Enhanced CO Oxidation Catalysis of Pt0.1Cu0.9/Fe2O3 Synthesized by Radiolytic Process

2011 ◽  
Vol 1311 ◽  
Author(s):  
Takao A. Yamamoto ◽  
Ryota Kitagawa ◽  
Satoshi Seino ◽  
Takashi Nakagawa
Keyword(s):  
Co Oxidation ◽  
Gas Flow ◽  
Hydrogen Gas ◽  
Oxidation Catalysis ◽  
Polymer Electrolyte Fuel Cell ◽  
Commercial Catalyst ◽  
Edge Structure ◽  
X Ray ◽  
Radiolytic Process ◽  
Increasing Temperature

ABSTRACTCatalysts in which Pt and Cu are immobilized on support particles of γ-Fe2O3 were synthesized by the radiolytic process and were evaluated for CO oxidation in a gas flow mixture (1% CO, 0.5% O2, 67.2% H2 and N2 balance) by measuring the CO concentration in the outlet gas. The Pt/Cu atomic ratios of the as-synthesized catalysts were determined to be 100:0, 90:10, 78:22, 50:50, 21:79, and 11:89, and the total metal loadings determined by chemical analyses were 10 wt%. Material characterization was performed using X-ray diffraction, X-ray absorption near edge structure, and transmission electron microscopy, and it was indicated that the composite catalysts consist of Pt-Cu bimetallic grains immobilized on the support at higher Pt-loading, while CuO with poor crystallinity is also observed at lower Pt-loading. The catalytic activity decreased as the Pt-loading was decreased to 50 at%, and also with increasing temperature. However, as the Pt-loading was further decreased, the activity contrariwise increased, and increased with increasing temperature up to 100 °C. The sample containing only 11 at% Pt exhibited the highest activity at 100 °C, which is higher than that of the commercial catalyst measured for comparison, and given at a lower temperature than that for the commercial catalyst. This enhanced activity, despite the low Pt-loading, could be attributed to oxygen supply via CuO from the O2-poor atmosphere to PtCu bimetallic grains trapping CO molecules. This new material is promising for use as a catalyst to purify hydrogen gas fed to a polymer electrolyte fuel cell.

Bimetallic Nanoparticles of PtCu and PtNi; Synthesis and CO Oxidation Catalysis

2009 ◽  
Vol 1217 ◽  
Author(s):  
Takao A. Yamamoto ◽  
Takashi Nakagawa ◽  
Satoshi Seino ◽  
Hiroaki Nitani
Keyword(s):  
Electron Beam ◽  
Co Oxidation ◽  
Bimetallic Nanoparticles ◽  
Hydrogen Gas ◽  
Oxidation Catalysis ◽  
Water Radiolysis ◽  
Metallic State ◽  
Iron Oxide Particles ◽  
Preferential Oxidation Of Co ◽  
Aqueous Ions

AbstractBimetallic nanoparticles of PtCu and PtNi supported on iron oxide particles were synthesized by a new method employing a 4.8-MeV electron beam as a trigger for reduction of their aqueous ions, and their CO oxidation catalysis was evaluated to find activities enhanced by the alloying. Sample materials of PtCu (PtNi) bimetallic grains supported on γ-Fe2O3 particles were synthesized by irradiating with the electron beam a glass vial containing precursors in an aqueous solution. The vial contains aqueous ions of platinum and copper (nickel) and γ-Fe2O3 particles of average size of 30 nm. The irradiation induces water radiolysis generating reducing species, such as hydrated electrons, and metallic nanograins are formed and stabilized on the support material. The irradiation was finished in several seconds without using any organic solvent and any surfactant. The average grain sizes observed with a TEM were around 3 nm in diameter. XRD patterns of PtCu samples exhibited the FCC structure with peak shifts obeying the Vegard’s law at low Cu concentrations. X-ray absorption spectra measured at edges of the constituent elements indicated that Pt is in the metallic state and coordinates certainly with Cu or Ni. Catalytic activity of CO oxidation of the material was evaluated by measuring residual CO contents in air in contact with the sample material by using a gas-chromatograph. The activities of the PtCu and PtNi samples were higher than that of monolithic Pt on γ-Fe2O3. The correlation between the atomic structure in these nanograins and their activities was investigated, which indicated that the random alloy enhances the activity. These bimetallic nanoparticles are expected as catalysts for preferential oxidation of CO in hydrogen gas fed to fuel cells.

scholarly journals Structural and In Situ X-ray Diffraction Study of Hydrogenation of CaxMg1−xNi2 (0 ≤ x ≤ 1)

Crystals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 47
Author(s):  
Zia Ur Rehman ◽  
Mohsan Nawaz ◽  
Hameed Ullah ◽  
Pervaiz Ahmad ◽  
Mayeen Uddin Khandaker ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Powder Diffraction ◽  
Gas Flow ◽  
Hydrogen Gas ◽  
Laves Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Phase Type ◽  
Diffraction Patterns

