A. Binder, A. Heel, G. Kasper

Chemical Vapor Deposition, 2007, 13, 48-54

 A continuous gas phase process at atmospheric pressure for tailoring Pd/SiO₂ catalyst particles is described and characterized. Emphasis is placed on controlling the size and number density of Pd nano-dots on the carrier particle surface. First, submicron SiO₂ support particles are generated continuously in a flow reactor by chemical vapor synthesis (CVS) from TEOS [tetraethyl(ortho)silicate]. 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 nm², by adjusting the synthesis conditions. In a second step, Pd nano-dots are deposited onto the SiO₂ by metal‑organic CVD of Cp(allyl)Pd [(η³‑allyl)(η⁵‑cyclopentadienyl)palladium]. The median diameter of the Pd nano-dots was varied between about 1.3 and 3 nm (σ_g ~1.2) by adjusting the precursor concentration in the gas phase. It is shown that number density of the Pd islands varied in proportion to the density of hydroxyl groups on the SiO₂ in the range of 0 to 12 Pd islands per 100 nm² of carrier particle surface.