Photocatalytic Reduction of CO₂ to CO in 100%: The Synergistic Effect of Nickel and Europium in Heterometallic Clusters

Heterometallic transition-rare earth metal (3d-4f) clusters with synergistic catalytic activity are rarely identified. Herein, two families of closely related 3d-Eu clusters were designed to analyze the role of Eu(III) ions during the photocatalytic reduction of CO₂ into CO. The [M₂₄Eu₈] family, where M = Co or Ni, shows much lower activity (CO production < 2078 µmol g⁻¹ h⁻¹) compared to the [M₂₄Eu₁₀] family (CO production > 5838 µmol g⁻¹ h⁻¹). This is due to the two additional Eu(III) ions in the apical position of the latter which are very active for converting CO₂ into CO. Moreover, we found the nickel analogues are better than the cobalt ones, especially for [Ni₂₄Eu₁₀] which exhibits 100% CO selectivity and very high efficacy of 6545.3 µmol g⁻¹ h⁻¹, while the [Co₂₄Eu₁₀] only shows 55% CO selectivity. Therefore, the coexistence of both apical Eu(III) and Ni(II) ions has been experimentally revealed to be critical for this exceptional catalytic performance of the [Ni₂₄Eu₁₀] cluster. As such, this work unambiguously reveals a synergistic effect of bimetallic catalysts and may open a new avenue for more sophisticated reaction design by using the heterometallic coordination clusters.