STM and DFT Study of Chlorine Adsorption on the Ag(111)-p(4 × 4)–O Surface

Abstract

Coadsorption of chlorine and oxygen on the Ag(111) surface has been studied with low-temperature scanning tunneling microscopy in combination with density functional theory calculations. Room-temperature adsorption of chlorine onto the Ag(111)-p(4 × 4)–O surface leads to the appearance of new bright objects located between protrusions of the 4 × 4 reconstruction. As chlorine adsorbs, objects form “rosettes” around corner holes. This configuration coincides with the configuration of the chlorine atoms in the Ag(111)-(3 × 3)–Cl reconstruction structure. We conclude that the adsorption of chlorine on the Ag(111)-p(4 × 4)–O surface occurs dissociatively, with chlorine atoms displacing oxygen atoms from the 4-fold positions. Adsorption of chlorine at 77 K results in the formation of the mixed Cl–O species on the Ag6 triangles of the p(4 × 4) reconstruction. Both scenarios of chlorine adsorption are unexpected and cannot be explained within a commonly accepted Ag6 model of the p(4 × 4) reconstruction.

Unravelling the key factors in the chlorine-promoted epoxidation of ethylene over a silver–copper oxide nanocatalyst

“…In the case of Ag(111) surfaces evaluated in previous studies, Cl atoms have been found in subsurface layers by STM and predicted in DFT calculations. 29,33–35,43 This is also the case for the AgCuO catalyst, where Cl was experimentally detected in the subsurface layers after XPS etching. 44 Finally, to complete these models, we also took into consideration that an O 2 molecule is dissociated and chemisorbed on the catalyst surface in the first step of the ethylene epoxidation reaction.…”

“…44 Finally, to complete these models, we also took into consideration that an O 2 molecule is dissociated and chemisorbed on the catalyst surface in the first step of the ethylene epoxidation reaction. 35…”

“…44 Finally, to complete these models, we also took into consideration that an O 2 molecule is dissociated and chemisorbed on the catalyst surface in the first step of the ethylene epoxidation reaction. 35 Accordingly, we started from a single AgO atomic pair on top of a CuO(111) surface. The slab lattice parameters (a, b and c lengths) were 8.65, 12.28 and 23.24 Å, respectively.…”

“…). [24][25][26][27][28][29][30][31] Moreover, chlorine gas is added to the reaction mixture as a promoter to increase the selectivity towards EO production, 14,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] further complicating the understanding of the process. In the case of chlorine atoms on Ag surfaces, it has been predicted that a decrease of the energy barriers 31 and an increase of the EO desorption energy will minimize its total oxidation.…”

Chlorine Adsorption on the Ag(110) Surface: STM and DFT Study

“…4,28−33 However, structural models of coadsorption structures have not been obtained in most cases. There is only one STM study 33 As for the Ag(110) face, two ordered oxide-like structures were reported, p(2 × 1) and c(6 × 2), 34 whose structural models are considered to be proved. Regarding the adsorption of chlorine on Ag(110), in contrast to the (111) face, the system remains unstudied by scanning tunneling microscopy.…”