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A TPD study of nitric oxide decomposition on Pt(100), Pt(411) and Pt(211)
A34 44
Surface Science 209 (1989) 44-56 North-Holland, Amsterdam
A TPD ON
STUDY
OF
NITRIC
Pt(10O), Pt(411) AND
John
M. GOHNDRONE
OXIDE
DECOMPOSITION
Pt(211) and R.I. MASEL
*
Department of Chemical Engineering, University of Illinois, 1209 W. California Street, Box C-3 RAL, Urbana, IL 61801, USA Received 10 November 1988; accepted for publication 14 July 1988 Temperature programmed desorption (TPD) was used to compare nitric oxide dissociation on Pt(100), Pt(411) and Pt(211). These three faces were chosen for study because they possess sites with nearly the same orbital symmetries. However, the site densities are different on the three faces. It was found that all three faces show nearly identical reactivity for N O dissociation. Measured dissociation fractions were 66, 70 and 66% on the Pt(100), Pt(411) and Pt(211) surfaces respectively. N O dissociation on Pt(100) was inhibited by a (1 x 1) ---, (1 x 5) reconstruction, which creates a less active surface during the desorption process. However, the activation energy for N 2 formation was nearly identical (28 kcal/mol) on Pt(211) and Pt(411). Of course m a n y of the features of the TPD spectra varied from face to face. Pt(100) displays a complicated T P D spectrum, due to the presence of surface reconstructions during desorption process. The binding energy of NO on the (100) steps on Pt(211) was found to be unusually strong. However, examination of the data indicates that, except for some minor effects, the variations in reactivity with changing crystal face were as expected from an examination of the symmetries of the orbitals available for reaction, and do not scale with the site density.
Surface Science 209 (1989) 57-76 North-Holland, Amsterdam
57
LOW TEMPERATURE ADSORPTION AND CONDENSATION O F O z, H20 AND NO on Pt(lll), STUDIED BY CORE LEVEL AND VALENCE BAND
PHOTOEMISSION
W. RANKE
Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-IO00 Berlin 33, Germany Received 16 May 1988; accepted for publication 11 October 1988 The chemisorption and condensation of O z, H 2 0 and N O on P t ( l l l ) was studied between 20 and 90 K by photoelectron spectroscopy. All oxygen derived levels ( O l s , O2s and valence band) were measured using light energies of 1253.6, 120 and 21.2 eV. The rarely investigated O 2 s spectra turn out to be very useful for the analysis of different adsorbed species. Oxygen physisorbs and condenses at 20 K in neutral form. At 90 K, a strong O l s chemical shift (5.2 eV) is observed, the O 2 s level splitting into a bonding and antibonding state has almost vanished and the valence band completely changed, consistent with chemisorption of the ionic molecular species 0 2 - or O~- as proposed previously. The adsorption of this species is thermally activated. The valence band spectra of water in the submonolayer region and the thick ice layer differ considerably due to the strong hydrogen bonding in the condensed layer. Chemisorbed monomeric N O is observed in the submonolayer regime even at 20 K. Monomer chemisorption is not activated. The species chemisorbed at 20 K reduces the work function considerably ( - 4 2 0 meV for saturation at - 0.5 ML) consistent with predictions for terminal (on-top) N O ~+. Chemisorption at 80 K is m o n o meric, too. However, the O l s peak shape and the different work function change indicate a mixture of NO, probably on different sites. On top of the chemisorbed layer, N O condenses at 20 K in the form of (NO)2 dimers as concluded from the appearance of strong shake-up peaks in the O ls and the valence band spectra.
Surface Science 209 (1989) 44-56 North-Holland, Amsterdam
A TPD ON
STUDY
OF
NITRIC
Pt(10O), Pt(411) AND
John
M. GOHNDRONE
OXIDE
DECOMPOSITION
Pt(211) and R.I. MASEL
*
Department of Chemical Engineering, University of Illinois, 1209 W. California Street, Box C-3 RAL, Urbana, IL 61801, USA Received 10 November 1988; accepted for publication 14 July 1988 Temperature programmed desorption (TPD) was used to compare nitric oxide dissociation on Pt(100), Pt(411) and Pt(211). These three faces were chosen for study because they possess sites with nearly the same orbital symmetries. However, the site densities are different on the three faces. It was found that all three faces show nearly identical reactivity for N O dissociation. Measured dissociation fractions were 66, 70 and 66% on the Pt(100), Pt(411) and Pt(211) surfaces respectively. N O dissociation on Pt(100) was inhibited by a (1 x 1) ---, (1 x 5) reconstruction, which creates a less active surface during the desorption process. However, the activation energy for N 2 formation was nearly identical (28 kcal/mol) on Pt(211) and Pt(411). Of course m a n y of the features of the TPD spectra varied from face to face. Pt(100) displays a complicated T P D spectrum, due to the presence of surface reconstructions during desorption process. The binding energy of NO on the (100) steps on Pt(211) was found to be unusually strong. However, examination of the data indicates that, except for some minor effects, the variations in reactivity with changing crystal face were as expected from an examination of the symmetries of the orbitals available for reaction, and do not scale with the site density.
Surface Science 209 (1989) 57-76 North-Holland, Amsterdam
57
LOW TEMPERATURE ADSORPTION AND CONDENSATION O F O z, H20 AND NO on Pt(lll), STUDIED BY CORE LEVEL AND VALENCE BAND
PHOTOEMISSION
W. RANKE
Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-IO00 Berlin 33, Germany Received 16 May 1988; accepted for publication 11 October 1988 The chemisorption and condensation of O z, H 2 0 and N O on P t ( l l l ) was studied between 20 and 90 K by photoelectron spectroscopy. All oxygen derived levels ( O l s , O2s and valence band) were measured using light energies of 1253.6, 120 and 21.2 eV. The rarely investigated O 2 s spectra turn out to be very useful for the analysis of different adsorbed species. Oxygen physisorbs and condenses at 20 K in neutral form. At 90 K, a strong O l s chemical shift (5.2 eV) is observed, the O 2 s level splitting into a bonding and antibonding state has almost vanished and the valence band completely changed, consistent with chemisorption of the ionic molecular species 0 2 - or O~- as proposed previously. The adsorption of this species is thermally activated. The valence band spectra of water in the submonolayer region and the thick ice layer differ considerably due to the strong hydrogen bonding in the condensed layer. Chemisorbed monomeric N O is observed in the submonolayer regime even at 20 K. Monomer chemisorption is not activated. The species chemisorbed at 20 K reduces the work function considerably ( - 4 2 0 meV for saturation at - 0.5 ML) consistent with predictions for terminal (on-top) N O ~+. Chemisorption at 80 K is m o n o meric, too. However, the O l s peak shape and the different work function change indicate a mixture of NO, probably on different sites. On top of the chemisorbed layer, N O condenses at 20 K in the form of (NO)2 dimers as concluded from the appearance of strong shake-up peaks in the O ls and the valence band spectra.