Enhanced Performance of Palladium Catalyst Confined Within Carbon Nanotubes for Heck Reaction

Confined carbon nanotubes (CNTs) are typically used to tune the activity and stability of catalysts so as to increase their efficiency. Herein, we compared the catalytic performances of palladium nanoparticles (Pd NPs) located in different regions of CNTs for Heck reaction. The catalyst with Pd NPs located in the internal surface of CNTs (Pd-in-CNT) has a higher reaction rate than that with Pd NPs attached on the external surface of CNTs (Pd-out-CNT). The activity of the Pd-in-CNT is 9.4 times higher than that of Pd-out-CNT in the Heck reaction, possibly because of the smaller particle size and modified redox properties of the confined Pd NPs. The CNT cavities create more active sites, consistenting with a higher microcalorimetric adsorption of carbon monoxide. Leaching of the Pd species during the reactions was observed with both types of catalysts. However, the Pd-in-CNT catalyst showed lower leaching than that of Pd-out-CNT owing to the spatial restriction of the channels in the former. More importantly, these novel catalysts were also used to synthesize a broad range of p -substituted iodobenzene derivatives, affording new and efficient route for the synthesis of valuable fine chemicals via carbon–carbon bond cross-coupling reactions. Graphic Abstract