Hybrid nanocomposite materials with synergies between different components show distinguished performance in optics,electronics,catalysis,and other applications.To gain more insights on the recently discovered enhanced catalytic performance of sub-nanosized transition metal nanostructures deposited on several 2D substrates,including reduced graphene oxide and layered silicides,we investigated the electronic structure of these composites first-principles-based calculations.We showed that transition metal nanoparticles prefer to bind directly with the localized defective structures on these substrates,which act as strong trapping sites for the nanostructures and inhibit their aggregation.We also showed that the binding of nanostructures to these substrates,which correlates with the interfacial structures and the charge transfer,tunes the averaged d-band center of the nanocomposites and contributes to improved reactivity of these composites.Further study reveals that the performance of the nanocomposites against oxygen reduction,arene hydrogenation and hydrodesulphurization correlates well with the shift of the d-band center of the nanostructures.These findings paved the way for developments of new transition metal nanocomposites with high stability and superior catalytic performance.