August 31, 2020

On the Promotion of Catalytic Reactions by Surface Acoustic Waves

B. von Boehn, M. Foerster, J. Prat , F. Macià, B. Casals, M. Waqas Khaliq, A. Hernández-Mínguez, L. Aballe,  R. Imbih

Angewandte 2020

DOI: 10.1002/anie.202005883 


Surface acoustic waves (SAW) allow to manipulate surfaces with potential applications in catalysis, sensor and nanotechnology. SAWs were shown to cause a strong increase in catalytic activity and selectivity in many oxidation and decomposition reactions on metallic and oxidic catalysts. However, the promotion mechanism has not been unambiguously identified. Using stroboscopic X‐ray photoelectron spectro‐microscopy we were able to evidence a sub‐nanosecond work function change during propagation of 500 MHz SAWs on a 9 nm thick platinum film. We quantify the work function change to 455 µeV. Such a small variation rules out that electronic effects due to elastic deformation (strain) play a major role in the SAW‐induced promotion of catalysis. In a second set of experiments SAW‐induced intermixing of a five monolayers thick Rh film on top of polycrystalline platinum was demonstrated to be due to enhanced thermal diffusion caused by an increase of the surface temperature by about 75 K when SAWs were excited. Reversible surface structural changes are suggested to be a major cause for catalytic promotion.



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