SiO2-Coated Ag Nanoparticles for Conversion of Terminal Alkynes to Propolic Acids via CO2 Insertion

Integration of adequate activity, stability, and productivity in a catalyst is of strategical importance to achieve high performance, particularly for inactive reactants, e.g., CO2. Here, using a reversed microemulsion method, ultrafine metallic Ag nanoparticles coated with porous SiO2 can be facilely obtained using micelles as separated nanoreactors for the preparation. Such architectures allowed the rigid SiO2 matrices to act as physical spacers, so that aggregation of the Ag particles could be avoided. Meanwhile, due to the templating effect from the surfactant, large mesopores could be induced in the SiO2 shell, and thus the diffusion barrier of reactants could be minimized. When used as a heterogeneous catalyst for carboxylation of terminal alkynes by CO2 under mild conditions, the prepared xAg@SiO2 catalysts showed extraordinary performance in terms of excellent activity, stability, productivity, and wide substrate scope. The knowledge developed here may also enrich the toolbox for performance promotion of metal catalysts via specially fabricated structures.