Observation of free hydroxyl groups on the surface of ultra thin ice layers on Ni(110)

doi:10.1016/0039-6028(92)90211-N

Surface Science

Volume 261, Issues 1–3, 15 January 1992, Pages L44-L48

https://doi.org/10.1016/0039-6028(92)90211-N Get rights and content

Abstract

Free (non hydrogen-bonded) O-D (O-H) groups at the surface of ice layers have been identified by infra red reflection-absorption spectroscopy through their high frequency, narrow bandwidth and behaviour upon condensation of H₂O (D₂O) ice on top of the D₂O (H₂O) ice. The enhancement of the absorption coefficient of the OD stretch upon formation of hydrogen bonds in D₂O ice layers on Ni(110) is found to lie between 30 and 36 compared to “free” O-D groups.

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Electronic effects on the water adsorption behaviour and structure formation on pseudomorphic Pt films on Ru(0001)
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This was described in detail in excellent reviews by Thiel and Madey [1], Henderson [2], Hodgson and Haq [3], and Carrasco et al. [4]. The interaction of water with chemically active surfaces such as Ni or Al surfaces was investigated in detail by Norton and coworkers [5–12]. Much less is known, however, when increasing the complexity of the system, e.g., by going to bimetallic surfaces or including coadsorbed species [13–18].
Aiming at a fundamental understanding of the interaction of water with bimetallic electrode surfaces, we have systematically investigated the adsorption behaviour and structure formation of water on structurally well-defined Pt/Ru(0001) surfaces under ultrahigh vacuum (UHV) conditions by scanning tunnelling microscopy (STM). For surfaces consisting of pseudomorphic Pt films with thicknesses between 1 and 4 atomic layers on a Ru(0001) substrate, we find a systematic variation of the adsorbate coverage and structure with increasing thickness of the Pt film, from relatively mobile monomers and dimers over stable hexamers to a contiguous hexagonal adlayer for identical exposures, where the latter structures are suggested to represent different stages of a nucleation and growth process leading to a closed water adlayer on these Pt/Ru(0001) surfaces. The structure of the water adlayer differs significantly from previously reported structures of water monolayers on Pt(111). The results are discussed making use of trends in the adsorption behaviour of similar Pt/Ru(0001) surfaces established in previous experimental and theoretical studies.
Insight into the suppressive effects of sulphoxy species on the NO-D <inf>2</inf> reaction on platinum surfaces: A surface science approach
2011, Surface Science
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Special attention is paid to clarifying: (1) how oxidation of SO2 proceeds on a stepped Pt surface; (2) how adsorption of NO molecules on a stepped Pt surface is affected by surface sulphoxy species that result from the reaction between SO2 and O2 at various temperatures; (3) how the efficiency of NO–H (H2 is dissociatively adsorbed on Pt surfaces) reaction is changed in the presence of SO2 or surface sulphoxy species; and consequently, (4) providing an explanation for the O2 induced mitigation of SO2 poisoning effects on the NO–H2 reaction. All the experiments were carried out in a standard UHV system described elsewhere [10,11]. Briefly, a stainless steel UHV chamber is pumped by a turbo-molecular pump, which is in turn backed by an oil diffusion pump.
