Thermal Transformations of Chromium Acetylacetonate on Silica Surface

Chemical modification of a silica surface with chromium acetylacetonate (Cr(acac)3, acac = C5H7O2) was carried out from the gas phase at 190°C. This results in the formation of chromium acac species which interact with the silica surface because of hydrogen bonding between the surface hydroxyl groups and the quasi π-electron system of two acac ligands of Cr(acac)3. Ligand substitution in the chromium acac species on the silica surface pretreated at different temperatures was studied by IR spectroscopy, thermogravimetry, temperature-programmed oxidation, and chemical analysis. Water molecules and surface hydroxyl groups can replace acac ligands in the chromium acac surface species at 230 and 270°C, respectively. The oxidation of the acac ligands in air occurs at 340°C and is accompanied by conversion of Cr3+to Cr6+.