ADSORPTION OF AMMONIA ON TIO2(001) AT ROOM-TEMPERATURE

The ammonia adsorption on the TiO2(001) surface has been studied using ultraviolet photoelectron spectroscopy (UPS), UV HeI lamp, 21.2 eV, and thermal desorption spectrometry (TDS). The layer at 300 K is formed by molecularly adsorbed ammonia, characterised by UPS structures at 11.8 and 7.4 eV. Electron damage of this initial layer as well as adsorption at a temperature of 340 K reveal that the surface species are NH2 and OH, the O being the lattice oxygen of TiO2. NH3 is the main desorbed product in thermal desorption experiments at T = 338 K, with first order kinetics and 80 kJ/mol desorption energy. Some ammonia is dissociated as NH2 and OH and after a slight temperature increase these products are completely dissociated as N and H, yielding by recombination N2 and H2 in the gas phase, their maximum desorption rates being at temperatures of 343 and 364 K, respectively.