The influence of S¹⁸O₂, O₂ and their reaction products, surface sulphoxy species, on NO–D₂ reactions on the surface of stepped Pt(332) was studied. Oxidation of S¹⁸O₂ by O₂ proceeds to a very slight extent on Pt(332), taking place as the surface temperature is increased to 300 K and higher. The oxidation reaction gives rise to surface sulphoxy species (S¹⁸O_x, x > 2) that persist on the surface up to 500 K but desorb completely at 600 K. The surface sulphoxy species desorb mainly as S¹⁸O₂ (predominantly) and S¹⁸O₃. On the other hand, co-adsorbed S¹⁸O₂ molecules render the desorption of O atoms, (which otherwise occurs at 700 K and higher from a clean Pt(332) surface), undetectable. Such oxygen desorption reappears and gains a considerable intensity as the sulphoxy species covered Pt(332) surface was further exposed to NO molecules. However, NO dissociation is suppressed in the presence of S¹⁸O₂, O atoms and surface sulphoxy species; the suppressive effect from O atoms and surface sulphoxy species is much more significant than that from S¹⁸O₂. No N₂ desorption resulting from NO dissociation is detected under some conditions.
The suppressive effect exerted by O atoms and surface sulphoxy species also holds for the NO–D reaction, but is highly dependent on the exposures of O₂ and S¹⁸O₂. The NO–D reaction is not suppressed on the Pt(332) surface which has been pre-exposed to 0.4 L O₂ at 90 K and then annealed to 200 K, due to rapid removal of O atoms (including those from NO dissociation) as a result of the facile reaction between O and D. On the Pt(332) surface, pre-exposed to O₂ and S¹⁸O₂ and then annealed to 400 K, the efficiency of the NO–D reaction (manifested by N₂ production) is obviously lower than that on a clean surface (without surface sulphoxy species); however, the suppressive effect becomes significant only as the exposures of O₂ and S¹⁸O₂ are ≥ 0.4 L.
Surface sulphoxy species-induced suppression of the NO–D reaction on Pt(332) mainly results from NO–Pt interactions being weakened and a lack of D atom supply at the surface temperatures where NO dissociation becomes significant. D₂ desorption from the Pt(332) surface finishes at ~ 350 K, at which temperature surface sulphoxy species and O atoms persist and NO dissociation just becomes appreciable. As such, the NO–D reaction evolves into NO dissociation on the surface sulphoxy species covered Pt(332).
The present results also suggest that the site blocking effect of surface sulphoxy species and O atoms does not evidently contribute to their suppression of NO–D reaction.
NO dissociation and N<inf>2</inf> production in the presence of co-adsorbed S<sup>18</sup>O<inf>2</inf> and D<inf>2</inf> on Pt(3 3 2)
2009, Surface Science
NO dissociation and subsequent N₂ production in the presence of co-adsorbed S¹⁸O₂ and D₂ on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Reduction of NO by D (D₂ is adsorbed dissociatively on Pt surfaces) proceeds to a limited extent, because this reaction is rate-controlled by NO dissociation and the supply of D atoms at the higher surface temperatures at which NO dissociation becomes significant (350 K and higher). NO–D reaction is suppressed in the presence of S¹⁸O₂, depending significantly on the S¹⁸O₂ coverage and the competition between the reactions NO–D and S¹⁸O₂–D. When the supply of D₂ is limited, e.g., 0.1 L in this study, the presence of S¹⁸O₂ suppresses the NO–D reaction. With a sufficient supply of D₂, e.g., 0.4 L and higher, D-atom competing reactions do not play a role any more because the reactions of both NO and S¹⁸O₂ with D proceed only to a very limited extent. As such, generation of O atoms from S¹⁸O₂ dissociation is the main reaction that leads to the suppression in NO dissociation and consequently, N₂ production.
It is also concluded that the presence of S¹⁸O₂ does not seriously poison the active sites on the Pt surface, providing that there is a sufficient D supply to remove O atoms from both NO dissociation and S¹⁸O₂ dissociation.
Interactions between S<sup>18</sup>O<inf>2</inf> and NO on the surface of stepped Pt(3 3 2)
2009, Surface Science
