Deposition of Palladium Nanodots of Controlled Size and Density onto Surface-Modified SiO2 Particles by an Atmospheric Pressure CVS/MOCVD Process
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 (σg ~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.