Deposition of palladium nanodots of controlled size and density onto surface-modified SiO2 particles by an atmospheric pressure CVS/MOCVD process

A continuous gas-phase process under atmospheric pressure for tailoring Pd/SiO2 catalyst particles is described and characterized. Emphasis is placed on controlling the size and number density of Pd nanodots on the surface of the carrier particle. In the first step, sub-micrometer-sized SiO2 Support particles are generated continuously in a flow reactor by chemical vapor synthesis (CVS) from tetraethyl(ortho)silicate (TEOS). A process-integrated method is described to vary the surface concentration of hydroxyl groups on the SiO2 between about 1 and 6 OH groups per nm 2, by adjusting the synthesis conditions. In a second step, Pd nanodots are deposited onto the SiO2 by metal-organic (MO)CVD of Cp(allyl)Pd [(eta(3) -allyl)(eta(5)-cyclopentadienyl)palladium]. The median diameter of the Pd nanodots was varied between about 1.3 and 3 nm (sigma(g) -1.2) by adjusting the precursor concentration in the gas phase. It is shown that the number density of the Pd islands varied in proportion to the density of hydroxyl groups on the SiO2 in the range 0-12 Pd islands per 100 nm(2) of carrier particle surface.