Novel preparation method for supported metal catalysts using water-in-oil microemulsion and catalytic activity in various systems

A new preparation method (ME method) using water-in-oil microemulsion was developed or supported metal catalysts. Colloids presynthesized in the microemulsion were immobilized by hydrolysis of metal alkoxide on supports without aggregation of the colloid, resulting in catalysts with narrow distributions of metal particle size. The Rh particle size of Rh/SiO₂ catalysts could be controlled independently of Rh loadings by changing the synthesis conditions of the colloid such as the type of microemulsion system and synthesis temperature. Using the particle size-controlled catalysts, the dependence of the catalytic activity on Rh particle size in CO hydrogenation was studied, and the catalyst with the optimum Rh size for CO and CO₂ hydrogenation showed extremely high activity. The ME method can also control the surface area of the supports. The ME method also resulted in stronger metal-support interaction of the catalyst, so that Ni/Al₂O₃ and Fe/SiO₂ catalysts prepared by the ME method showed anomalous behavior for catalytic CH₄-steam reforming and the CO hydrogenation, respectively.