Formation of NH3 and N2 from atomic nitrogen and hydrogen on rhodium (111)

Abstract

Reactions of adsorbed N atoms on Rh͑111͒ to N 2 and NH 3 were studied with temperature programmed desorption, temperature programmed reaction spectroscopy, and static secondary ion mass spectrometry. For N-atom coverages below Ϸ0.15 monolayers, desorption of N 2 follows simple second-order kinetics, but at higher coverages the desorption traces broaden to higher temperatures. Hydrogenation to NH 3 can be described by a stepwise addition of H atoms to N ads in which the reaction from NH 2,ads ϩH ads to NH 3 ,ads determines the rate. The activation energy for the rate determining step is 76 kJ/mol. The desorption of NH 3 from Rh͑111͒ was studied separately. The kinetic parameters for desorption at low NH 3 coverage are 81 kJ/mol and 10 13 s Ϫ1, but the rate of desorption increases rapidly with increasing NH 3 coverage. It is argued that the remarkable coverage dependence of the desorption rate is unlikely to be caused by lateral repulsive interactions but may be due to a coverage dependence of the pre-exponential factor.

Static secondary ion mass spectrometry (S-SIMS) Part 2: material science applications

“…The use of (TP) S-SIMS is also applicable to more complex systems, e.g., reactions of NO with C 2 H 4 co-adsorbed on Rh(111) and with CO on Rh(110) surfaces (van Hardeveld et al, 1996;1997a;Schmatloch et al, 1995). The preparation of atomic nitrogen layers on Rh(111) monolayers by adsorption of NO and selective removal of the atomic oxygen by reaction with H 2 , could be followed by monitoring the Rh 2 N , Rh 2 O and Rh 2 NO signals (van Hardeveld et al, 1997b;1997c). Their further conversion into N 2 and NH 3 was also studied and the detected ions allowed identi®cation of N and NH 2 as predominant reaction intermediates, while also small amounts of NH 3 were detected.…”

Ammonia Adsorption and Decomposition on Co(0001) in Relation to Fischer–Tropsch Synthesis

“…It is a reactant in the Pt-catalyzed reaction of ammonia with methane in HCN synthesis 1 and in the oxidation of NH 3 during nitric acid production (Ostwald process) 2 where a Pt−Rh gauze is used as the catalyst. The interaction of NH 3 with various metal surfaces such as Fe, 3 Pt, 4−6 Ir, 7 Ru, 8−10 Ag, 11 Cu, 12 Ni, 13,14 and Rh 15,16 has been reported in the literature. Some other fundamental studies have focused on ammonia oxidation, where ammonia takes part as the reactant.…”

Detailed study of the plasma-activated catalytic generation of ammonia in N2-H2 plasmas

“…The above picture is in agreement with the general proposed reaction mechanism for the ammonia production at the surface in N 2 -H 2 plasmas, [16][17][18] but also in surface studies related to catalysis. 6,7,[52][53][54] In conclusion, ammonia is mainly produced by association of atomic and molecular radicals at the surface, e.g., by the successive hydrogenation of adsorbed nitrogen atoms and the intermediates NH and NH 2 at the surface of the plasma reactor.…”