Coadsorption of potassium and CO on Pt(111)

Кискинова, М.; Pirug, G.; Bonzel, H.P.

doi:10.1016/0039-6028(83)90005-5

Cited by 221 publications

(78 citation statements)

References 44 publications

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“…1 shows the calculated surface dipole, m s m͑Pt 25 K͒ 2 m͑Pt 25 ͒, as a function of z K for the hollow site. At equilibrium we find m s 7.8 debye (in good agreement with the initial dipole deduced from work function measurements [16]). The dynamical dipole of the vibration is given by dm s ͞dz K 1.1 electrons (to be compared with the value of 1.0 electrons derived from the measured EELS intensity).…”

Section: Incorporation Of Potassium At the Pt(111) Surfacesupporting

confidence: 87%

Incorporation of Potassium at the Pt(111) Surface

et al. 1997

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Using electron-energy-loss spectroscopy and scanning tunneling microscopy, we find that at room temperature the binding site of K at the Pt(111) surface changes with increasing coverage. At low coverages, K adsorbs at surface hollow sites, forming an ionic bond with the substrate. Above a coverage of 0.1 monolayers, we observe a slow migration of K to subsurface binding sites in the second Pt layer. The measured vibrational frequencies are in quantitative agreement with cluster calculations for the proposed surface and subsurface bonding geometries. [S0031-9007(97) PACS numbers: 71.15.Fv, 71.20.Be, 71.20.Dg, 82.65.My For many years, the interaction of alkali metal (AM) atoms with surfaces was discussed in terms of the chargetransfer model introduced by Gurney [1], which implicitly assumes that the AM atoms adsorb without inducing any morphological changes in the surface. According to this model, the surface bond is due to the partial transfer of the AM s electron to the substrate, which gives rise to a surface dipole and to an AM-AM repulsion that prevents the formation of islands. This picture is the cornerstone of our present understanding of the role of AM as promoters of catalytic reactions, as well as of the mechanism by which the work function is lowered following AM adsorption [2]. However, new results on the adsorption geometry of AM atoms at metal surfaces are beginning to modify this classical picture. Experimental and theoretical investigations have shown that, in the medium-and high-coverage regime, 2D condensation [3] and surface alloy formation [4,5] are favorable under certain circumstances. For low coverages, Lehmann et al. have proposed that K becomes incorporated into the Pt(111) surface directly upon adsorption [6]. In this Letter, we also report a subsurface configuration for K adsorbed at the Pt(111) surface, but in contrast to the results of Lehmann et al., we show that the subsurface state becomes energetically favorable only for coverages above 0.1 monolayers (ML) [7], and that the conversion to the subsurface site is activated. For coverages below 0.1 ML, we find that K adsorbs at hollow sites of the surface, with an ionic bond in which one-half of the K 4s electron is transferred to the substrate. Our characterization of the K͞Pt(111) system was carried out using electronenergy-loss spectroscopy (EELS), scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and electronic structure calculations using the cluster method.The experiments were performed using two Pt(111) crystals, both of which were cut and polished to an accuracy of 0.1 ± . Well-ordered surfaces were prepared via sputtering with Ne 1 ions, followed by annealing to 1250 K. Residual C contamination was removed by exposing the surface to O 2 at 950 K, followed by subsequent annealing to 1250 K to remove the surface oxide layer. K was evaporated onto the surface with a commercial getter source, and the coverage of the adsorbed K was determined using AES and low-energy electron diffraction. The evaporation ...

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Section: Incorporation Of Potassium At the Pt(111) Surfacesupporting

confidence: 87%

Incorporation of Potassium at the Pt(111) Surface

et al. 1997

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“…A related system of CO adsorbed on a Pt/K surface has been studied by Kiskinova et al [5]. The results are similar to CO 2 in that the addition of the alkali metal lowers the work function, and increases electron transfer to the CO molecule.…”

Section: Introductionmentioning

confidence: 62%

“…While there are no experimental data specific to the dilute limit of a single potassium adatom on a surface of 37 Pt atoms corresponding to our model, the experimental data show a decrease in work function with increasing K coverage, with a minimum work function of 1.3 eV at h K = 0.17 [5]. In our model, the calculated clean Pt work function (E ionized Pt(111) -E Pt(111) ) is 5.6 eV and compares to the experimental value of 5.7 eV [20].…”

