Low Temperature Synthesis of NH3 from Atomic N and H at the Surfaces of FeS2{100} Crystals

Abstract

We have investigated the interaction of H2 and NH3 with {100} surfaces of iron pyrite (FeS2) in ultrahigh vacuum (UHV) and the synthesis of NH3 from the reaction of preadsorbed atomic N with atomic H, the H either preadsorbed on or arriving at the surface, all at surface temperatures of 170 K or above. Hydrogen adsorbs and reacts only when it arrives at the surface as atomic H, after cracking at a hot filament. Recombinative desorption of H2 occurs with a peak temperature of 225 K and is accompanied by desorption of H2S, formed by surface reaction of Hads with S, with a peak temperature of 260 K. NH3 adsorbs molecularly from the gas phase, albeit with some degree of partial dissociation, and desorbs with a peak temperature of 215 K. NH3 can be synthesized when the surface, after pre-exposure to activated nitrogen, is exposed to atomic H. The synthesized NH3 desorbs with a peak temperature of 230 K, demonstrating that all hydrogenation steps are feasible under these conditions; the process appears to be de...