NOx storage in model Pt/Ba NSR catalysts: fabrication and reactivity of BaO nanoparticles on Pt(111)

Stone, Peter; Ishii, Masataka; Bowker, Michael

doi:10.1016/s0039-6028(03)00614-9

Cited by 40 publications

(44 citation statements)

References 27 publications

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“…10 It was also reported that whereas the nitrite formation is a rapid process, conversion of nitrites into nitrates occurs at a slower pace. 10 Formation of BaO 2 was also reported by XPS 8,10 and STM 11,12 in similar model catalyst studies. BaO 2 is a relatively stable peroxide in its bulk form, releasing oxygen at T > 800 K and fully decomposing at T > 1200 K. 13 It was suggested that in NSR applications BaO 2 formation plays an important role in the Ba(NO 3 ) 2 decomposition, where BaO 2 species generated during the nitrate decomposition exist on the surface even after the complete desorption of all of the nitrates.…”

Section: Introductionsupporting

confidence: 67%

Role of the Exposed Pt Active Sites and BaO₂ Formation in NO_x Storage Reduction Systems: A Model Catalyst Study on BaO_x/Pt(111)

et al. 2011

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ABSTRACT:BaO x (0.5 MLE -10 MLE)/Pt(111) (MLE: monolayer equivalent) surfaces were synthesized as model NO x storage reduction (NSR) catalysts. Chemical structure, surface morphology, and the nature of the adsorbed species on BaO x /Pt(111) surfaces were studied via X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). For θ BaOx < 1 MLE, (2 Â 2) or (1 Â 2) ordered overlayer structures were observed on Pt(111), whereas BaO(110) surface termination was detected for θ BaOx = 1.5 MLE. Thicker films (θ BaOx g 2.5 MLE) were found to be amorphous. Extensive NO 2 adsorption on BaO x (10 MLE)/Pt(111) yields predominantly nitrate species that decompose at higher temperatures through the formation of nitrites. Nitrate decomposition occurs on BaO x (10 MLE)/Pt(111) in two successive steps: (1) NO(g) evolution and BaO 2 formation at 650 K and (2) NO(g) + O 2 (g) evolution at 700 K. O 2 (g) treatment of the BaO x (10 MLE)/ Pt(111) surface at 873 K facilitates the BaO 2 formation and results in the agglomeration of BaO x domains leading to the generation of exposed Pt(111) surface sites. BaO 2 formed on BaO x (10 MLE)/Pt(111) is stable even after annealing at 1073 K, whereas on thinner films (θ BaOx = 2.5 MLE), BaO 2 partially decomposes into BaO, indicating that small BaO 2 clusters in close proximity of the exposed Pt(111) sites are prone to decomposition. Nitrate decomposition temperature decreases monotonically from 550 to 375 K with decreasing BaO x coverage within θ BaOx = 0.5 to 1.0 MLE. Nitrate decomposition occurs at a rather constant temperature range of 650À700 K for thicker BaO x overlayers (2.5 MLE < θ BaOx < 10 MLE). These two distinctly characteristic BaO x -coveragedependent nitrate decomposition regimes are in very good agreement with the observation of the so-called "surface" and "bulk" barium nitrates previously reported for realistic NSR catalysts, clearly demonstrating the strong dependence of the nitrate thermal stability on the NO x storage domain size.

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Section: Introductionsupporting

confidence: 67%

Role of the Exposed Pt Active Sites and BaO₂ Formation in NO_x Storage Reduction Systems: A Model Catalyst Study on BaO_x/Pt(111)

et al. 2011

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“…Figure 1a and 2 shows two images obtained after the adsorption of Ba, followed by oxidation under different conditions. In Figure 1a we believe we have formed the BaO(111) surface [9], whereas in figure 1b we propose that BaO 2 is formed [10]. The reason for these assignments is that the structure in 1a) is thermally stable, and the atomic spacing corresponds with that expected for the BaO(111) surface with a (2 · 2) reconstruction.…”

