Hydrogenation of carbon dioxide to methanol over molybdenum catalysts.

The hydrogenation of carbon dioxide was done over molybdenum-based catalyst s prepared by impregnation (supported) or precipitation (bulk). Indeed the redox properties of molybdenum associated with a specific hydrogen activati on can lead to a 'complexation-activation' state of CO2 which allows the me thanol synthesis. The study of [molybdenum-support(ceria, active carbon, ti tania, zinc oxide or carbonate)] catalysts showed that zinc oxide definitel y increased the selectivity and the yield to methanol. On the other hand, c ontrary to what was observed in the (CO, H-2) reaction, the selectivity and the rate of methanol formation from (CO2, H-2) are not very dependent of a dditives such as alkaline or activation processes. This result shows that t he rate-limiting steps of the two reactions are different. The redox state of molybdenum and the hydrogen activation are modified after addition of co pper and formation of a bulk ternary [Cu-Mo-Zn] catalyst. It results in an increase of the rate of CO2 conversion co methanol. The formation of mixed [Cu-Mo-x] species stabilized and dispersed over zinc oxide (from DRX, TPR a nd XPS) could be involved in the reaction. (C) Academie des sciences/Elsevi er, Paris.