整反应中具有高活性的重要原因 .

Development of nanoparticles with well-defined size is an important aspect of nanotechnology. A simple method for preparing size-controlled Rh nanoparticles was developed on the basis of chemical reduction of RhCl_3·3H_2O with nitromethane. Adjusting pH of the solution is necessary in this method. Transmission electron microscopy and UV-Vis absorption were used to study the structure and behavior of the nanoparticles as a function of pH. The results show that pH value is critical determinant for the nanoparticles size in solution, in the case of pH=7, 9 and 11, the average size is 50, 30 and 13 nm, respectively, and with the increase of pH, the size of nanoparticles becomes smaller. As pH in solution is 13, the Rh nanoparticles is the smallest, with a particle size about 6 nm. The nanoparticles were supported on γ-Al_2O_3 by impregnation method. The activity for methanol steam reforming was investigated. The result indicates that the size of the nanoparticles strongly influences the activity and selectivity of steam reforming of methanol. Both conversions and selectivities are dependent on the particle size of Rh. When the nanoparticles become smaller, the activity of reactivity is improved obviously.