Interactions between S¹⁸O₂ and NO on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Adsorbed S¹⁸O₂ does not seem to have a preference for step sites on Pt(3 3 2). As such, the presence of S¹⁸O₂ molecules following exposures of ⩽1.6 L does not significantly block the subsequent adsorption of NO (⩽0.8 L) on these step sites. Adsorbed S¹⁸O₂ molecules undergo dissociation (S¹⁸O₂(a) → S¹⁸O(a) + ¹⁸O(a)) as the surface temperature is increased to 250 K and above, but the resultant ¹⁸O(a) further reacts with sulfur oxides (S¹⁸O₂(a) and S¹⁸O(a)) to form S¹⁸O_x (x > 2) species at ∼400 K and above. The S¹⁸O_x species desorb as S¹⁸O₂. Even though the presence of co-adsorbed S¹⁸O₂ suppresses NO dissociation and subsequent N₂ production, this effect is not significantly enhanced with increasing the exposures of S¹⁸O₂ in the range ⩽1.6 L; N₂ desorption is still detectable at an exposure of 1.6 L S¹⁸O₂, at which a considerable amount of S¹⁸O₂ desorption is detected.
Catalytic reduction of NO in the presence of benzene on a Pt(3 3 2) surface
2008, Applied Surface Science
The catalytic reduction of NO in the presence of benzene on the surface of Pt(3 3 2) has been studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). IR spectra show that while the presence of benzene molecules at low coverage (e.g., following an exposure of just 0.25 L) promotes NO–Pt interaction, the adsorption of NO on Pt(3 3 2) at higher benzene coverages is suppressed. It is also shown that there are no strong interactions between the adsorbed NO molecules and the benzene itself or benzene-derived hydrocarbons, which can lead to the formation of intermediate species that are essential for N₂ production.
TDS results show that the adsorbed benzene molecules undergo dehydrogenation accompanied by hydrogen desorption starting at 300 K and achieving a maximum at 394 K. Subsequent dehydrogenation of the benzene-derived hydrocarbons then begins with hydrogen desorption starting at 500 K. N₂ desorption from NO adlayers on clean Pt(3 3 2) surface becomes significant at temperatures higher than 400 K, giving rise to a peak at 465 K. This peak corresponds to N₂ desorption from NO dissociation on step sites. The presence of benzene promotes N₂ desorption, depending on the benzene coverage. When the benzene exposure is 0.25 L, the N₂ desorption peak at 459 K is dramatically increased. Increasing benzene coverage also results in the intensification of N₂ desorption at ∼410 K. At benzene exposures of 2.4 L, N₂ desorption develops as a broad peak with a maximum at ∼439 K.
It is concluded that the catalytic reduction of NO by platinum in the presence of benzene proceeds by NO decomposition and subsequent oxygen removal at temperatures lower than 500 K, and NO dissociation is a rate-limiting step. The contribution of benzene to N₂ desorption is mainly attributed to providing a source of H, which quickly reacts with NO-derived atomic O, leaving the surface with more vacant sites for further NO dissociation.
NO-methanol interaction on the surface of Pt(3 3 2)
2007, Surface Science
The interaction between NO and CH₃OH on the surface of stepped Pt(3 3 2) was investigated using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). At 90 K, pre-dosed CH₃OH molecules preferentially adsorb on step sites, suppressing the adsorption of NO molecules on the same sites. However, due to a much stronger interaction with Pt, at 150 K and higher, the adsorption of NO molecules on step sites is restored, giving rise to peaks closely resembling those of NO molecules adsorbed on clean Pt(3 3 2) surface. Adsorbed CH₃OH is very reactive on this surface, and is readily oxidized to formate in the presence of O₂, even at 150 K. In contrast, reactions between CH₃OH and co-adsorbed NO are slight to non-existent. There are no new peaks in association with intermediates resulting from CH₃OH–NO interactions. It is concluded that the reduction of NO with CH₃OH on Pt(3 3 2) does not proceed through a mechanism of forming intermediates.

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Surface science lettersObservation of free hydroxyl groups on the surface of ultra thin ice layers on Ni(110)

Abstract

Surf. Sci. Rep.

Surf. Sci.

Surf. Sci.

Surf. Sci.

Spectrochim. Acta

Surface science letters
Observation of free hydroxyl groups on the surface of ultra thin ice layers on Ni(110)