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Herve Toulhoat

Publications and source records attributed to Herve Toulhoat.

2 recordsLinked to original sources

Prediction of optimal catalysts for a given chemical reaction

We reveal a correlation between the M-X bond energy descriptor EMX for the optimal catalyst in a family of stoichiometry MiXj, and an intensive quantity defined as the standard enthalpy of the catalyzed reaction normalized to one mole of element X transferred by this reaction from reactants to products. M is a transition element, and the stoichiometry MiXj is fixed at the solid/fluid interface by the reaction conditions. We illustrate this for a relevant set of reactions involved in solar energy and industrial applications such as oxygen evolution, oxygen reduction and hydrogen evolution in electrolysis, hydrodesulfurization of thiophene, methanation of CO, hydrogenations of aromatics and alkenes, selective oxidation of methane, and ammonia synthesis and decomposition. We propose a quantitative model to explain this unexpected connection: this key finding and its interpretation should accelerate in silico discovery of catalysts.

cond-mat.mtrl-sci

Chemical differentiation of planets: a core issue

By plotting empirical chemical element abundances on Earth relative to the Sun and normalized to silicon versus their first ionization potentials, we confirm the existence of a correlation reported earlier. To explain this, we develop a model based on principles of statistical physics that predicts differentiated relative abundances for any planetary body in a solar system as a function of its orbital distance. This simple model is successfully tested against available chemical composition data from CI chondrites and surface compositional data of Mars, Earth, the Moon, Venus, and Mercury. We show, moreover, that deviations from the proposed law for a given planet correspond to later surface segregation of elements driven both by gravity and chemical reactions. We thus provide a new picture for the distribution of elements in the solar system and inside planets, with important consequences for their chemical composition. Particularly, a 4 wt% initial hydrogen content is predicted for bulk early Earth. This converges with other works suggesting that the interior of the Earth could be enriched with hydrogen.

astro-ph.EP