▎ 摘　　要

In heterogeneous catalysis, graphitic carbon formed on metal often poisons metal-catalyzed reactions through physical blockage of surface active sites. In materials science, recent works show that graphene overlayers can passivate metal surfaces acting as gas-impermeable protection coatings. However, here we show using in situ surface electron microscopy and photoemission spectroscopy that CO can be readily trapped inside the two-dimensional space between the graphene overlayer and Ru(0001) surface under near-ambient conditions. The intercalated CO molecules effectively decouple the graphene overlayer from the Ru substrate. Meanwhile, the graphene cover exerts a strong confinement effect on the surface chemistry of CO on Ru(0001), showing that a high-coverage CO adlayer can be kept at the graphene/Ru interface at room temperature which desorbs intensively and completely around 390 K. This finding challenges the traditional concept of graphene films as passivation layers, indicating that the surface graphitic carbon can be used to modify the surface chemistry of metals.