Synergistic effect of oxygen vacancies and positively charged Ag clusters on Ag/CeO2 for efficient carboxylation of terminal alkynes with CO2

The carboxylation of alkynes with CO2 has attracted considerable interest due to the valorization of C1 resources and atomic economy. Much effort focused on active metals (e.g., Au, Ag, Cu), while the mechanistic role of active supports, particularly the oxygen vacancy (Ov), in modulating C–H bond carboxylation remains unknown. Herein, ultra-small silver clusters and morphologically engineered CeO2 support (nanorods, nanocubes, and nanoparticles) were employed to construct Ag cluster/Ov synergistic catalyst, which exhibits variations in Ov concentration by an in situ auto-reduction method. The 0.197 %Ag/CeO2-NR catalyst exhibited a high reaction rate for the phenylacetylene carboxylation reaction and the maximal silver utilization efficiency. The characterization and DFT calculations demonstrated that vacancies enhanced CO2 adsorption via polarization-induced molecular bending and C–O bond elongation. Positively charged Ag clusters induced by metal-support interactions serve as deprotonation activation centers for alkynes. This synergistic interplay between dual active sites efficiently facilitates the C(sp)–H carboxylation with CO2. These findings offer critical insights for the rational selection of active supports in designing efficient C–H carboxylation catalysts.