Direct visualization of defect-mediated dissociation of water on TiO2(110)

Bikondoa, Oier; Pang, Chi L.; Ithnin, R.; Muryn, Christopher A.; Ōnishi, Hiroshi; Thornton, G.

doi:10.1038/nmat1592

Cited by 596 publications

(747 citation statements)

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“…13 In addition, the terraces exhibit very few OH groups as a consequence of water dissociation from the residual gas. 13,35 The larger features correspond to Pt clusters. Their apparent size (height as well as width) clearly increases from Pt 3 to Pt 10 .…”

Section: ■ Resultsmentioning

confidence: 99%

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

et al. 2014

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We determined the CO oxidation rates for sizeselected Pt n (n ∈ {3,7,10}) clusters deposited onto TiO 2 (110). In addition, we investigated the cluster morphologies and their mean sizes before and after the reaction. While the clusters are fairly stable upon annealing in ultrahigh vacuum up to 600 K, increasing the temperature while adsorbing either one of the two reactants leads to ripening already from 430 K on. This coarsening is even more pronounced when both reactants are dosed simultaneously, i.e., running the CO oxidation reaction. Since the ripening depends on the size initially deposited, there is nevertheless a size effect; the catalytic activity decreases monotonically with increasing initial cluster size. ■ INTRODUCTIONIt is well established that small metal clusters have physical and chemical properties distinctively different from those of the bulk. While the properties change rather smoothly in the socalled scalable size regime, each additional atom can substantially change the properties of interest in the nonscalable size range. 1 Metal clusters of well-defined size, shape, and composition, supporting on metal oxide surfaces, provide model catalysts that offer a fundamental understanding of the processes taking place in real catalysts via structure−reactivity correlation at the molecular level. 2 This has been shown for the smallest clusters in numerous examples, three decades ago in the famous photographic experiment by Fayet et al., 3 and more recently in the work of Heiz et al. for metal clusters on MgO(100) 4−9 and of Anderson et al., 10,11 Watanabe et al.,12 and our group 13 for metal clusters on rutile TiO 2 (110). In all these examples, size-selected cluster deposition was employed in order to prepare monodispersed supported clusters which are difficult to obtain by conventional preparation methods. We note that experiments with a finite cluster size distribution also make it possible to study size effects in the scalable regime by varying the mean cluster size. 14 However, to firmly associate a catalytic property with a certain size, one has to probe the cluster morphology not only before but also after the reaction. This information is essentially lacking in most of the experiments cited above.It is fairly well accepted that metal catalysts deactivate, in particular under reaction conditions, as a consequence of morphological changes of the supported clusters, and that this change depends on the cluster size and cluster−support interaction. 2,15−24 This argument is even more important when the smallest entities, with only a handful of atoms, are under investigation. Accordingly, not only in model catalysts with well-defined initial conditions but also in real catalysts, this stability under the reaction conditions sets a clear limitation to the minimum cluster size that can be reasonably employed.Here we present a systematic study of the initial sizedependent reactivity and of the thermal as well as chemical stability of very small Pt clusters on rutile TiO 2 (110)-(1×1) in ...

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Section: ■ Resultsmentioning

confidence: 99%

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

et al. 2014

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“…There are evidences in the literature showing that oxide surfaces may be very sensitive to the traces of water in an ambient, even in the vacuum background [49,50].…”

