THERMAL TRANSFORMATIONS OF CHROMIUM ACETYLACETONATE ON SILICA SURFACE

Chemical modification of a silica surface with chromium acetylacetonat e (Cr(acac)(3), acac = C5H7O2) was carried out from the gas phase at 1 90 degrees C. This results in the formation of chromium acac species w hich interact with the silica surface because of hydrogen bonding betw een the surface hydroxyl groups and the quasi pi-electron system of tw o acac ligands of Cr(acac)(3). Ligand substitution in the chromium aca c species on the silica surface pretreated at different temperatures w as studied by IR spectroscopy, thermogravimetry, temperature-programme d oxidation, and chemical analysis. Water molecules and surface hydrox yl groups can replace acac ligands in the chromium acac surface specie s at 230 and 270 degrees C, respectively. The oxidation of the acac li gands in air occurs at 340 degrees C and is accompanied by conversion of Cr3+ to Cr6+. (C) 1997 Academic Press.