Continuous palladium films were synthesized at controlled depths within por
ous alumina disks by Ha reduction of organopalladium compounds dissolved in
supercritical CO2 at 60 degreesC using an opposing reactants deposition ge
ometry. Film position was controlled by adjusting the relative concentratio
ns of Ha and the palladium precursor (pi -2-methylallyl(cyclopentadienyl)pa
lladium (II) or palladium(II) hexafluoroacetylacetonate) on opposite sides
of the alumina substrate. Because of a disparity in the diffusivity of the
metal precursor and Hz in the support, a temporary barrier of poly-4-methyl
-1-pentene on the H-2 Side of the alumina substrate was used to reduce Ha f
lux in a controlled manner. Guided by a simple mass transport model, Pd fil
ms between 2 and 80 mum thick were deposited at prescribed depths between 8
0 and 600 mum as measured from the precursor side. Electron probe microanal
ysis indicated complete pore filling of the porous alumina at the reaction
zone and X-ray diffraction revealed that the structure of the deposit is na
nocrystalline. The flux of Na through the alumina disk was reduced by over
4 orders of magnitude after deposition and annealing at 500 degreesC.