Zirconia-supported sodium-salt-modified Au(0) nanoparticles (NPs) (Na-Au/ZrO2) catalyst was prepared, and it was stable and recyclable in the intramolecular cyclization of alkynoic acids. In particular, the effect of sodium species in Na-Au/ZrO2, which has been overlooked in previous studies, was studied, and they were found to play an essential role in the reaction. In addition, the relationship between the kinetics and size of Au NPs revealed that the active sites of the catalyst are located on the surface of the supported Au NPs. Moreover, detailed kinetic studies revealed that the cyclization was a zero-order reaction with respect to substrate concentration, and the rate-determining step of the reaction is presumed to be protodeauration. The maximum turnover number (TON) of the reaction of 5-hexynoic acid in a continuous flow reactor exceeded 9000, which is the highest TON obtained in the presence of a heterogeneous Au catalyst.
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