CO oxidation on h-BN supported Au atom

Abstract

The mechanism of CO oxidation by O 2 on Au atoms supported on the pristine and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. It is found that O 2 binds stronger than CO on an Au atom supported on the defect free h-BN surface and h-BN surface with nitrogen vacancy (V N @h-BN), but weaker than CO on a free Au atom or Au trapped by a boron vacancy (V B @h-BN). The excess of the positive or negative charge on Au can considerably change its catalytic properties and enhance activation of the adsorbed O 2 . Coadsorption of CO and O 2 on Au, Au/V N @h-BN, and Au/V B @h-BN results in additional charge transfer to O 2 . Various pathways of the CO oxidation reaction by molecular oxygen are studied. We found two different pathways for CO oxidation: a two-step pathway where two CO 2 molecules are formed independently, and a self-promotion pathway where oxidation of the first CO molecule is promoted by the second CO molecule. Interaction of Au with the defect-free and defected h-BN surface considerably affects the CO oxidation reaction pathways and barriers. Therefore, Au supported on the h-BN surface (pristine or defected) cannot be considered as pseudo-free atom and support effects have to be taken into account, even when the interaction of Au with the support is weak.

Adsorption and Catalytic Activation of the Molecular Oxygen on the Metal Supported h-BN

“…The starting structures have been optimized without any geometry constraints. The similar approach has been successfully used in our previous works for oxygen reduction reaction on the N-doped h-BN monolayer [13], on adsorption of O 2 , H 2 , and C 2 H 4 molecules on the free and supported gold clusters [11,12,16,17,19,59,60] as well as on molecular and cluster structure optimization [61][62][63][64][65].…”

“…Moreover, the WC functional gives a realistic description of the binding energies and geometries of h-BN layer on top of 3d, 4d and 5d transition metal surfaces, correctly describing the interaction of transition metals with h-BN [37,44,45]. The WC functional was successfully used in our previous works to describe ORR on N-doped h-BN monolayer [13], and catalytic activity of small gold particles on the pristine and defected h-BN surfaces [16,17,19]. [46,47].…”

“…According to the Bader analysis, the charge localized on the O 2 adsorbed in on-top configuration is -0.92e, where e is an elementary charge. Such mechanism of the charge-transfer-mediated activation of O 2 has been intensively studied for O 2 adsorbed on metal clusters; see, e.g., refs [11,16,17,19,[21][22][23][24][25][26][27] and references therein. Adsorption of O 2 on h-BN/Ni(111) in a bridge configuration results in a further population of the down-spin 2π * orbital which becomes completely occupied and lies below the Fermi level.…”

“…Strong adsorption on the surface defects is accompanied by the charge transfer to/from the adsorbate which can affect the catalytic activity of gold [18]. It has been shown that interaction of Au with the h-BN surface can affect considerably the pathways and barriers of CO oxidation reaction by molecular oxygen [19]. Moreover, adsorption, activation and dissociation of O 2 on h-BN supported gold atoms and dimers can be affected even by the interaction with the defect-free inert h-BN support via the electron pushing mechanism [16][17][18].…”

Analyses of bifurcation of reaction pathways on a global reaction route map: A case study of gold cluster Au5

“…In the present study, the bifurcation analyses of the IRC are combined with GRRM computations, and the appearance of VRT in the global reaction route map and the connection of VRT with additional product minimum are examined for a small gold cluster, Au 5 . Since the pioneer work of Haruta et al, 35 gold clusters have been paid attention extensively [36][37][38] due to a large interest in its unique catalytic activity. Au 5 is a very interesting species as a target because plural symmetrically equivalent paths exist due to a high symmetry of the system.…”