Model NSR catalysts: Fabrication and reactivity of barium oxide layers on Cu(111)

Tsami, A.; Grillo, Federico; Bowker, Michael; Nix, Roger M.

doi:10.1016/j.susc.2006.06.029

Cited by 45 publications

(114 citation statements)

References 36 publications

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“…It is worth mentioning that TPD spectra acquired after lower CO 2 exposures (e.g., 900 L) also result in an integrated CO 2 desorption signal whose magnitude is close to that of Figure 2a, indicating the complete saturation of the surface upon 1800 L CO 2 exposure. The temperature of the CO 2 desorption peak in Figure 2a is in good agreement with data published by A. Tsami et al, 20 where they have observed a CO 2 desorption peak at 773 K on the BaO/ Cu(111) surface. Mudiyanselage et al 21 observed two different CO 2 desorption features for the BaO/Pt(111) surface, a main peak at 748 K and a less intense second peak at 825 K. The main desorption peak at 748 K has been associated with the thermal decomposition of bulk-like barium carbonate species and the 825 K peak has been attributed to the decomposition of surface carbonate species.…”

Section: ■ Experimental Sectionsupporting

confidence: 91%

“…20,21 Therefore, in order to confirm that a clean BaO x overlayer can readily interact with CO 2 , we performed XPS analysis of a CO 2 -saturated thick BaO x overlayer, which demonstrated a typical C1s peak at 289.5 eV (data not shown) and an O1s shoulder at 531.5 eV, in agreement with the corresponding values reported for BaCO 3 . 20 TPD spectra associated with the exposure of a thick BaO x overlayer to 1800 L (10 −6 Torr ×30 min) CO 2 at 323 K are presented in Figure 2a. Carbonate species, which are formed upon CO 2 adsorption, decompose by yielding a strong CO 2 (m/z = 44) desorption peak at 780 K. This particular CO 2 desorption signal is also accompanied by a CO (m/z = 28) desorption signal (due to the fragmentation of CO 2 in the ionizer section of QMS), which is also located at 780 K with a line shape that is similar to that of CO 2 .…”

Section: ■ Experimental Sectionsupporting

confidence: 84%

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Interactive Surface Chemistry of CO₂ and NO₂ on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

et al. 2013

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Interactive surface chemistry of CO 2 and NO 2 on BaO x /Pt(111) model catalyst surfaces were investigated via X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques with a particular emphasis on the competition between different adsorbates for the catalytic adsorption sites and adsorbateinduced morphological changes. After NO 2 adsorption, nitrated BaO x /Pt(111) surfaces do not reveal available adsorption sites for CO 2 at 323 K, irrespective of the presence/absence of exposed Pt sites on the surface. Although NO 2 adsorption on thick BaO x (>10MLE)/ Pt(111) overlayers at 323 K leads to the formation of predominantly nitrate species, NO 2 adsorption on the corresponding carbonated surface leads to the formation of coexisting nitrates and nitrites. The presence of carbonates on BaO x /Pt(111) overlayers does not prevent NO 2 uptake. Carbonated BaO x (1.5 MLE)/Pt(111) surfaces (with exposed Pt sites) obtained via CO 2 adsorption can also further interact with NO 2 , forming surface nitrate/nitrite species, accompanied by the transformation of surface carbonates into bulk carbonate species. These results suggest that the nitrate formation process requires the presence of two adjacent unoccupied adsorption sites. It is apparent that in the presence of both NO 2 and CO 2 , carbonate species formed on Lewis base (O 2− ) sites enable the formation of nitrites on Lewis acid (Ba 2+ ) sites. Thermal aging, nitration, and carbonation have a direct impact on the morphology of the two-/three-dimensional (2D/3D) BaO x aggregates on Pt(111). While thermal aging in vacuum leads to the sintering of the BaO x domains, nitration and carbonation results in redispersion and spreading of the BaO x domains on the Pt(111) substrate. ■ INTRODUCTIONMost of the heterogeneous catalytic reactions rely on the consecutive or simultaneous adsorption of reactants on the catalytically active sites for the generation of products. Along these lines, it is not uncommon for reactants, intermediates, and/or products bearing similar chemical structures to compete for similar catalytically active adsorption sites in heterogeneous catalytic processes. Thus, molecular level understanding of the competition phenomena occurring during the adsorption of reactants/intermediates/products on surfaces is a fundamentally crucial aspect for the elucidation of heterogeneous catalytic reaction mechanisms. Automotive exhaust emission catalysts are not an exception to this subject, where multiple catalytic pathways proceed in a parallel fashion in the presence of a large variety of reactants/intermediates/products. For instance, during the operation of the NO x storage-reduction (NSR) catalysts, 1,2 oxygen-rich exhaust gases of lean burn engines are treated in two different alternating operational cycles called lean (abundant in oxygen) and rich (abundant in hydrocarbon) cycles, where toxic NO x gases are initially oxidized/trapped in the solid state and then successively reduced to harmless N 2 .Despite considerable...

