(242b) Systematic Studies of Catalyst Structure-Property Relationships in CO2 Hydrogenation to Methanol

The research focus on converting CO₂ to methanol is favored due to the ease of methanol transportation and its versatility as a fuel or intermediate for valuable chemical production. Copper-based catalysts have been extensively studied in CO₂ hydrogenation and are considered one of the most promising catalysts due to their high performance and low cost. However, identifying the precise active sites for various products in copper-based catalysts proves challenging due to the intricate coordination structure of copper species. In this work, we establish the role that different metal coordination environments play in catalytic activity and selectivity in CO₂ hydrogenation to methanol. A new library of well-defined Cu nanocrystals was prepared by high-temperature thermal decomposition of organometallic precursors, leading to a final nanocrystal library with different sizes of 6, 8 and 15 nm. It was observed that catalysts with bigger size showed slightly higher TOFs on methanol production. We therefore expect that the number of the most active-site atoms will follow a similar continuous increase as nanoparticle sizes increase. Cu nanoparticles synthesized in this project have a face-centered cubic structure and a cuboctahedra shape that exposes (100) and (111) facets. The surface typically exhibits two distinct types of atoms, characterized by their coordination numbers (CN) as step-edges (CN: 5–7) and terraces (CN: 8–9). Among the considered active sites, the size dependency for the number of terrace sites closely corresponds to the size dependency of the experimental TOF. This similarity explicitly indicates that terrace sites serve as the predominant active sites for methanol production. The higher TOFs can be explained because of a greater numbers of edge sites that facilitate CO formation due to stronger C-Cu bonds. Methanol is relatively difficult to form on the low-coordinated Cu sites due to its weak affinity to CO₂.