Structure Sensitivity of NO Adsorption–Dissociation on Pdn (n = 8, 13, 19, 25) Clusters

Abstract

NO adsorption and dissociation on subnanometer Pdn (n = 8, 13, 19, 25) clusters were first studied with GGA-DFT. The transition structures of the NO dissociating on the potential-energy surfaces were derived using the climbing image nudged-elastic-band (CI-NEB) method. The preferred NO adsorption positions are bridge sites on Pdn (n = 8, 19) and hollow sites on Pdn (n = 13, 25). The NO adsorption energy values on hollow sites of icosahedron-based Pdn (n = 13, 25) are relatively higher than that on the bridge site of octahedral Pd19. However, the NO dissociation barrier on octahedral Pd19 is lower than that on icosahedron-based Pdn (n = 13, 25) clusters. These results suggest on a Pdn (n = 8, 13, 19, 25) scale the NO activity may no longer rely on the cluster size but rather on the geometric structure of Pdn clusters. The coordination number of the NO adsorption site is found to be the key factor to determine the structure sensitivity of NO adsorption and dissociation. The charge difference and Hirshfeld charges reveal that the charge transfer is from the Pdn clusters to NO and increases upon NO dissociation. PDOS reveals that the 3σ, 4σ, 5σ, 1π, and 2π peaks of NO are sensitive not to Pdn cluster size but to NO adsorption sites. Our calculations may provide an insight into structure-sensitive Pd-based catalysts for NO removal on a subnanometer scale.