Energy-pooling transitions to doubly excited K atoms at a promoted iron-oxide catalyst surface: more than 30 eV available for reaction

The promoter action of alkali atoms, such as K atoms, at heterogeneous catalyst surfaces has been used in industrial catalysis for many decades, giving improved activity and selectivity in the catalyzed chemical reactions. Several mechanisms for this promotion effect have been proposed, among which the Rydberg excitation mechanism is well-supported by experiments from our groups. Further experiments now show that even doubly excited K Rydberg species are formed at an industrial catalyst (styrene catalyst) surface. This indicates that a large excitation energy of >30 eV can easily accumulate in an atomic or molecular species. The methods used for the identification of the excited species are pulsed laser-induced TOF-MS and intracavity stimulated emission. The doubly excited states are formed at the surface of the catalyst by thermal excitation through selective excitation and energy-pooling processes and are here observed outside the surface in the extended boundary layer. Experiments with ionization energy transfer indicate that no energy matching is required in reactions driven by the excitation energy.