INFRARED STUDY OF THE SURFACE-PROPERTIES OF METAL-OXIDES .2. INTERACTION OF AMMONIA WITH THE SURFACE OF FE2O3, ZNO, MOO3, AND V2O5

The infrared spectra of Fe2O3, ZnO, MoO3, and V2O5 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, MoO3 and V2O5 adsorbed ammonia to yield NH4 ions, indicating the presence of Brønsted 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 Fe2O3 and ZnO is also accompanied by interaction with the surface oxygen to give surface amines or oxides of nitrogen. © 1979.