Interactions of N2 molecules adsorbed on smooth and roughened Ni(111) surfaces

Quick, Anthony; Browne, V.M.; Fox, S.G.; Hollins, P.

doi:10.1016/0039-6028(89)90565-7

Cited by 24 publications

(7 citation statements)

References 21 publications

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“…A very faint p(2X2) LEED pattern was observed, but the coverage ofN(a) was not determined. The important findings were that on all modified Ni(111) surfaces, N2 stretching bands were observed at higher wave numbers, and that these modifiers decreased the saturation IR in:tensitydue to chemisorbed N 2 • In addition, a roughened Ni ( 111) (111) The experimental results obtained in this investigation are somewhat different from an earlier LEED/lRAS study 8 and these differences are listed in Table I. Based on the reported thermal stability of the N2 adlayer at 120 K in vacuum, 8 compared to our measurements where all chemisorbed N2 would have desorbed, it would seem that the chemisorbed N z species in Ref.…”

Section: B Iras Measurements Of Chemisorbed N2 Speciescontrasting

confidence: 88%

“…Low-energy electron diffraction (LEED) was used in complementary measurements to get information about the long-range order of the admolecules. We have found entirely different results for N2 adsorption on Ni( 111) compared to Quick et al,8 and a comparison of these differences will be discussed below.…”

Section: Introductionmentioning

confidence: 50%

“…Since this chemical shift even affects the bands at low coverage, it is most likely due to a long-range interaction. 8 ,10…”

Section: N2 -mentioning

confidence: 99%

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N2 chemisorption on Ni(111). An infrared investigation under steady-state conditions

Yoshinobu

Zenobi

et al. 1991

The Journal of Chemical Physics

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The adsorption ofN 2 on Ni( 111) at 89-115 K under steady-state (quasiequilibrium) conditions has been studied using Fourier-transform infrared reflection absorption spectroscopy (FT-lRAS) and low-energy electron diffraction (LEED). At very low coverage, a single N==N absorption band is observed at 2218 cm -I which is assigned to a singleton N2 adspecies. With increasing N z pressure, two other bands develop at 2212-2208 and 2204-2203 cm -I, and a faint (v1xyj)R 30· LEED pattern is observed. At even higher pressure, a sharp (YJxV3)R 30· LElED pattern develops together with a relatively broad single band at 2194 cm-I • The enthalpy of adsorption ofN2 on Ni(111) is estimated to be -8.4 kcaVmol at zero coverage from isothermal IRAS measurements. Slight attractive interactions between N2 adspecies are detected. The origins of the vibrational features which are related to island formation will be discussed in detail.J. Chern. Phys. 95 (12). 15

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Section: B Iras Measurements Of Chemisorbed N2 Speciescontrasting

confidence: 88%

Section: Introductionmentioning

confidence: 50%

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N2 chemisorption on Ni(111). An infrared investigation under steady-state conditions

Yoshinobu

Zenobi

et al. 1991

The Journal of Chemical Physics

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“…For quantification of B 5 sites, van Hardeveld and van Montfoort introduced the method of using IR measurements on chemisorbed N 2 , and later single-crystal studies , have supported that the observed IR bands from this method do arise from steps/defects such as the B 5 sites. We conducted IR measurements of N 2 adsorbed on the prereduced Rh/SiO 2 samples at 25 °C, which resulted in a single IR band at 2250 cm –1 (see Figure S5).…”

Section: Resultsmentioning

confidence: 99%

Rationalizing an Unexpected Structure Sensitivity in Heterogeneous Catalysis—CO Hydrogenation over Rh as a Case Study

et al. 2021

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A common expectation in heterogeneous catalysis is that the optimal activity will occur for the particle size with the highest concentration of undercoordinated step, edge, or corner sites, expectedly in the <5 nm range. However, many metal-catalyzed reactions follow a different trend, where the turnover frequency (TOF, here rate per surface atom) is instead lower for these smaller particles and increases strongly with increasing size toward a stabilized level with a size-independent TOF. Here, we use one of these reactions, the Rh-catalyzed CO hydrogenation to hydrocarbons and C2-oxygenates, to illuminate the origin of this effect. Studying Rh/SiO2 catalysts, we show that smaller (<4 nm) Rh particles are richer in undercoordinated edge, corner, and step sites, but are nevertheless of lower activity because the entire surface, including the planar facets, is shifted to a prohibitively high adsorbate coveragein this case of CO. In transient experiments, where the inhibiting adsorbates are allowed to desorb, smaller 1.7 nm Rh particles and larger 3.7 nm Rh particles reach similar rates of CO activation despite the steady-state TOF being an order of magnitude higher on the larger particles. This shows that it is a prohibitive adsorbate coverage under reaction conditions rather than a lower number of active sites or a lower intrinsic activity of the sites that causes the lower activity of the smaller particles. In steady-state experiments at 20 bar, the TOF for CO hydrogenation increases by 55% from 3.7 nm Rh particles to 5.3 nm Rh particles even though the measured concentration of step sites decreases by 30% in this size range. This indicates that such undercoordinated sites are not necessarily the primary active centers and that the reaction is instead focused on the planar facets. The reaction kinetics show that the reaction becomes increasingly pressure-dependent with increasing particle size, implying that the surface becomes increasingly free of adsorbates on larger particles. Taken together with the indications that the reaction may be focused on the planar facets, this leads to the new insight that it is a prohibitively high adsorbate coverage on the entire surface (and not just on a minority of undercoordinated sites) that is the primary reason for the low activity of small nanoparticles. The identification of a detrimental high-coverage state for small particles is expected to be of general relevance to the many industrially important reactions sharing the same behavior. The high-coverage state is not exclusively negative, but can also facilitate different reaction pathways. It is the higher CO coverage on small particles that drives the C2-oxygenate formation and is the reason for the high selectivity of rhodium to such complex products, which is at its highest for the smallest (∼2 nm) investigated particles.