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Section: ■ Experimental Sectionsupporting

confidence: 91%

Section: ■ Experimental Sectionsupporting

confidence: 84%

Interactive Surface Chemistry of CO₂ and NO₂ on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

et al. 2013

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“…For instance, the formation of a BaO (100) overlayer structure was observed on Cu (111) using LEED. 18 BaO (100) surface plane of bulk BaO unit cell has the lowest surface free energy compared with other surface facets. 20 Therefore, the formation of the BaO(100) surface is not surprising when the support has limited influence on the BaO overlayer due to an epitaxial mismatch leading to a weak interaction between the substrate and the overlayer.…”

Section: Methodsmentioning

confidence: 99%

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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“…Bowker and coworkers performed experiments on BaO films on PtA C H T U N G T R E N N U N G (111) and CuA C H T U N G T R E N N U N G (111) substrates, using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), IRAS and temperature-programmed desorption (TPD) spectroscopy. [13][14][15] Ozensoy et al studied the reaction of NO 2 on BaO/Al 2 O 3 / NiAlA C H T U N G T R E N N U N G (100), using the ultrathin Al 2 O 3 film on NiAlA C H T U N G T R E N N U N G (100). [16][17][18][19][20] More recently, the reaction of NO 2 with BaO deposits on Al 2 O 3 / NiAlA C H T U N G T R E N N U N G (110) were studied by Szanyi et al [21][22][23][24] and our group.…”

Section: Introductionmentioning

confidence: 99%

Model NO_x Storage Materials at Realistic NO₂ Pressures

Desikusumastuti¹,

Schernich²,

Happel³

et al. 2009

ChemCatChem

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The interaction of NO2 with single‐crystal‐based model NOx storage materials, consisting of barium aluminate nanoparticles on Al2O3/NiAl(110), are investigated by time‐resolved infrared reflection absorption spectroscopy (TR‐IRAS) at realistic NO2 partial pressures up to 1.75 mbar. The data is compared to spectra obtained under ultrahigh vacuum (UHV) conditions on the same model system. At 300 K, the NO2 uptake at pressures around 1 mbar proceeds through rapid initial formation of surface nitrites and nitrates, similar to that under UHV conditions. The vibrational spectra of the surface species formed at realistic NO2 pressures are comparable to those for species formed under UHV conditions. Beyond the formation of surface species, the formation of bulk nitrates occurs, but is kinetically strongly hindered. At a very low rate, the formation of a disordered barium bulk nitrate is detected. At 500 K, this kinetic hindrance is overcome and the available Ba2+ is quantitatively converted to bulk Ba(NO3)2. The IRAS spectrum of these Ba(NO3)2 particles differs characteristically from those obtained for nitrate multilayers formed upon incomplete conversion under UHV conditions. In addition to the formation of bulk Ba(NO3)2, a more weakly bound disordered nitrate species is formed. This species gives rise to a dynamic NO2 uptake and release well below the decomposition temperature of bulk Ba(NO3)2. The experiments show that model studies under UHV conditions mainly provide information on the initial reaction mechanism, whereas the observation of actual bulk NOx storage phases requires experiments at realistic temperatures and pressures.

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Model NSR catalysts: Fabrication and reactivity of barium oxide layers on Cu(111)

Cited by 45 publications

References 36 publications

Interactive Surface Chemistry of CO₂ and NO₂ on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

Interactive Surface Chemistry of CO₂ and NO₂ on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

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)

Model NO_x Storage Materials at Realistic NO₂ Pressures

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Model NSR catalysts: Fabrication and reactivity of barium oxide layers on Cu(111)

Cited by 45 publications

References 36 publications

Interactive Surface Chemistry of CO2 and NO2 on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

Interactive Surface Chemistry of CO2 and NO2 on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

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

Model NOx Storage Materials at Realistic NO2 Pressures

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Interactive Surface Chemistry of CO₂ and NO₂ on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

Interactive Surface Chemistry of CO₂ and NO₂ on Metal Oxide Surfaces: Competition for Catalytic Adsorption Sites and Reactivity

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)

Model NO_x Storage Materials at Realistic NO₂ Pressures