Coadsorption of cyanogen and potassium on Pt(111)

doi:10.1016/0039-6028(87)90188-9

Surface Science

Volume 181, Issue 3, 2 March 1987, Pages L156-L162

https://doi.org/10.1016/0039-6028(87)90188-9 Get rights and content

Abstract

The coadsorption of potassium and cyanogen on Pt(111) has been studied by thermal desorption spectroscopy. A new feature in the cyanogen desorption is identified at 363 K, 30 K above the desorption temperature for the molecular state of cyanogen on clean Pt(111). The potassium/cyanogen interaction which leads to the new desorption feature has a reasonably well defined 1 : 1 stoichiometry.

References (29)

G. Brodén et al.
Chem. Phys. Letters
(1980)
E.L. Garfunkel et al.
Surface Sci.
(1982)
G. Pirug et al.
Surface Sci.
(1982)
H.P. Bonzel et al.
Chem. Phys. Letters
(1985)
M.P. Kiskinova et al.
Surface Sci.
(1985)
J.C. Bertolini et al.
Surface Sci.
(1985)
J.E. Crowell et al.
Surface Sci.
(1982)
M.P. Kiskinova et al.
Surface Sci.
(1983)
M.P. Kiskinova et al.
Surface Sci.
(1984)
Y.-M. Sun et al.
Surface Sci.
(1984)

H.S. Luftman et al.

Surface Sci.

(1984)

H.S. Luftman et al.

Surface Sci.

(1984)

D.R. Mullins et al.

Surface Sci.

(1985)

H.S. Luftman et al.

Surface Sci.

(1984)

Cited by (8)

