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Accueil > Séminaires > Année 2024 > Séminaire d’Enrique Ortega (5 mars)

Séminaire d’Enrique Ortega (5 mars)

Universidad del País Vasco, San Sebastian, Spain

par Martrenchard-Barra Séverine - 23 février

Simulating high-pressure surface reactions with molecular beams

Using a reactive molecular beam with high kinetic energy (Ekin) it is possible to speed gas-surface reactions involving high activation barriers (Eact), which would require elevated pressures (P0) if a random, Maxwell-Boltzmann gas is used. By simply computing the number of molecules that overcome the activation barrier in a random gas at P0 and in a molecular beam at Ekin=Eact, we establish a P0(Ekin) equivalence curve. Based on this curve, we postulate that molecular beams are ideal tools to investigate gas/surface reactions that involve high Eact, such as the activation of greenhouse gases (CH4 and CO2) on metal catalysts. In particular, we foresee the use of molecular beams to simulate the industrial-range in such reactions (>10 bar) while making use of X-ray photoemission spectroscopy (XPS). To test this idea, we revisit the oxidation of Cu(111) combining O2 molecular beams and XPS [1]. By tuning the kinetic energy of the O2 beam in the range 0.24-1 eV we achieve the same sequence of surface oxides obtained in Ambient Pressure Photoemission (AP-XPS) experiments, in which the Cu(111) surface was exposed to a random O2 gas up to 1 mbar. Moreover, we observe the same surface oxidation kinetics as in the random gas, but with a much lower dose, close to the expected value derived from the equivalence curve.

[1] A. Al Taleb et al. DOI : 10.1039/D3CP05071H.