Infrared Spectroscopic Study of the Carbon Dioxide Adsorption on the Surface of Ga2O3 Polymorphs

SEBASTIÁN E. COLLINS; MIGUEL A. BALTANÁS; ADRIAN L. BONIVARDI

Gramado, España

Simposio; XX Simpósio Ibero-americano de Catálise; 2006

The adsorption of CO2 over a set of gallium (III) oxide polymorphs with different crystallographic phases (a, b, and g) and surface areas was studied by in situ infrared spectroscopy. On the bare surface of the activated gallias [i.e., partially dehydroxylated under O2 and D2 (H2) at 723 K], several IR signals of the O-D (O-H) stretching mode were assigned to mono-, di- and tricoordinated OD (OH) groups bonded to gallium cations in tetrahedral and/or octahedral positions. After exposing the surface of the polymorphs to CO2 at 323 K, a variety of (bi)carbonate species emerged. The more basic hydroxyl groups were able to react with CO2, to yield two types of bicarbonate species: mono- (m-) and bidentate (b-). Together with the bicarbonate groups, IR bands assigned to carboxylate, bridge carbonate, bidentate carbonate, and polydentate carbonate species developed, up to approximately 600 Torr of CO2. However, only the bi- and polydentate carbonate groups still remained on the surface upon outgassing the samples at 323 K. Upon heating under flowing CO2 (760 Torr), most of the (bi)carbonate species vanished a T > 550 K, but polydentate groups remained on the surface up to 723 K.