A New Approach to Loss of Alkali Promoter from Industrial Catalysts: Importance of Excited States of Alkali

Holmlid, Leif; Engvall, Klas; Åman, Carina; Menon, P.G.

doi:10.1016/s0167-2991(08)64057-4

Cited by 14 publications

(11 citation statements)

References 9 publications

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“…Strong interaction between the flux from the beam and the thermally desorbing flux from the surface is also reported, such that peaks observed without an impinging atom beam are removed by the beam flux. These observations are related to the existence of excited clusters K* identified in previous studies [1][2][3][4]10]. The results demonstrate the importance of scattering studies to investigate the nature of the excited species at catalyst surfaces.…”

Section: Introductionsupporting

confidence: 78%

“…At low sample temperatures and large surface densities of K, a dominant peak in the normal direction can sometimes also be found at low sample temperatures, which is due to cluster formation just outside the surface. This point was treated further in [1].…”

Section: Desorption From the Catalyst Surfacementioning

confidence: 97%

“…In the experiments in [1][2][3] the thermally desorbing atoms are observed by surface ionization detection. In Sect.…”

Section: Desorption From the Catalyst Surfacementioning

confidence: 99%

“…It is thus reasonable to conclude that the special angular distributions for desorption are due to the special properties of Rydberg states at surfaces, even if a direct coupling to the long-range potential is difficult to prove at this stage. One special property is the facile formation of clusters due to the very large polarizabilities of Rydberg species, and the large normal peaks found in some cases are due to formation of clusters just outside the surface [1,10,20].…”

Section: Desorption From the Catalyst Surfacementioning

confidence: 99%

“…Angular distributions of desorbing potassium neutrals and ions from special surfaces have been shown [1][2][3][4] to depart strongly from the expected equilibrium cosine-type distributions. A surface scattering behavior of potassium atom beams has also recently been observed [2,3] from the same kind of surfaces.…”

Section: Introductionmentioning

confidence: 99%

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Scattering of a potassium atom beam from potassium promoted catalyst surfaces via electronically excited clusters

Holmlid

1995

Z Phys D - Atoms, Molecules and Clusters

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Abstract. Surface scattering of potassium atom beams is observed from surfaces of a potassium promoted catalyst, which is known to emit Rydberg K* species and clusters K*. The surfaces studied are cut flat from pellets of an industrial catalyst, the promoted iron oxide catalyst for styrene production. The scattering is studied in the temperature range 500-1000 K in an UHV apparatus with a K atom beam at 45 ° towards the normal, with surface ionization and ion detection over an angular range of -90 ° to + 90 ° with respect to the surface normal. Bilobular scattering patterns are observed, which are mainly back-scattering at low temperatures, below 750 K. A large signal due to ions emitted in the backwards direction is also found with a voltage on the sample. This back-scattering indicates that the scatterers are heavy clusters outside the surface. The ion formation in the backwards direction is proposed to be due to collisions with electronically excited clusters K* of the type recently observed by field ionization detection (Kotarba et al. 1994). The bilobular scattering transforms into asymmetric patterns with a larger forward (specular) lobe at higher temperatures, above 800 K. Only a small fraction of the beam molecules is scattered off the surface. The scattering is well described by inelastic surface scattering theory. This shows that the actual scattering surface is rather flat, which is proposed to be due to an antibondii~g Rydberg type interaction, of long range (hundreds of A), between the impinging excited K atom and the surface. The temperature dependence of the neutral scattering gives a barrier of 0.96 eV, close to what is generally found for Rydberg species emission from such surfaces. At larger K s~r-face densities, the contributions to the peaks from the beam flux is shown to agree with this picture involving collisions with excited clusters outside the surface.

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Section: Introductionsupporting

confidence: 78%

Section: Desorption From the Catalyst Surfacementioning

confidence: 97%

“…In the experiments in [1][2][3] the thermally desorbing atoms are observed by surface ionization detection. In Sect.…”

Section: Desorption From the Catalyst Surfacementioning

confidence: 99%

Section: Desorption From the Catalyst Surfacementioning

confidence: 99%