TPD‐MS and IR Studies of Cr(acac)3 Binding Upon CVD at Silica and Alumina Surfaces

The mechanism of CVD of Cr(acac)(3) molecules at active sites on the surface of silica and alumina supports is studied by infrared (IR) spectroscopy and temperature programmed desorption mass spectrometry (TPD-MS). TPD-MS patterns of the molecular acetylacetone [H3CCOCH2COCH3](+center dot) (m/z 100), as well as the fragment ions [H3CCOCH2CO](+) (m/z 85) and [H3CCO](+) (m/z 43), are monitored to study the interaction of acetylacetonate ligands with the support surface upon thermal treatment. It is found that surface hydroxyl groups are responsible for the binding of Cr(acac)(3) molecules, only in the case of the silica support, due to hydrogen bonding (H-bonding) with the acetylacetonate ligand. The TPD-MS of Cr(acac)(3)/SiO2 exhibits the pattern of the molecular ion (m/z 100) in the range 400-600 K, which means the release of Hacac molecules, originating from Cr(acac)(3) molecules, H-bonded to surface hydroxyl groups. In contrast, the binding of Cr(acac)(3) molecules at the alumina surface is due to electron donor-acceptor interaction of acetylacetonate ligands with Al3+ sites. The TPD-MS of Cr(acac)(3)/Al2O3 exhibits mainly the fragment ion [H3CCO](+) (m/z 43) within the range 400-750 K, and only negligible intensity of the molecular ion (m/z 100) in the range 400-600 K.