Isolated Zr Surface Sites on Silica Promote Hydrogenation of CO 2 to CH 3 OH in Supported Cu Catalysts.

Copper nanoparticles supported on zirconia (Cu/ZrO ₂ ) or related supported oxides (Cu/ZrO ₂ /SiO ₂ ) show promising activity and selectivity for the hydrogenation of CO ₂ to CH ₃ OH. However, the role of the support remains controversial because most spectroscopic techniques provide information dominated by the bulk, making interpretation and formulation of structure-activity relationships challenging. In order to understand the role of the support and in particular of the Zr surface species at a molecular level, a surface organometallic chemistry approach has been used to tailor a silica support containing isolated Zr(IV) surface sites, on which copper nanoparticles (∼3 nm) are generated. These supported Cu nanoparticles exhibit increased CH ₃ OH activity and selectivity compared to those supported on SiO ₂ , reaching catalytic performances comparable to those of the corresponding Cu/ZrO ₂ . Ex situ and in situ X-ray absorption spectroscopy reveals that the Zr sites on silica remain isolated and in their +4 oxidation state, while ex situ solid-state nuclear magnetic resonance spectroscopy and catalytic performances show that similar mechanisms are involved with the single-site support and ZrO ₂ . These observations imply that Zr(IV) surface sites at the periphery of Cu particles are responsible for promoting CH ₃ OH formation on Cu-Zr-based catalysts and provide a guideline to develop selective CH ₃ OH synthesis catalysts.