Vibrational spectroscopy and theory of alkali metal adsorption and co-adsorption on single-crystal surfaces
2013, Surface Science Reports
Citation Excerpt :
Hence, systematic studies of co-adsorption systems are essential for a more complete understanding of heterogeneous catalysis. Co-adsorption studies of lithium [116,195–200], sodium [201–212], potassium [46,57,149,213–246], cesium [149,228,247–262] and rubidium [263–266] with simple molecules (CO, CO2, H2O, NO etc.) have been carried out in order to shed the light on the AM promotion effect on surface chemical reactivity. A microscopic understanding of these and related phenomena is important because of their impact on processes such as vibrational excitations, surface scattering, photochemical reactions and charge and energy transport on surfaces.
Alkali-metal (AM) atoms adsorbed on single-crystal surfaces are a model system for understanding the properties of adsorption. AM adsorption, besides introducing new overlayer vibrational states, induces significant modifications in the surface vibrational structure of the metal substrate. Several studies of the vibrational properties of AM on metal surfaces have been carried out in last decades. Most of these investigations have been performed for low coverages of AM in order to make the lateral interaction among co-adsorbates negligible. The adsorbed phase is characterized by a stretch (S) vibrational mode, with a polarization normal to the surface, and by other two modes polarized in the surface plane, known as frustrated translation (T) modes. The frequencies and intensities of these modes depend on the coverage, thus providing a spectroscopic signature for the characterization of the adsorbed phases.
The vibrational spectroscopy joined to an ab-initio theoretical analysis can provide useful information about surface charge re-distribution and the nature of the adatom–surface bond, establishing, e.g., its partial ionicity and polarization. Gaining this information implies a significant advancement in our knowledge on surface chemical bonds and on catalytic reactions occurring in AM co-adsorption with other chemical species. Hence, systematic studies of co-adsorption systems are essential for a more complete understanding of heterogeneous catalysis.
The two principal experimental techniques for studying the vibrations of AM adsorbed phases are high-resolution electron energy loss spectroscopy (HREELS) and inelastic helium atom scattering (HAS), the former being better suited to the analysis of the higher part of the vibrational spectrum, while the latter exploits its better resolution in the study of slower dynamics, e.g., T modes, surface acoustic phonons and diffusive phenomena. Concerning AM co-adsorption systems, reflection–absorption infrared spectroscopy (RAIRS) has been also used (as well as HREELS) for obtaining information on the influence of AM adsorption on the vibrational properties of co-adsorbates.
In this review an extended survey is presented over:
- a)
  the existing HREELS and HAS vibrational spectroscopic studies for AM adsorbed on single-crystal metal surfaces;
- b)
  the theoretical studies based on semi-empirical and ab-initio methods of vibrational structure of AM atoms on metal surfaces;
- c)
  the vibrational (HREELS, RAIRS, TRSHG) characterization of the co-adsorption on metal surfaces of AM atoms with reactive species.
A detailed microkinetic model for diesel engine emissions oxidation on platinum based diesel oxidation catalysts (DOC)
2012, Applied Catalysis B: Environmental
In this work, a comprehensive 124-step (62 reversible) microkinetic model is developed for the oxidation of five major diesel engine emission components (carbon monoxide, nitric oxide, formaldehyde, ammonia, and hydrogen cyanide) on Pt. Kinetic parameters for the detailed microkinetic model are extracted from ultra-high vacuum (UHV) temperature programmed desorption/reaction (TPD/TPR) experiments in literature. Starting with these kinetic parameters as initial estimates, the surface reaction mechanism is extensively tested against practically more relevant operating conditions, such as atmospheric pressure, dilute emissions concentrations, and short residence times, typically experienced by the Diesel Oxidation Catalysts (DOCs). In each of the five oxidation cases, mechanistic analysis is presented to uncover the most important reaction chemistry. The microkinetic model shows very good agreement with multiple experimental data sets on monolith and fixed bed reactor scale, for the oxidation of all five components. For practical implementation, the mechanism is further reduced to 94 steps (47 reversible) using preliminary model reduction.
Effects of a potassium adlayer on the interaction of nitrogen with the Rh(111) surface
1991, Surface Science
The adsorption of N₂ and atomic nitrogen generated in a high-frequency discharge tube (N + N₂) has been studied on clean and K-covered Rh(111) surfaces with TDS, AES, and work-function meaurements at 100–600 K. Dinitrogen adsorbed on a clean Rh at 100 K desorbs with T_p=155–160 K. No adsorption and dissociation of N₂ was experienced at 300–600 K under UHV condition. Preadsorbed K suppresses the uptake of N₂ at 100 K. TDS and AES experiments did not show the formation of any new nitrogen adsorption state. A very limited dissociation of N₂, induced by potassium adlayer, was observed only at 500 K and at high N₂ pressure. The atomic nitrogen bonds strongly to the Rh(111) surface and desorbs associatively in two stages at T_p=561–712 K and T_p=453 K. The preadsorbed K influenced only little the rate and extent of the uptake of nitrogen atom and slightly lowered the peak temperatures for the associative desorption of nitrogen in the main state. At the same time, potassium adatoms induced the formation of a new, high-temperature state with T_p=720–800 K. A significant stabilization of potassium (around monolayer) was found in the coadsorbed layer. A fraction of potassium desorbed together with the more stable nitrogen. This feature indicates a direct interaction and a mutual stabilization between adsorbed K and N.
Photoelectron spectroscopy studies of the hydrogenation of cyanogen on Pt(111): Comparison with HCN and ethylenediamine
1989, Surface Science
X-ray photoelectron spectra as a function of anneal temperature are used to compare the thermally initiated chemistry of C₂N₂ + H₂ on Pt(111) with that of C₂N₂, HCN and ethylenediamine. These spectra show that the product of the reaction of C₂N₂ with coadsorbed hydrogen (the γ state of C₂N₂ + H₂/Pt(111)) is not HCN but is more likely to be a surface di-imine species. The N1s binding energy of this partially hydrogenated species is ∼ 399.3 eV. HCN adsorption on Pt(111) leads to two distinct chemical species with N1s binding energies of 398.6 and 396.9 eV which are interpreted in terms of molecular and dissociative adsorption respectively.
Adsorption and dissociation of HCN on the Pt(111) and Pt(112) surfaces
1988, Surface Science
The interaction of HCN with the Pt(111) and Pt(112) surfaces has been studied with temperature programmed desorption (TPD), scanning kinetic spectroscopy (SKS), LEED and work function measurements (Δφ) in the temperature range 87 to 1000 K. The only desorption products observed were H₂, C₂N₂ (cyanogen) and HCN. Labelling studies utilizing D¹³CN + HCN revealed that HCN desorbs molecularly in three different low temperature states, while higher temperature β states were due to recombination of H(a) + (CN)(a). Different β-state desorption behavior was observed on Pt(112) which may be due to competitive desorption effects. Evidence suggests that the highest temperature molecular desorption state of HCN may act as a precursor to dissociation. The high step density Pt(112) surface was found to be more effective in promoting dissociation of HCN. The following sequence of LEED patterns was observed on Pt(111) with decreasing coverage of HCN beginning with monolayer coverage: (3×3) → c(4×2) → (2×2) → (1×1). Both HCN(a) and CN(a) were found to give an overall work function decrease on Pt(111) yielding values of −1.2 and −0.8 V, respectively at saturation. LEED measurements in conjunction with TPD and Δφ results suggest that HCN is bonded in a linear fashion at saturation with the nitrogen bonded to Pt. After dissociation, CN(a) is likely bonded with the molecular axis parallel to the Pt surface.
Activation barriers for chemisorption of deuterium on aluminum cluster ions: Influence of oxygen preadsorption
1988, Chemical Physics Letters
Activation barriers for chemisorption of deuterium on size-selected aluminum clusters with one or two preadsorbed oxygen atoms (Al_nO_k⁺, n=10–27, k=1, 2) are reported. These measurements were made by determining the collision energy threshold for chemisorption using low energy ion beam techniques. Oxygen preadsorption has a dramatic effect on the activation barriers for some of the smaller clusters (n<18). For example, preadsorption of one oxygen atom on Al₁₅⁺ causes the activation barrier to increase by over 0.5 eV from that observed with the bare cluster. The origin of these very size-specific changes caused by oxygen preadsorption may be the result of a global perturbation of the cluster's electronic properties rather than involving a site-specific mechanism.

View all citing articles on Scopus

View full text

Surface science lettersCoadsorption of cyanogen and potassium on Pt(111)

Abstract

Chem. Phys. Letters

Surface Sci.

Surface Sci.

Chem. Phys. Letters

Surface Sci.

Surface Sci.

Surface Sci.

Surface Sci.

Surface Sci.

Surface Sci.

Surface Sci.

Surface Sci.

Surface Sci.

Surface Sci.

Surface science letters
Coadsorption of cyanogen and potassium on Pt(111)