Hochdruck-Niederenergie-Röntgenabsorptionsspektroskopie: ein Beitrag zur Überwindung des „pressure gaps” in der Untersuchung heterogenkatalytischer Prozesse

Abstract

Erstmals wurde unter Praxisbedingungen durch oberflächenempfindliche Röntgenabsorption im Bereich der weichen Röntgenstrahlung am Beispiel der Methanoloxidation an Kupfer eine aktive Oberflächenphase charakterisiert und ihre Funktion mit der katalytischen Aktivität des Systems korreliert. Es handelt sich bei dieser Phase nicht um an der Oberfläche adsorbierten Sauerstoff (linkes Bild, O = schwarze Kugeln), sondern um ein im oberflächennahen Bereich gebildetes Kupfersuboxid (rechtes Bild).

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“…The shift in the white line maxima between bulk Cu 2 O and the ox phase may be accounted for by the presence of a still metallic substrate in the ox phase. From previous experiments [7,8,17] we know that the ox phase develops into bulk oxide upon sufficient exposure to gas phase oxygen. The chemical bonding of oxygen in the ox phase and in the bulk oxide are similar.…”

“…The experiments are performed in a new constructed reactor cell [4,7,8]. The used UHV-system consists out of two stainless steel chambers.…”

“…In Ref. [7] the formation of Cu 2 O and CuO was investigated by detecting in-situ NEXAFS spectra at the Cu L 2,3 -edges during heating of a copper foil at 600 K in 0.05 and 0.1 mbar oxygen atmosphere, respectively. In the present communication the electronic structure of the copper catalyst surface and the composition of the gas phase are detected simultaneously under steady state methanol oxidation reaction conditions.…”

In Situ Investigation of the Nature of the Active Surface of a Vanadyl Pyrophosphate Catalyst during n-Butane Oxidation to Maleic Anhydride

“…The XAS experiments were performed using a special reactor cell designed for in situ X-ray absorption investigation. Details about the setup and the data processing can be found in the literature. − For the in situ experiments, a continuous flow of 1.5 vol % n -butane in He balance and oxygen were dosed via two calibrated mass flow controllers at a total mass flow of 17.5 sccm. The partial pressures of the n -C 4 H 10 /He mixture and the oxygen were 1.6 and 0.4 mbar, respectively, resulting in a total pressure in the reactor of 2 mbar during the XAS measurements.…”