CHEMISORPTION OF CHROMIUM ACETYLACETONATE ON POROUS HIGH-SURFACE-AREASILICA

Atomic layer epitaxy (ALE) reactions (i.e. saturating gas-solid reacti ons) of chromium acetylacetonate (Cr(acac)(3)) at 200-280 degrees C wi th silica preheated at 200-820 degrees C were studied by determining c hromium and carbon concentrations, recording FTIR spectra, and reactin g Cr(acac)(3) with the silylated silica surface. Cr(acac), was found t o be selectively chemisorbed to silica through reaction with the isola ted OH groups, leading to release of one acac ligand. The relatively l arge size of the supported chromium complex that formed had a highly c ontrolling effect on the amount of chromium atoms bound. In addition t o this steric hindrance, the saturation density of chromium could be f urther regulated by the preheat temperature of the silica, which deter mines the number of OH groups, and by the reaction temperature. The re action with the silylated silica surface provided a means for achievin g an even lower saturation density of chromium and confirmed that the strongly H-bonded OH groups present on silica preheated at 200 degrees C were only partly reactive. The ligands of the surface complex could be removed by water vapor and air treatment.