Formation and Behavior of Carbonates on Ag(110) in the Presence of Ethylene and Oxygen

Abstract

Intermediate species formed on Ag(110) surfaces under the presence of ethylene and oxygen in the sub-Torr pressure range were studied by near-ambient-pressure X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) measurements. Carbonates are clearly observed exclusively under an ethylene-rich condition (0.2 Torr ethylene and 0.04 Torr oxygen; ethylene/oxygen = 5) at a high temperature of 500 K or relatively low-temperature conditions (≤470 K) at an oxygen-rich gas ratio (ethylene/oxygen = 1/5). NEXAFS results support the formation of carbonates and indicate that the carbonates are adsorbed almost parallel to the Ag(110) surface. The carbonates coexist with surface oxides with different composition ratios depending on the ethylene/oxygen pressure ratio and surface temperature. From these results we propose that the carbonates are formed by reaction(s) between ethylene and oxygen on the Ag(110) surface.

Nature and Reactivity of Oxygen Species on/in Silver Catalysts during Ethylene Oxidation

“…24 The relative stability of the Na 2 CO 3 nanoparticles allowed using the carbonate bands at 1060−1078 cm −1 as an internal standard for normalization of the in situ Raman spectra. 25 The evolution of the integrated areas of the various oxygen species during in situ Raman measurements are presented in Figure S13. To avoid coincidence from surface inhomogeneity and confirm the trend of the observations, Raman spectra were also collected at a second spot and plotted in Figure S14 for reproducibility.…”

“…It should be noted that the signal to noise ratio of the Raman spectra dramatically decreased at T > 200 °C, possibly from some loss of surface roughness that decreases the SERS effect . The relative stability of the Na 2 CO 3 nanoparticles allowed using the carbonate bands at 1060–1078 cm –1 as an internal standard for normalization of the in situ Raman spectra . The evolution of the integrated areas of the various oxygen species during in situ Raman measurements are presented in Figure S13.…”

Promotional Effect of Ag on the Catalytic Decomposition of N2O in the Presence of O2 over the Al2O3-Supported Rh Catalyst

“…The Ag 3d AP-XPS spectra of RhO x /Ag/Al 2 O 3 are shown in Figure B. The peaks at 368.8 and 367.9 are assigned to Ag 0 and Ag + , respectively. – The obtained results (Table ) show that the fraction of Ag 0 and Ag + species exhibited almost no change upon exposure to N 2 O and a vacuum, indicating that the oxidation state of the Ag species remained unchanged during N 2 O decomposition.…”

Adjusting the Chemical Reactivity of Oxygen for Propylene Epoxidation on Silver by Rational Design: The Use of an Oxyanion and Cl

“…Thus, the lack of O elec may be a limitation in the direct epoxidation of propylene on silver, but this has yet to be proven. While increasing the concentration of O elec may improve propylene oxide selectivity, the nature of this species, and hence means of increasing its coverage, has been long debated. ,,− In early investigations it was postulated that a special form of adsorbed oxygen (O ads ) would selectively oxidize ethylene to EO. − In propylene oxidation, facile allylic hydrogen abstraction by O ads results in either complete combustion or acrolein formation . It was proposed that because propylene is a more effective reducing agent than ethylene, this would inhibit surface-to-subsurface transport of O atoms and the lower epoxide selectivity to PO would result from the weakly electrophilic O ads .…”