Paper SS3-TuA4
A DFT Study of Methanol Synthesis by CO₂ Hydrogenation on Cu Nanoparticles and Surfaces

Tuesday, November 10, 2009, 3:00 pm, Room N

The synthesis of methanol from CO₂ and H₂ (CO₂+3H₂→CH₃OH+H₂O) has attracted considerable attention. It is not only environmentally important due to its application in the conversion of greenhouse gas, CO₂, it is also of great industrial significance because the product, methanol, can serve as a raw material for the synthesis of other organic compounds, besides being used as a liquid fuel. Commercially, the reaction is performed on a catalyst containing Cu, ZnO and Al₂O₃ at a high temperate (220-240°C) and high pressure (50-100 bar). There is a need to understand the reaction mechanism in order to develop more active and selective catalysts even though the mechanism is still controversial. In this study, density functional theory (DFT) was employed to elucidate the reaction mechanism on the Cu(111) surface and the promotion effect of nano-size Cu compared to bulk Cu.

Cu₂₉ nanoparticles, exposing a combination of (100) and (111) faces in a pyramidal structure, is the model we used to study the reaction pathways on the Cu nanoparticles. For comparison, the reaction mechanism on the Cu(111) surface is also studied. It was found out that on both systems, the reaction undergoes via formate (HCOO) and dioxomethylene (H₂COO). The reaction rate is controlled by hydrogenation of HCOO and H₂COO. In accordance with experimental findings, our results show that the Cu₂₉ nanoparticles display a superior activity over Cu(111). The better behavior of Cu₂₉ is associated with the low-coordinated Cu sites, which provide a reasonably strong binding to the intermediates.