Stepwise assembly of thiacalix[4]arene-protected Ag/Ti bimetallic nanoclusters: accurate identification of catalytic Ag sites in CO(2) electroreduction

The accurate identification of catalytic sites in heterogeneous catalysts poses a significant challenge due to the intricate nature of controlling interfacial chemistry at the molecular level. In this study, we introduce a novel strategy to address this issue by utilizing a thiacalix[4]arene (TC4A)-protected Ti-oxo core as a template for loading Ag(1+) ions, leading to the successful synthesis of a unique Ag/Ti bimetallic nanocluster denoted as Ti(8)Ag(8). This nanocluster exhibits multiple surface-exposed Ag sites and possesses a distinctive “core–shell” structure, consisting of a {Ti(4)@Ag(8)(TC4A)(4)} core housing a {Ti(2)O(2)@Ag(4)(TC4A)(2)} motif and two {Ti@Ag(2)(TC4A)} motifs. To enable a comprehensive analysis, we also prepared a Ti(2)Ag(4) cluster with the same {Ti(2)O(2)@Ag(4)(TC4A)(2)} structure found within Ti(8)Ag(8). The structural disparities between Ti(8)Ag(8) and Ti(2)Ag(4) provide an excellent platform for a comparison of catalytic activity at different Ag sites. Remarkably, Ti(8)Ag(8) exhibits exceptional performance in the electroreduction of CO(2) (eCO(2)RR), showcasing a CO faradaic efficiency (FE(CO)) of 92.33% at −0.9 V vs. RHE, surpassing the FE(CO) of Ti(2)Ag(4) (69.87% at −0.9 V vs. RHE) by a significant margin. Through density functional theory (DFT) calculations, we unveil the catalytic mechanism and further discover that Ag active sites located at {Ti@Ag(2)(TC4A)} possess a higher ε(d) value compared to those at {Ti(2)O(2)@Ag(4)(TC4A)(2)}, enhancing the stabilization of the *COOH intermediate during the eCO(2)RR. This study provides valuable insights into the accurate identification of catalytic sites in bimetallic nanoclusters and opens up promising avenues for efficient CO(2) reduction catalyst design.