Synthesis of size-controlled Rh nanoparticles with liquid-phase reduction method and its application in preparation of hydrogen via steam reforming of methanol

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 RhCl3 center dot 3H(2)O 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 gamma-Al2O3 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.