Exploring the Chemical Reactivity between Carbon Dioxide and Three Transition Metals (Au, Pt, and Re) at High-Pressure, High Temperature Conditions

The role of carbon dioxide, CO2, as oxidizing agent at high pressures and temperatures is evaluated by studying its chemical reactivity with three transition metals: Au, Pt, and Re. We report systematic X-ray diffraction measurements up to 48 GPa and 2400 K using synchrotron radiation and laser-heating diamond-anvil cells. No evidence of reaction was found in Au and Pt samples in this pressure temperature range. In the Re + CO2 system, however, a strongly driven redox reaction occurs at P > 8 GPa and T > 1500 K, and orthorhombic beta-ReO2 is formed. This rhenium oxide phase is stable at least up to 48 GPa and 2400 K and was recovered at ambient conditions. Raman spectroscopy data confirm graphite as a reaction product. Ab-initio total-energy structural and compressibility data of the beta-ReO2 phase shows an excellent agreement with experiments, altogether accurately confirming CO, reduction P T conditions in the presence of rhenium metal' and the beta-ReO2 equation of state.