The presence of electric fields may influence the reactivity, the dynamics and the structure of a catalyst, subsequently affecting the global efficiency of the catalytic process. However, there is currently a lack of understanding of field-assisted phenomena, and a systematic study is thus necessary using appropriate experimental techniques. The present abstract focusses on three different topics: the reconstruction of Pt nanosized particles in the presence of reactive gases; the “low” reactivity of Au-based catalysts; and the nonlinear behaviors on Pt samples. Experiments are mainly performed with field emission techniques, i.e. field emission microscopy (FEM) and field ion microscopy (FIM), in the presence of static electric fields in the 1-10 V/nm range. Correlative microscopies such as photoemission electron microscopy (PEEM), with electric fields in the 10-3 V/nm range, and in-situ scanning electron microscopy ESEM (in absence of electric field) are also used to highlight the effect the electric field on the catalytic processes. The first case study corresponds to surface reconstructions of Pt assisted by oxygen adsorption: gas exposure is performed at low (~10 Langmuir) and high doses (&gt; 100 L) in the temperature range 500-700 K in absence and presence of electric field. The FEM/FIM experiments suggest that the presence of an electric field may hinder the extension of certain facets, therefore influencing catalytic reconstruction-processes. The second case study focusses on the reactivity of Au-Ag catalysts for oxidation reactions. The ability to supply adsorbed oxygen is one key to provide activity/selectivity on gold surfaces. Different systems are studied: O2 hydrogenation and CO oxidation reactions are performed from room temperature to 400 K by FEM and from 300 to 450 K by PEEM. In both cases, the reactivity is relatively low, suggesting an insignificant effect of the field on these reactions. However, FIM and FEM experiments on N2O hydrogenation on Au-Ag samples highlight the presence of reactive behaviors in a narrow range of temperature. Finally, the last case evokes nonlinear behaviors during NO2 hydrogenation in the form of oscillations and propagation of chemical waves. Such behaviors are observed on nanosized Pt tips by FEM and FIM, but also on Pt single crystals and Pt foils by in situ SEM. The global dynamics remains the same, and the details (periodicity, robustness, …) suggest only a minor influence of the field for this system.

Experimental evidences of the effects of electric fields in catalysis

2019 Spring National Meeting

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