The role of structural changes in the excitation of chemical waves in the system Rh(110)/NO+H2

Abstract

Previous investigations have demonstrated that the formation of chemical waves in the NO+H2 reaction on Rh(110) involves a cyclic transformation of the surface structure via various N,O-induced reconstructions, i.e., starting form the c(2×6)-O a cycle is initiated comprising the formation of a (2×3)/(3×1)-N and a mixed c(2×4)-2O,N structure. The stability and reactivity of these structures has been investigated in titration experiments as well as under stationary reaction conditions employing LEED, work function, rate measurements, and thermal desorption spectroscopy. It was shown that the c(2×6)-O and c(2×4)-2O,N structures exhibit a low reactivity whereas the (2×1)/(2×1)-N displays only a small to moderate decrease in catalytic activity (≈20%–30%) compared to the clean surface. On the basis of these results, an excitation mechanism for pulses in the NO+H2 reaction on Rh(110) was constructed consisting of the sequence c(2×6)-O, (2×1)/(3×1)-N c(2×4)-2O,N, c(2×6)-O.

Spectromicroscopy of pulses transporting alkali metal in a surface reaction

“…The two N 1s components can be assigned to two different nitrogen species: chemisorbed nitrogen in the (2 Â 1)-N phase and nitrogen coadsorbed with oxygen in the mixed c(2 Â 4)-2O,N phase. 18,24,25 In the literature, the N 1s binding energy for the (3 Â 1)-N phase on Rh(110) (similar to the (2 Â 1)-N phase) is reported to be 397.3 eV and the one corresponding to the mixed c(2 Â 4)-NO coadsorbate phase equals 397.6 eV. 27 The separation of 0.3 eV is exactly the one we observe in the experiment.…”

“…24,25 The only significant modification with respect to the original mechanism is that the pure oxygen phase, the c(2 Â 6)-O, has to be replaced as the resting state by a K + O coadsorbate phase. The modified excitation cycle comprises the following sequence: K + O-coadsorbate phase (resting state) -(2 Â 1)-N (excited state) -c(2 Â 4)-2O,N (refractory state) -K + O coadsorbate phase.…”

Excitability in the H2+O2 reaction on a Rh(110) surface induced by high coverages of coadsorbed potassium

“…2(a), look rather similar to the target patterns observed in the NO + H 2 reaction over both, unpromoted and K-promoted Rh(110) single crystal surfaces. [8][9][10]18 There are also a number of differences. In contrast to the NO + H 2 reaction, the present system exhibits a pronounced front instability as demonstrated by the PEEM images in Figs.…”

Imaging with Chemical Analysis: Adsorbed Structures Formed during Surface Chemical Reactions

“…[19,21] The complex chemistry of NO + H 2 reaction, involving the coexistence of O-(1 n) and N-(n 1) reconstructions of the substrate surface with different diffusion anisotropy, [17] leads to a large variety of chemical wave patterns, such as targets and spirals. [2,18,24] The velocity, shape and wavelength of the reaction-diffusion patterns can be influenced by modifying the structural and chemical properties of the catalyst surface, for example, by adding adatoms of another element we call here "modifier". [25] The "modifier" can steer the catalytic activity and/or selectivity or act as deactivator.…”

“…[24,[27][28][29] Alkali metals (AM) are a specific type of "modifier": they are very mobile on metal surfaces and have a very high chemical affinity to so-called electronegative adatoms such as O. [26] In the case of water formation reaction the travelling chemical waves still exist but the front profile and the front velocity are not constant but change continuously.…”