Datensatz

Zusammenfassung

In heterogeneous catalysis, a catalytic process takes place at nite temperature and at nite pressure of the atmosphere of the reactant gases. By applying ab initio atom- istic thermodynamics to the model case of free Au₂ and Au^-₂ clusters in an atmosphere of O₂ and CO, we derive all the thermodynamically possible reaction paths for the ox- idation of CO to COV. This analysis lets us explain how gold clusters enable oxidation reactions without breaking the spin-conservation rule. Furthermore, we identify special cluster+ligands compositions such as reaction intermediates and poisoned species. In particular, a thermodynamically driven poisoning is identied for the catalytic system containing free Au₂ , and the experimental (p; T) conditions that avoid its formation are suggested. This implies that for some systems a catalytic cycle can be established, on thermodynamics grounds, only in a dened range of temperatures and pressures. In addition, our predictions for Au^-₂ provide the so far most complete interpretation of the available experimental data [Socaciu et al, J. Am. Chem. Soc. 125, 10437 (2003)].