Perpustakaan Digital ITB

In this study, graphene nanosheet-supported ultrafine Cunanoparticles (NPs) encapsulated with thin mesoporous silica (Cu?GO@m-SiO2) materials are fabricated with particle sizes ranging from 60 to 7.8 nm andare systematically investigated for the oxidative coupling of amines to producebiologically and pharmaceutically important imine derivatives. Catalytic activityremarkably increased from 76.5% conversion of benzyl amine for 60 nm NPs to99.3% conversion and exclusive selectivity ofN-benzylidene-1-phenylmethan-amine for 7.8 nm NPs. The superior catalytic performance along with theoutstanding catalyst stability of newly designed catalysts are attributed to theeasy diffusion of organic molecules through the porous channel of mesoporousSiO2layers, which not only restricts the restacking of the graphene nanosheetsbut also prevents the sintering and leaching of metal NPs to an extreme extentthrough the nanoconfinement effect. Density functional theory calculationswere performed to shed light on the reaction mechanism and to give insightinto the trend of catalytic activity observed. The computed activation barriers of all elementary steps are very high on terraceCu(111) sites, which dominate the large-sized Cu NPs, but are significantly lower on step sites, which are presented in higherdensity on smaller-sized Cu NPs and could explain the higher activity of smaller Cu?GO@m-SiO2samples. In particular, theactivation barrier for the elementary coupling reaction is reduced from 139 kJ/mol onflat terrace Cu(111) sites to the feasiblevalue of 94 kJ/mol at step sites, demonstrating the crucial role of the step site in facilitating the formation of secondary imineproducts.KEYWORDS