Deposition of platinum nanoparticles, synthesized in water-in-oil microemulsions, on alumina supports

Platinum nanoparticles were prepared in water-in-oil microemulsions and deposited on gamma-alumina using two different methods. In the first method, the alumina support was added to the particle suspension and the microemulsion was subsequently destabilized by addition of tetrahydrofurane, whereby the particles were deposited on the alumina support. In the other method, the platinum nanoparticles were transferred to an aqueous solution were they were redispersed by a stabilizing surfactant prior to addition of the alumina support. The size of the microemulsion droplets and of the unsupported platinum particles was in the range of a few nanometers as measured by a dynamic light scattering technique (photon correlation spectroscopy). The size of the unsupported platinum nanoparticles and of the particles deposited on alumina was studied by transmission electron microscopy. Both methods for platinum particle deposition resulted in some degree of particle agglomeration, the first probably because of too-fast destabilization of the microemulsion and the second due to inefficient redispersion of the Pt particles when transferred to the aqueous phase. All samples investigated showed high catalytic activity for CO oxidation by oxygen. The highest activity was found for those samples prepared via the redispersion method where a relatively weak interaction was achieved between the redispersed Pt particles and the alumina.