Gold Nanoparticles Catalyzed Hydrogen Dissociation:A Theoretical Study

Hydrogen(H2)is a prospective clean energy and a good energy carrier.Hydrogen fuel cell is also widely studied.There are plenty of chemical reactions associated with H2 as a reactant.Thus the mechanism of H2 dissociation is important to further investigate the mechanism of those reactions.Although the gold was once thought to be the noblest metal,the catalytic activity of gold nanoparticles(GNPs)has been recognized with the development of nanotechnology.The H2 is prone to dissociate on GNPs,while only interacts with gold surfaces weakly.So the H2 dissociation is a desirable model to inspect the catalytic mechanism of GNPs.By adopting a gold cluster model,we studied the mechanism of gold-catalyzed H2 dissociation through the DFT-B3LYP method.(1)GNPs catalyzed H2 dissociation.On the basis of simulating the active sites on GNPs through gold clusters,the H2 dissociation paths on gold clusters were calculated.Comparing with the dissociated states that proposed in previous works and most stable structures of the hydrogen atom adsorbed on the same gold clusters,the H2 dissociation paths proposed in this thesis are a multi-step process.Our calculated activation energy,reaction energy,and rate constant imply that the gold cluster model is reasonable and suitable.Analyzing the natural bonding orbital(NBO)charge distribution and density of states indicates that the H2 dissociation mechanism on gold clusters is proved to be a reverse Tafel process.(2)GNPs photocatalyzed H2 dissociation.GNPs display strong surface plasmon resonance(SPR).To investigate the SPR induced H2 dissociation mechanism on GNPs,we calculated the H2 dissociation paths on GNPs at low-lying electronic excited states.There is no electron transfer between gold clusters and H2,so the mechanism still is a reverse Tafel process for SPR induced H2 dissociation on GNPs.The natural transition orbital(NTO)analysis reveals that the decrease of activation energy is due to the change of electron cloud of the gold cluster at some excited states.(3)GNPs electrocatalyzed H2 dissociation.The effect of solvent water was taken into accounts in this thesis to inspect the mechanism of GNPs electrocatalyzed H2 dissociation.Water molecules play as assisted catalyst and decrease the reaction barriers of the H2 dissociation on gold clusters.It is an oxidation process for water assisted H2 dissociation on gold clusters.