Charge transfer dependence on CO₂ hydrogenation activity to methanol in Cu nanoparticles covered with metal-organic framework systems

We report the synthesis and characterization of highly active Cu nanoparticles covered with zirconium/hafnium-based metal-organic frameworks for CO₂ hydrogenation to methanol. Compared to Cu/γ-Al₂O₃, Cu/ZIF-8, Cu/MIL-100 and Cu/UiO-66 composites, UiO-66 acts as the most active support, with Cu/Zr-UiO-66 producing methanol at a rate 70 times higher than that of Cu/γ-Al₂O₃. In addition, the replacement of Zr⁴⁺ with Hf⁴⁺ in UiO-66 tripled in the rate of methanol production. Furthermore, we describe a substituent effect on the catalytic activity, with Cu/Zr-UiO66-COOH providing a three-fold enhancement of methanol production, compared to that of Zr-UiO-66 or Zr-UiO66-NH₂. The enhanced catalytic activity of Cu nanoparticles depends on the charge transfer degree from Cu nanoparticles to UiO-66 at the interface between Cu nanoparticles and UiO-66.