In Situ Observation of CO Oxidation on Ag(110)(2×1)-O by Scanning Tunneling Microscopy:  Structural Fluctuation and Catalytic Activity

Abstract

On the added-row reconstructed Ag(110)(nx1)-O surfaces where one-dimensional -Ag-O-Ag-O- chains arrange periodically, the clean-off reaction of O adatoms by CO was investigated using variable temperature scanning tunneling microscopy (VT-STM). Based on the in situ STM observations of the surface structure variation in the course of the reaction at various temperatures, we found that the reaction kinetics are significantly affected by the structural transition of AgO chains from a solid straight line configuration to dynamically fluctuating configurations. Below 230 K where the chains are straight, the reaction takes place only at the end of the chains, so that the reaction progresses in the zero-order kinetics with the reaction front propagating along the chain. The temperature dependence of the reaction rates yields the activation barrier of 41 kJ/mol and the preexponential factor of 1.7 x 10(3) cm(-2) s(-1). At room temperature, the reaction rate is drastically accelerated when almost half of the O adatoms are eliminated and the chains start fluctuating. The dynamic formation of active sites equivalent to the end of chains upon the chain fluctuation results in the nonlinear increase of the reaction rate.

The dissociation-induced displacement of chemisorbed O2 by mobile O atoms and the autocatalytic recombination of O due to chain fragmentation on Ag(110)

“…Normalization of the number of fragments observed in a (5x1) and (9x1) O/Ag(110) structure with the factor as obtained from the fit to the isothermal and TPD dataleads to a complete overlap of both curves (compare Fig. 4 in the work of Nakagoe et al [39] and Fig. 8 in this work).…”

“…It is well known that the chain-like structure of adsorbed fragments progressively as the coverage of oxygen adatoms decreases. [39] Prior studies of CO oxidation on Ag (110) reconstructed surface severely inhibited the reaction rate. [40] Both the isothermal desorption and temperature programmed desorption of oxygen above 520 K can be explained by this fragmentation of the added row structure.…”

“…provide fragmentation fractions for two (nx1) reconstructions as a function of temperature [39]. Normalization of the number of fragments observed in a (5x1) and (9x1) O/Ag(110) structure with the factor as obtained from the fit to the isothermal and TPD dataleads to a complete overlap of both curves (compare Fig.…”

Direct visualization of quasi-ordered oxygen chain structures on Au(110)-(1 × 2)

“…reaction rates. [45,46] Although, as discussed in the following, the exact chain structure is different, similar end effects could be expected on Au(110).…”

Explosive evolution of hydrogen abstraction of water on oxidized Ag(110) surfaces studied by scanning tunnelling microscopy

“…[8][9][10] The reactivity of O adatoms in the AgO chains depends on the location of oxygen, i.e., O at the end of the chain is highly more reactive than O at the middle of the chain. [11][12][13] This site-specific reactivity of O results in drastic acceleration of CO oxidation as the 1D chains start fluctuating. 12,13 Thus, the dynamically controlled reactivity of O in the 1D chains at Ag(110)(n  1)-O surfaces stimulates us to investigate how surface reactions with adsorbates other than CO evolve in time and space.…”