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

Abstract 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 CO 2 into CO. The [M 24 Eu 8 ] family, where M = Co or Ni, shows much lower activity (CO production < 2078 µ mol g −1 h −1 ) compared to the [M 24 Eu 10 ] family (CO production > 5838 µ mol 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 CO 2 into CO. Moreover, we found the nickel analogues are better than the cobalt ones, especially for [Ni 24 Eu 10 ] which exhibits 100% CO selectivity and very high efficacy of 6545.3 µ mol g −1 h −1 , while the [Co 24 Eu 10 ] 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 [Ni 24 Eu 10 ] 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.