Novel preparation method for supported metal catalysts with high resistance to sintering

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1. We have developed a novel preparation method for supported metal catalysts using water-in-oil microemulsion, an ME method. In this method, Rh particles are partially embedded in SiO_2 supports because the SiO_2 supports are formed by hydrolysis of TEOS around the Rh precursor particle before being synthesized in the reverse micelle. In this work, sintering behaviors of Pt particles were investigated in Pt/Al2O3 catalysts prepared by different preparation method (ME, sol-gel and impregnation method (IMP). Pt/Al2O3 catalysts prepared by ME and sol-gel method possessed high resistance to sintering compared with the catalyst prepared by IMP method, because Pt particles were embedded in the support. Furthermore, resistance to the sintering of Pt particles was improved by pressing the catalysts at 156 MPa. For the endurance test under air flow at 700 ℃ for 12 h, the catalyst prepared using microemulsion and then pressed, the pressed ME catalyst, had greater resistance to sintering of Pt particles than the sol-gel and impregnation catalysts. The pressed ME catalyst exhibited higher activity in NO-CO reaction and maintain the high activity.2. We successfully synthesized Rh nanoparticles wholly coated by a nanometer-scale SiO2 layer ring a specific microemulsion system. The thermal stability and the catalytic activity of CO-CO reaction of SiO2-coated Rh catalyst were compared with those of the catalysts prepared by ME, sol-gel and IMP methods. In the SiO2-coated Rh catalyst, all the Rh particles were covered by the SIO2 layer and remained small even after the thermal treatment at 900 ℃ for 12 h. It is concluded that migration of Rh particles of the SiO2-coated Rh catalyst was restrained by the SiO2 layer, resulting in the highest resistance to sintering. As a result, this catalyst had the highest activity in NO reduction by CO after thermal treatment at 900 ℃ for 12 h.