Tailoring Cu-SiO2 Interaction through Nanocatalyst Architecture to Assemble Surface Sites for Furfural Aqueous-Phase Hydrogenation to Cycloketones.

In this contribution, nanocatalysts with rather diverse architectures were designed to promote different intimacy degrees between Cu and SiO₂ and consequently tune distinct Cu-SiO₂ interactions. Previously synthesized copper nanoparticles were deposited onto SiO₂ (NPCu/SiO₂) in contrast to ordinarily prepared supported Cu/SiO₂. NPCu@SiO₂ and SiO₂@Cu core-shell nanocatalysts were also synthesized, and they were all bulk and surface characterized by XRD, TGA, TEM/HRTEM, H₂-TPR, XANES, and XPS. It was found that Cu⁰ is the main copper phase in NPCu/SiO₂ while Cu²⁺ rules the ordinary Cu/SiO₂ catalyst, and Cu⁰ and electron-deficient Cu^δ+ species coexist in the core-shell nanocatalysts as a consequence of a deeper metal-support interaction. Catalytic performance could not be associated with the physical properties of the nanocatalysts derived from their architectures but was associated with the more refined chemical characteristics tuned by their design. Cu/SiO₂ and NPCu/SiO₂ catalysts led to the formation of furfuryl alcohol, evidencing that catalysts holding weak or no metal-support interaction have no significant impact on product distribution even in the aqueous phase. The establishment of such interactions through advanced catalyst architecture, allowing the formation of electron-deficient Cu^δ+ moieties, particularly Cu²⁺ and Cu⁺ as unveiled by spectroscopic investigations, is critical to promoting the hydrogenation-ring rearrangement cascade mechanism leading to cycloketones.