Effect of graphene with nanopores on metal clusters†
Porous graphene, which is a novel type of defective graphene, shows excellent potential as a support material for metal clusters. In this work, the stability and electronic structures of metal clusters (Pd, Ir, and Rh) supported on pristine graphene and graphene with different sizes of nanopores were investigated using first-principles density functional theory (DFT) calculations. Then, CO adsorption and oxidation on the Pd–graphene system were chosen to evaluate its catalytic performance. Graphene with nanopores can strongly stabilize the metal clusters and cause a substantial downshift of the d-band center of the metal clusters, thus decreasing CO adsorption. All binding energies, d-band centers, and adsorption energies show a linear change with the size of the nanopore: a bigger size of the nanopore corresponds to stronger bonding of metal clusters with graphene, lower downshift of the d-band center, and weaker CO adsorption. By using a suitable size nanopore, Pd clusters supported on graphene will have similar CO and O2 adsorption abilities, thus leading to superior CO tolerance. The DFT calculated reaction energy barriers show that graphene with nanopores is a superior catalyst for CO oxidation reaction. These properties can play an important role in instructing graphene-supported metal catalyst preparation to prevent the diffusion or agglomeration of metal clusters and enhance the catalytic performance.