Section: K Adatommentioning

confidence: 78%

“…Modification of the surface chemistry of ground state processes involving adsorbates on metals by the addition of alkali metal atoms to the surface has been the subject of many experimental and theoretical investigations [1][2][3][4][5][6]. When alkali metal atoms are adsorbed, electron donation to the bulk metal is accompanied by a decrease in work function of the system.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical treatment of excited electronic states of adsorbates on metals: Electron attachment to CO2 adsorbed on K-modified Pt(111)

Sremaniak¹,

Whitten²

2008

Surface Science

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“…In the particular case of CO adsorption on platinum single-crystal surfaces, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] the presence of metallic potassium (or cesium) (1) strengthens the Pt-CO bond, (2) weakens the C-O bond, increasing the probability for CO dissociation, and (3) promotes the adsorption of CO into bridgebonded platinum sites.…”

Section: Introductionmentioning

confidence: 99%

Microcalorimetric and Reaction Kinetic Studies of Alkali Metals on Pt Powder and Pt/SiO₂and Pt/Sn/SiO₂Catalysts

1996

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Microcalorimetric measurements of CO adsorption at 403 K on reduced Pt powder gave an initial heat of 140 kJ/mol and a saturation CO coverage of 30 µmol/g Pt. The addition of metallic Rb and Cs to Pt increased the initial heats of CO adsorption by 20 and 40 kJ/mol and extended the CO adsorption capacity to 110 and 60 µmol/g Pt, respectively. The increase in CO adsorption capacity is caused by formation of an alkali-CO complex at 403 K, with an interaction heat near 120 kJ/mol. Microcalorimetric measurements of CO adsorption at 403 K on Pt/SiO 2 (0.85 wt % Pt) and Pt/Sn/SiO 2 (2.61 wt % Pt) catalysts showed initial heats of 140 and 130 kJ/mol and saturation CO coverages of 25 and 65 µmol/g, respectively. The addition of K, Rb, and Cs salts (1:5 atomic Pt/alkali) to Pt/SiO 2 followed by treatment in H 2 at 773 K did not alter the properties of these materials for CO adsorption at 403 K or for reactions with isobutane at 673 K. In contrast, the addition of Na and Cs salts (1:3 atomic Pt/alkali) to Pt/Sn/SiO 2 significantly decreased the CO saturation coverage, did not affect the initial heat of CO adsorption, and increased the selectivity for isobutane dehydrogenation. These results indicate that while the alkali species are not present in the metallic state on Pt/Sn/SiO 2 catalysts, these alkali species are probably associated with Sn on Pt/Sn particles, thereby inhibiting isomerization, hydrogenolysis, and coking reactions by decreasing the size of surface platinum ensembles.

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Coadsorption of potassium and CO on Pt(111)

Cited by 221 publications

References 44 publications

Incorporation of Potassium at the Pt(111) Surface

Incorporation of Potassium at the Pt(111) Surface

Theoretical treatment of excited electronic states of adsorbates on metals: Electron attachment to CO2 adsorbed on K-modified Pt(111)

Microcalorimetric and Reaction Kinetic Studies of Alkali Metals on Pt Powder and Pt/SiO₂and Pt/Sn/SiO₂Catalysts

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Coadsorption of potassium and CO on Pt(111)

Cited by 221 publications

References 44 publications

Incorporation of Potassium at the Pt(111) Surface

Incorporation of Potassium at the Pt(111) Surface

Theoretical treatment of excited electronic states of adsorbates on metals: Electron attachment to CO2 adsorbed on K-modified Pt(111)

Microcalorimetric and Reaction Kinetic Studies of Alkali Metals on Pt Powder and Pt/SiO2and Pt/Sn/SiO2Catalysts

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Microcalorimetric and Reaction Kinetic Studies of Alkali Metals on Pt Powder and Pt/SiO₂and Pt/Sn/SiO₂Catalysts