Formation and hydrogenation of p(2×2)-N on Pt(111)

Interaction of HNCO with Au(111) surfaces

“…The most important findings are as follows: (i) NCO surface species developed in the catalytic reduction of NO is formed on the metals, but after its formation it migrates onto the supports, where it is stabilized [9][10][11][12][13]. This spillover process was first clearly demonstrated in the case of Rh/SiO 2 [12], (ii) the position of the absorption band of NCO species in the IR spectra varies with the nature of oxidic supports (Al 2 O 3 , MgO, TiO 2 , CeO 2 , ZSM-5) and fell in the range of 2210-2315 cm − 1 [7][8][9][10], (iii) as was revealed by the studies performed on metal single crystals in UHV, the characteristic vibration of NCO bonded to the metals is at 2170-2190 cm − 1 , which is almost independent of the nature of the metals [14][15][16][17][18][19][20][21][22][23][24][25][26], (iv) in contrast to the NCO attached to the oxides, isocyanate on the metals is a rather unstable species, and decomposes completely around 300-330 K [14][15][16][17][18][19][20][21][22][23][24][25][26]. Theoretical calculation using the density functional formalism (DFT) disclosed more details on the adsorbate-substrate interaction on different sites of metals and greatly contributed to the better understanding of the chemistry of NCO on catalyst surfaces [27][28][29]…”

Surface morphology of atomic nitrogen on Pt(111)

“…8 Electron-induced dissociation of ammonia is another approach but produces a mixture of NH, N, and H on the surface rather than a pure N layer. 9 A wellordered (2 × 2)-N overlayer on Pt(111) has been reported by Amorelli et al 10 where they utilized ammonia oxydehydrogenation by atomic oxygen (3O(ad) + 2NH 3 (ad) → 2N(ad) + 3H 2 O(g)) as a low energy pathway to form N. Later studies by Herceg et al 11 and Mudiyanselage et al 12 followed a similar method that involved annealing to 400 K a Pt(111) surface on which ammonia was coadsorbed with molecular oxygen at 85 K. They then studied the hydrogenation of the p(2 × 2)-N layer. Previous information on the surface morphology of the N layer was limited to low-energy electron diffraca) ykim@riken.jp b) mtrenary@uic.edu tion (LEED) results where two superstructures, (2 × 2) and ( √ 3 × √ 3)R30 • , were observed.…”

“…The reaction (ammonia oxydehydrogenation) used to form the N layer can produce other possible surface species such as NH 2 , NH, OH, and H 2 O. NH 2 is not a stable surface species and dissociates well below 300 K and H 2 O desorbs around 240 K according to a previous TPD measurement. 11 Moreover, the bright objects appear spherically symmetric and centered at hollow sites, but NH 2 and H 2 O should appear asymmetric. Both calculations 30 and experimental STM results 31 have shown that OH sits on top of a Pt atom with the OH bond almost parallel to the surface.…”

“…The assignment of N and O was based on comparison to the N-covered surfaces that will be discussed in Sec. III C. Moreover, the recombinative desorption of O 2 and N 2 occur at very different temperatures, [800 K for O(ad) + O(ad) → O 2 (g) 4 and 450 K for N(ad) + N(ad) → N 2 (g) 11 ]. Images obtained after annealing the mixed N+O surface to above 400 K contain only surface O atoms, which have an appearance that is similar to the less bright atoms shown in Fig.…”

“…Previous information on the surface morphology of the N layer was limited to low-energy electron diffraca) ykim@riken.jp b) mtrenary@uic.edu tion (LEED) results where two superstructures, (2 × 2) and ( √ 3 × √ 3)R30 • , were observed. 11 Scanning tunneling microscopy (STM) is a powerful tool for characterizing surface structures at the atomic level. Because a STM image is a view of the electronic structure rather than the actual topography of a surface, interpretation can be problematic.…”