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confidence: 84%

NSR Catalysis studied using Scanning Tunnelling Microscopy

et al. 2007

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In this paper we report the fabrication of model catalysts prepared to understand the structure of the BaO surface. This utilises the 'inverse' catalyst method, that is, the oxide layer is fabricated onto the top of a metal single crystal surface. We show that we can atomically resolve the surface structure of BaO(111) and that it presents a (2·2) reconstruction at its surface. Under other dosing conditions we can produce a layer which is metastable at 573K, which we believe to be the peroxide, BaO 2 . We have shown that the BaO layer can store NO x from a mix of NO and oxygen, even under the extremely low exposure conditions of UHV, proving that the NOx storage process is a facile one. The results indicate that it is not necessary to have NO2 in the gas phase in order to store NO x .KEY WORDS: NSR; NOx storage and reduction; SCR; STM; model catalysts; BaO model catalysts.NSR (NOx storage and reduction) catalysis is an important strategy to aid in the removal of pollutants from lean-burn type engines [1,2]. There is a considerable amount of work relating to this process in reactors and from infra-red measurements [3,4], but little which is devoted to the resolution of these processes at the ultra-nanoscale. To that end we here report on the first studies related to NSR using STM.Our STM has been described in detail elsewhere [5], but for brevity, suffice it to say that it has the capability of achieving atomic resolution, but also a near-unique capability of imaging at high temperature (up to 1000K), with relatively little thermal drift. It also has facilities for surface analysis (Auger electron spectroscopy) and surface cleaning, sputtering and gas treatment. All of the work below was carried out under ultrahigh vacuum conditions to ensure the purity of the surfaces studied and of the gases dosed.The strategy here is to attempt to make inverse model catalysts by depositing BaO onto the surface of Pt(111). The reason for using this strategy is that STM relies on having conductivity in the imaged material in order to obtain a tunnelling current. It has been shown that thin layers of wide band gap materials (even alumina [6,7]) are suitable for imaging, provided they are fabricated onto conducting support materials, usually single crystal metals [8]. Figure 1a and 2 shows two images obtained after the adsorption of Ba, followed by oxidation under different conditions. In Figure 1a we believe we have formed the BaO(111) surface [9], whereas in figure 1b we propose that BaO 2 is formed [10]. The reason for these assignments is that the structure in 1a) is thermally stable, and the atomic spacing corresponds with that expected for the BaO(111) surface with a (2 · 2) reconstruction. Note that the (111) BaO-(1 · 1) surface is polar and unstable and is therefore not expected to form, whereas theory predicts a (2 · 2) reconstruction for this surface, producing a near-neutral layer with low surface energy, figure 1b [9]. Other structures are identified under varying oxygen treatment conditions, which may be further recon...

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“…[16,[25][26][27][28][29][30][31]] Surprisingly, there have been very few attempts to translate the NSR concept to a tractable model approach. Pioneering work on the interaction of NO 2 with model BaO surfaces was published by Bowker and co-workers, [16,32,33] Szanyi and co-workers [23,[34][35][36][37] and recently by us. [18,[38][39][40] Here we present the first model study on a "complete" NSR model system, involving the Ba storage compound and co-deposited noble metal nanoparticles on an alumina model support.…”

Section: Introductionmentioning

confidence: 98%

Interaction of NO₂ with Model NSR Catalysts: Metal–Oxide Interaction Controls Initial NO_x Storage Mechanism

et al. 2008

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Using scanning tunneling microscopy (STM), molecular-beam (MB) methods and time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we investigate the mechanism of initial NO(x) uptake on a model nitrogen storage and reduction (NSR) catalyst. The model system is prepared by co-deposition of Pd metal particles and Ba-containing oxide particles onto an ordered alumina film on NiAl(110). We show that the metal-oxide interaction between the active noble metal particles and the NO(x) storage compound in NSR model catalysts plays an important role in the reaction mechanism. We suggest that strong interaction facilitates reverse spillover of activated oxygen species from the NO(x) storage compound to the metal. This process leads to partial oxidation of the metal nanoparticles and simultaneous stabilization of the surface nitrite intermediate.

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NOx storage in model Pt/Ba NSR catalysts: fabrication and reactivity of BaO nanoparticles on Pt(111)

Cited by 40 publications

References 27 publications

Role of the Exposed Pt Active Sites and BaO₂ Formation in NO_x Storage Reduction Systems: A Model Catalyst Study on BaO_x/Pt(111)

Role of the Exposed Pt Active Sites and BaO₂ Formation in NO_x Storage Reduction Systems: A Model Catalyst Study on BaO_x/Pt(111)

NSR Catalysis studied using Scanning Tunnelling Microscopy

Interaction of NO₂ with Model NSR Catalysts: Metal–Oxide Interaction Controls Initial NO_x Storage Mechanism

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NOx storage in model Pt/Ba NSR catalysts: fabrication and reactivity of BaO nanoparticles on Pt(111)

Cited by 40 publications

References 27 publications

Role of the Exposed Pt Active Sites and BaO2 Formation in NOx Storage Reduction Systems: A Model Catalyst Study on BaOx/Pt(111)

Role of the Exposed Pt Active Sites and BaO2 Formation in NOx Storage Reduction Systems: A Model Catalyst Study on BaOx/Pt(111)

NSR Catalysis studied using Scanning Tunnelling Microscopy

Interaction of NO2 with Model NSR Catalysts: Metal–Oxide Interaction Controls Initial NOx Storage Mechanism

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Role of the Exposed Pt Active Sites and BaO₂ Formation in NO_x Storage Reduction Systems: A Model Catalyst Study on BaO_x/Pt(111)

Role of the Exposed Pt Active Sites and BaO₂ Formation in NO_x Storage Reduction Systems: A Model Catalyst Study on BaO_x/Pt(111)

Interaction of NO₂ with Model NSR Catalysts: Metal–Oxide Interaction Controls Initial NO_x Storage Mechanism