Coordination-Induced Trigger for Activity: N-Heterocyclic Carbene-Decorated Ceria Catalysts Incorporating Cr and Rh with Activity Induction by Surface Adsorption Site Control

A coordination-induced trigger for catalytic activity is proposed on an N-heterocyclic carbene (NHC)-decorated ceria catalyst incorporating Cr and Rh (ICy-r-Cr0.19Rh0.06CeOz). ICy-r-Cr0.19Rh0.06CeOz was prepared by grafting 1,3-dicyclohexylimidazol-2-ylidene (ICy) onto H2-reduced Cr0.19Rh0.06CeOz (r-Cr0.19Rh0.06CeOz) surfaces, which went on to exhibit substantial catalytic activity for the 1,4-arylation of cyclohexenone with phenylboronic acid, whereas r-Cr0.19Rh0.06CeOz without ICy was inactive. FT-IR, Rh K-edge XAFS, XPS, and photoluminescence spectroscopy showed that the ICy carbene-coordinated Rh nanoclusters were the key active species. The coordination-induced trigger for catalytic activity on the ICy-bearing Rh nanoclusters could not be attributed to electronic donation from ICy to the Rh nanoclusters. DFT calculations suggested that ICy controlled the adsorption sites of the phenyl group on the Rh nanocluster to promote the C-C bond formation of the phenyl group and cyclohexenone.