Section: General Discussion and Proposed Mechanismmentioning

confidence: 99%

Monolayer iron oxide film on platinum promotes low temperature CO oxidation

Sun

Qin

Lewandowski

et al. 2009

Journal of Catalysis

224

236

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Abstract. CO oxidation on a clean Pt(111) single crystal and thin iron oxide films grown on Pt(111) was studied at different CO:O 2 ratios (between 1:5 and 5:1) and partial pressures up to 60 mbar at 400 -450 K. Structural characterization of the model catalysts was performed by scanning tunneling microscopy, low energy electron diffraction, Auger electron spectroscopy and temperature programmed desorption. It is found that monolayer FeO (111) films grown on Pt(111) are much more active than clean Pt(111) and nm-thick Fe 3 O 4 (111) films at all reaction conditions studied. Post-characterization of the catalysts revealed that at CO:O 2 >1 the FeO(111) film dewets the Pt surface with time, ultimately resulting in highly dispersed iron oxide particles on Pt(111). The film dewetting was monitored in situ by polarisation-modulated infrared reflection absorption spectroscopy. The reaction rate at 450 K exhibited first order for O 2 and non-monotonously depended on CO pressure. In O 2 -rich ambient the films were enriched with oxygen while maintaining the long range ordering.Based on the structure-reactivity relationships observed for the FeO/Pt films, we propose that the reaction proceeds through the formation of a well-ordered, oxygen-rich FeO x (1 < x < 2) film that reacts with CO through the redox mechanism. The reaction induced dewetting in fact deactivates the catalyst. The results may aid in our deeper understanding of reactivity of metal particles encapsulated by thin oxide films as a result of strong metal support interaction.

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“…[6][7][8] Water and methanol are respectively the reactant and sacrificial agent in the photocatalytic water reduction reaction catalyzed by TiO 2 , thus their individual adsorptions on various TiO 2 single crystals have been studied on TiO 2 single crystal surfaces using various techniques including scanning tunneling microscopy, thermal desorption spectra (TDS), X-ray photoelectron spectroscopy (XPS) and theoretical calculations. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Since water and methanol co-exist as the photocatalytic reactants, the competitive adsorption of water and methanol on TiO 2 surfaces must play an important role in the photocatalytic activity. However, only limited results have been reported on the competitive adsorption of water and methanol on TiO 2 single crystal surfaces.…”

Section: Introductionmentioning

confidence: 99%

Structural Dependence of Competitive Adsorption of Water and Methanol on TiO₂ Surfaces

et al. 2017

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Employing TiO 2 anatase (001)-(1×4), rutile (110) and rutile (011)-(2×1) single crystal surfaces, we comprehensively studied the effects of TiO 2 surface structures on the competitive adsorption of water and methanol by means of low energy electron diffraction, thermal desorption spectra and X-ray photoelectron spectroscopy. The relative adsorption strengths of chemisorbed methanol and water vary with the TiO 2 surface structures and the adsorption sites. This leads to TiO 2 surface structure-dependent competitive adsorption of water and methanol. The chemisorption of CH 3 OH on TiO 2 anatase (001)-(1×4) surface is seldom affected by pre-covered water at low coverages but is affected by pre-covered water at high coverages; the chemisorption of CH 3 OH on TiO 2 rutile (110) surface is seldom affected by pre-covered water; and the chemisorption of CH 3 OH on TiO 2 rutile (011)-(2×1) surface is affected by pre-covered water even at low coverages. These results deepen the fundamental understandings of surface chemistry on TiO 2 surfaces.

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Direct visualization of defect-mediated dissociation of water on TiO2(110)

Cited by 596 publications

References 29 publications

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

Monolayer iron oxide film on platinum promotes low temperature CO oxidation

Structural Dependence of Competitive Adsorption of Water and Methanol on TiO₂ Surfaces

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Direct visualization of defect-mediated dissociation of water on TiO2(110)

Cited by 596 publications

References 29 publications

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Ptn/TiO2(110)-(1×1)

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Ptn/TiO2(110)-(1×1)

Monolayer iron oxide film on platinum promotes low temperature CO oxidation

Structural Dependence of Competitive Adsorption of Water and Methanol on TiO2 Surfaces

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Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

Reaction-Induced Cluster Ripening and Initial Size-Dependent Reaction Rates for CO Oxidation on Pt_n/TiO₂(110)-(1×1)

Structural Dependence of Competitive Adsorption of Water and Methanol on TiO₂ Surfaces