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“…9 They found that ͑i͒ the chemisorbed species only appears below 70 K where the N 2 molecules stand up on the surface, ͑ii͒ at sufficiently low temperature ͑e.g., 20 K͒ the chemisorbed and physisorbed states grow simultaneously leading to the formation of a monolayer, and ͑iii͒ the N 2 molecules in the multilayers are regarded as physisorbed and condensed species. LEED measurements have been carried out also, but the conclusions seem controversial; Quick et al observed a p(2ϫ2) pattern after 1 L (1 Lϭ1ϫ10 Ϫ6 Torr s) exposure at 83 K, 10 while Yoshinobu et al reported a ()ϫ))R30°structure under steady-state conditions at 89 K. 11 Höfer et al measured vibration-resolved photoemission spectra of N 2 physisorbed on Ni͑111͒ and indicated that the line shape of the 1 u -derived band is reproduced well using a hopping model, where a photohole in the ionized molecule transfers to neighbors. 12 In contrast to the case of Ni͑111͒, the coexistence of the chemisorbed and physisorbed species has not been observed in the case of Ni͑100͒ or Ni͑110͒ in the submonolayer region.…”

Section: Introductionmentioning

confidence: 99%

Local electronic states in the topmost surface layer probed by metastable atom electron spectroscopy: N2adsorbed and condensed onNi(111
Suzuki
¹
,
Taoka
²
,
Aoki
³

et al. 2001
Phys. Rev. B
5
0
4
0
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Electron emission spectra obtained by thermal collisions of He*(2 3 S) metastable atoms with N 2 molecules on a Ni͑111͒ surface in the chemisorbed, physisorbed, and condensed phases were measured together with the gas-phase spectrum. In the gas-phase collision where the metastable atoms approach randomly oriented N 2 molecules, Penning ionization rates for the 3 g and 2 u states are almost identical reflecting their spatial extent, while that for the 1 u state is rather small. In the saturated overlayer at ϳ50 K where the N 2 molecules are chemisorbed with the molecular axes perpendicular to the surface, the 3 g -derived state is drastically enhanced relative to the 2 u -derived state. This indicates that, upon chemisorption, two states are strongly modified in space by mixing with each other to yield a strong charge localization, i.e., an outer N atom in the 3 g -derived state gains considerable charge whereas an outer N atom in the 2 u -derived state loses it. The orbital mixing was confirmed by crystal orbital overlap population obtained using density functional theory within a generalized gradient approximation. Our spectra at ϳ20 K show that the physisorbed N 2 molecules are located on the chemisorbed species with a parallel orientation in the monolayer region and then condense to form a multilayer. We also found a characteristic band shift and narrowing with increasing layer thickness and these findings are discussed in terms of two final-state relaxation effects.

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Interactions of N2 molecules adsorbed on smooth and roughened Ni(111) surfaces

Cited by 24 publications

References 21 publications

N2 chemisorption on Ni(111). An infrared investigation under steady-state conditions

N2 chemisorption on Ni(111). An infrared investigation under steady-state conditions

Rationalizing an Unexpected Structure Sensitivity in Heterogeneous Catalysis—CO Hydrogenation over Rh as a Case Study

Local electronic states in the topmost surface layer probed by metastable atom electron spectroscopy: N2adsorbed and condensed onNi(111
Suzuki
¹
,
Taoka
²
,
Aoki
³

et al. 2001
Phys. Rev. B
5
0
4
0
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Interactions of N2 molecules adsorbed on smooth and roughened Ni(111) surfaces

Cited by 24 publications

References 21 publications

N2 chemisorption on Ni(111). An infrared investigation under steady-state conditions

N2 chemisorption on Ni(111). An infrared investigation under steady-state conditions

Rationalizing an Unexpected Structure Sensitivity in Heterogeneous Catalysis—CO Hydrogenation over Rh as a Case Study

Local electronic states in the topmost surface layer probed by metastable atom electron spectroscopy: N2adsorbed and condensed onNi(111Suzuki1, Taoka2, Aoki3 et al. 2001Phys. Rev. B5040View full textAdd to dashboardCite

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Local electronic states in the topmost surface layer probed by metastable atom electron spectroscopy: N2adsorbed and condensed onNi(111
Suzuki
¹
,
Taoka
²
,
Aoki
³

et al. 2001
Phys. Rev. B
5
0
4
0
View full text Add to dashboard Cite