| Popis: |
The infrared spectra of Fe 2 O 3 , ZnO, MoO 3 , and V 2 O 5 were investigated before and after the adsorption of ammonia at 20 °C and after its desorption at room and higher temperatures. A general feature of all the oxides was the presence on their surfaces of Lewis acid centers capable of adsorbing ammonia by the formation of a coordination bond. In addition, MoO 3 and V 2 O 5 adsorbed ammonia to yield NH 4 ions, indicating the presence of Bronsted centers on their surfaces which may be due to the hydrogen of OH groups. The ability of OH groups to release protons was assumed to be greatly affected by the electron-acceptor capacity of the cation of the oxide. The adsorption of ammonia on Fe 2 O 3 and ZnO is also accompanied by interaction with the surface oxygen to give surface amines or oxides of nitrogen. |
