N₂ Desorption in the Decomposition of Adsorbed N₂O on Rh(110)

Abstract

The decomposition of N 2 O(a) was studied on Rh(110) at 95-200 K through the analysis of the angular distributions of desorbing N 2 by means of angle-resolved thermal desorption. N 2 O(a) was highly decomposed during the heating procedures, emitting N 2 (g) and releasing O(a). N 2 desorption showed four peaks, at 105-110 K (β 4 -N 2 ), 120-130 K (β 3 -N 2 ), 140-150 K (β 2 -N 2 ), and 160-165 K (β 1 -N 2 ). The appearance of each peak was sensitive to annealing after oxygen adsorption and also to the amount of N 2 O exposure. The β 1 -N 2 peak was major at low N 2 O exposures and showed a cosine distribution. On the other hand, β 2 -N 2 and β 3 -N 2 on an oxygen-modified surface revealed inclined and sharp collimation at around 30°off the surface normal in the plane along the [001] direction, whereas β 4 -N 2 on a clean surface collimated at around 70°off the surface normal, close to the [001] direction. An inclined or surface-parallel form of adsorbed N 2 O was proposed as the precursor for inclined N 2 desorption.

Spatial and velocity distributions of desorbing products in steady-state NO+CO and N2O+CO reactions on Pd(110) and Rh(110)

“…15 N 2 O was introduced through a doser with a small orifice (diameter; 0.1 mm) while 13 CO and 15 NO were backfilled. The partial pressures of 13 C 16 O (P CO ) and 15 NO (P NO ) were kept constant by dosing the gases continuously.…”

“…No differences were found in the CO 2 distribution between them. The distribution in the NO+CO reaction was approximated as a {cos 13 (θ) + 0.2 cos(θ)} form at φ = 0 • and a {cos 4 (θ) + 0.2 cos(θ)} form at φ = 90…”

“…This point was observed when the N 2 O/CO pressure ratio was about 13. Both N 2 O and NO reductions are seriously retarded by the adsorbed oxygen [12][13][14], and the ratelimiting steps of the reactions (NO and N 2 O dissociation) are likely to proceed on clean parts that are free from oxygen, i.e., the inclined N 2 emission proceeds on the (1× 1) part.…”

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

“…17,53 The intermediate N 2 O is easily formed from the reaction N͑a͒ +NO͑a͒ in NO reduction on palladium, platinum, and rhodium surfaces. 12,[23][24][25] The reaction pathway through N 2 O decomposition is operative at low temperatures where NO͑a͒ is significant, more than N͑a͒.…”

The collimation angle shift of desorbing product N2 in a steady-state N2O+CO reaction on Rh(110)

“…36 This oxygen prevents N 2 O from dissociating because the local oxygen coverage is 0.5 ML. 42 The surface structure under reducing conditions is ͑1 ϫ 1͒, which is very active toward N 2 O dissociation. With the surface temperature decreasing below 540 K, the N 2 distribution on Rh͑110͒ narrows from a cos 9 ͑ ±62͒ form at 550 K to a cos 13 ͑ ±46͒ form at 450 K. This distribution is not as sharp as would be expected from the high translational temperature of approximately 3500 K. This is also in contrast to previous results, i.e., the product CO 2 in the active region of the CO oxidation on Rh͑110͒ …”