Dynamics of ultrathin V-oxide layers on Rh(111) in catalytic oxidation of ammonia and CO

Boehn, Bernhard von; Preiss, A.; Imbihl, R.

doi:10.1039/c6cp03637f

Cited by 13 publications

(26 citation statements)

References 26 publications

(74 reference statements)

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“…In catalytic methanol oxidation the system VO x /Rh(111) exhibited a high catalytic activity and displayed remarkable dynamic behavior [25,31], whereas VO x /Pt(111) showed negligible catalytic activity and practically no dynamics at all. In this comparison we refer to submonolayer coverages of VO x and reaction conditions in the 10 −4 mbar range.…”

Section: Catalytic Activity Of Vo X /Pt(111)mentioning

confidence: 99%

“…A natural question was how general the phenomenon of a reaction-induced island coalescence is, i.e., whether such ripening processes can also be observed in other reactions [27], with different support materials [28][29][30], and with other oxidic catalysts. It turned out that a number of oxidation reactions showed qualitatively the same behavior on VO x /Rh(111) as long as O 2 is used as oxidizing agent [31].…”

Section: Introductionmentioning

confidence: 96%

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Reactivity and Stability of Ultrathin VOx Films on Pt(111) in Catalytic Methanol Oxidation

2020

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The growth of ultrathin layers of VOx (< 12 monolayers) on Pt(111) and the activity of these layers in catalytic methanol oxidation at 10−4 mbar have been studied with low-energy electron diffraction, Auger electron spectroscopy, rate measurements, and with photoemission electron microscopy. Reactive deposition of V in O2 at 670 K obeys a Stranski–Krastanov growth mode with a (√3 × √3)R30° structure representing the limiting case for epitaxial growth of 3D-VOx. The activity of VOx/Pt(111) in catalytic methanol oxidation is very low and no redistribution dynamics is observed lifting the initial spatial homogeneity of the VOx layer. Under reaction conditions, part of the surface vanadium diffuses into the Pt subsurface region. Exposure to O2 causes part of the V to diffuse back to the surface, but only up to one monolayer of VOx can be stabilized in this way at 10−4 mbar.

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Section: Catalytic Activity Of Vo X /Pt(111)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Reactivity and Stability of Ultrathin VOx Films on Pt(111) in Catalytic Methanol Oxidation

2020

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“…One of the first questions that were asked after catalytic methanol oxidation exhibited quite remarkable reaction dynamics on VO x /Rh(111), was how general the island coalescence mechanism is. Experiments in which methanol oxidation was replaced by the H 2 + O 2 reaction, the NH 3 + O 2 reaction, and catalytic CO oxidation on VO x /Rh(111) showed in fact qualitatively the same behavior as in catalytic methanol oxidation (von Boehn et al, 2016). However, all these reactions have in common that O 2 is used as oxidizing agent.…”

Section: Oxidation With Nomentioning

confidence: 76%

“…What does not fit into the concept of reactive phase separation in the present case is that the coarsening does not approach a finite value. A control experiment in which V-oxide on Rh(111) was annealed in O 2 only, revealed that also in this case VO x islands of macroscopic size are formed (von Boehn et al, 2016). The condensation of VO x into stripes and circular islands under reaction conditions therefore appears to be driven by thermodynamics.…”

Section: Choice Of Model System and Methods Of Investigationmentioning

confidence: 93%

“…The formation of a VO x stripe pattern followed by a transition into a spot pattern of VO x islands is observed in a number of different chemical reactions on VO x /Rh(111), including the oxidation of H 2 , CO and ammonia (Lovis and Imbihl, 2011;von Boehn et al, 2016). Figure 3A shows the coarsening of a VO x stripe pattern under constant reaction condition on VO x /Rh(111) during the H 2 + O 2 reaction at 773 K. The pattern is the result of V and O forming a dense VO x coadsorbate phase.…”

Section: Choice Of Model System and Methods Of Investigationmentioning

confidence: 99%

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Dynamics of Ultrathin Vanadium Oxide Layers on Rh(111) and Rh(110) Surfaces During Catalytic Reactions

Boehn

Imbihl

2020

Front. Chem.

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Over the past 35 years rate oscillations and chemical wave patterns have been extensively studied on metal surfaces, while little is known about the dynamics of catalytic oxide surfaces under reaction conditions. Here we report on the behavior of ultrathin V oxide layers epitaxially grown on Rh(111) and Rh(110) single crystal surfaces during catalytic methanol oxidation. We use photoemission electron microscopy and low-energy electron microscopy to study the surface dynamics in the 10 −6 to 10 −2 mbar range. On VO x /Rh(111) we find a ripening mechanism in which VO x islands of macroscopic size move toward each other and coalesce under reaction conditions. A polymerization/depolymerization mechanism of VO x that is sensitive to gradients in the oxygen coverage explains this behavior. The existence of a substructure in VO x islands gives rise to an instability, in which a VO x island shrinks and expands around a critical radius in an oscillatory manner. At 10 −2 mbar the VO x islands are no longer stable but they disintegrate, leading to turbulent redistribution dynamics of VO x. On the more open and thermodynamically less stable Rh(110) surface the behavior of VO x is much more complex than on Rh(111), as V can also populate subsurface sites. At low V coverage, one finds traveling interface pulses in the bistable range. A state-dependent anisotropy of the surface is presumably responsible for intriguing chemical wave patterns: wave fragments traveling along certain crystallographic directions, and coexisting different front geometries in the range of dynamic bistability. Annealing to 1000 K causes the formation of macroscopic VO x islands. Under more reducing conditions dendritic growth of a VO x overlayer is observed.

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In situ Low‐Energy Electron Microscopy of Chemical Waves on a Composite V‐oxide/Rh(110) Surface

von Boehn,

Krisponeit,

Falta

et al. 2024

ChemPhysChem

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Chemical wave patterns and V‐oxide redistribution in catalytic methanol oxidation on a VOx/Rh(110) surface have been investigated in the 10‐4 mbar range with low‐energy electron microscopy (LEEM) and micro spot low‐energy electron diffraction (micro‐LEED) as in situ methods. V coverages of θV = 0.2 and 0.4 MLE (monolayer equivalents) were studied. Pulses display a c(2⨯2) pattern in the reduced part and (1⨯2) and c(2⨯8) structures in the oxidized part of the surface. At θV = 0.4 MLE (1⨯2) / (1⨯4) patterns with streaks along the [001] direction at the 1/8 positions are present on the oxidized part of the surface. This phase can be assigned to V‐oxide. Annealing the surface to 990 K under reaction conditions results in a macroscopic hole pattern in which holes of low VOx coverage are surrounded by a V‐oxide layer. Chemical waves propagate inside the holes as well as on the VOx covered parts of the surface.

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Dynamics of ultrathin V-oxide layers on Rh(111) in catalytic oxidation of ammonia and CO

Abstract: Catalytic oxidation of ammonia and CO has been studied in the 10 À4 mbar range using a catalyst prepared by depositing ultra-thin vanadium oxide layers on Rh (111)

Cited by 13 publications

References 26 publications

Reactivity and Stability of Ultrathin VOx Films on Pt(111) in Catalytic Methanol Oxidation

Reactivity and Stability of Ultrathin VOx Films on Pt(111) in Catalytic Methanol Oxidation

Dynamics of Ultrathin Vanadium Oxide Layers on Rh(111) and Rh(110) Surfaces During Catalytic Reactions

In situ Low‐Energy Electron Microscopy of Chemical Waves on a Composite V‐oxide/Rh(110) Surface

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