In the quasi-binary system CaNi2-MgNi2 solid-solutions CaxMg1−xNi2 (0 ≤ x ≤ 1) were prepared from the elements. They crystallize in the hexagonal Laves phase type (MgNi2, C36) for x ≤ 0.33 (P63/mmc, a = 482.51(7) pm, c = 1582.1(3) pm for x = 0, a = 482.59 (3), c = 1583.1(1) for x = 0.33) and in the cubic Laves phase type (MgCu2, C15) for 0.33 < x (Fd−3m, a = 697.12(3) pm for x = 0.5, a = 705.11(2) pm for x = 0.67, a = 724.80(2) pm for x = 1). After hydrogenation in an autoclave the X-ray diffraction patterns changed completely. Reflections assigned to CaNiH3, and Ni and Rietveld refinement confirmed this. The hydrogenation properties of CaxMg1−xNi2 (0 ≤ x ≤ 1) compounds were also studied in situ by X-ray powder diffraction. In situ X-ray powder diffraction of CaxMg1−xNi2 (0 ≤ x ≤ 1) compounds under 0.3 MPa hydrogen gas flow (15 sccm), data collected on a Rigaku SmartLab diffractometer in an Anton Paar XRK 900 Reactor Chamber using Cu-Kα1 radiation. Scanning electron microscopy and EDX spectroscopy confirmed the entitled materials and elemental composition, respectively. From the Transmission electron microscopy and Selected area electron diffraction concluded that the CaxMg1−xNi2 (0 ≤ x ≤ 1) compounds were crystalline.

scholarly journals Defect Passivation and Carrier Reduction Mechanisms in Hydrogen-Doped In-Ga-Zn-O (IGZO:H) Films upon Low-Temperature Annealing for Flexible Device Applications

Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 334
Author(s):  
Rostislav Velichko ◽  
Yusaku Magari ◽  
Mamoru Furuta
Keyword(s):  
Low Temperature ◽  
Photoelectron Spectroscopy ◽  
Oxygen Diffusion ◽  
Gas Flow ◽  
Hydrogen Gas ◽  
Oxide Semiconductor ◽  
Activation Temperature ◽  
X Ray ◽  
Gas Flow Ratio ◽  
Temperature Activation

Low-temperature activation of oxide semiconductor materials such as In-Ga-Zn-O (IGZO) is a key approach for their utilization in flexible devices. We previously reported that the activation temperature can be reduced to 150 °C by hydrogen-doped IGZO (IGZO:H), demonstrating a strong potential of this approach. In this paper, we investigated the mechanism for reducing the activation temperature of the IGZO:H films. In situ Hall measurements revealed that oxygen diffusion from annealing ambient into the conventional Ar/O2-sputtered IGZO film was observed at >240 °C. Moreover, the temperature at which the oxygen diffusion starts into the film significantly decreased to 100 °C for the IGZO:H film deposited at hydrogen gas flow ratio (R[H2]) of 8%. Hard X-ray photoelectron spectroscopy indicated that the near Fermi level (EF) defects in the IGZO:H film after the 150 °C annealing decreased in comparison to that in the conventional IGZO film after 300 °C annealing. The oxygen diffusion into the film during annealing plays an important role for reducing oxygen vacancies and subgap states especially for near EF. X-ray reflectometry analysis revealed that the film density of the IGZO:H decreased with an increase in R[H2] which would be the possible cause for facilitating the O diffusion at low temperature.

Cathodoluminescence, X-ray excited optical luminescence, and X-ray absorption near-edge structure studies of ZnO nanostructures

2012 ◽  
Vol 90 (3) ◽  
pp. 298-305 ◽  
Author(s):  
Olga Lobacheva ◽  
Patricia L. Corcoran ◽  
Michael W. Murphy ◽  
Jun Young Peter Ko ◽  
Tsun-Kong Sham
Keyword(s):  
Gas Flow ◽  
Branching Ratio ◽  
Optical Emission ◽  
Zno Nanostructures ◽  
Edge Structure ◽  
X Ray ◽  
Synthesis Parameters ◽  
Optical Luminescence ◽  
Carrier Gas Flow ◽  
X Ray Absorption

ZnO nanostructures of various morphologies and crystallinities were fabricated by thermal evaporation from Zn powder in a tube furnace in the presence of oxygen. It was found that the morphology of ZnO nanostructures was affected by synthesis parameters, such as growth temperature, carrier gas flow, and the presence of catalyst on the surface of the substrate. Representative ZnO nanostructures were studied by X-ray excited optical luminescence (XEOL) and cathodoluminescence (CL) methods. The luminescence from these samples exhibits a morphology dependence of the branching ratio of the near band gap (NBG) emission in the UV and defect emission in the green (GE). The appearance of the optical emission also depends on the excitation method. X-ray absorption near-edge structures (XANES) at the O K-edge and Zn L-edge are also presented and their implications discussed.

Morphology-dependent luminescence from ZnO nanostructures — An X-ray excited optical luminescence study at the Zn K-edge

2009 ◽  
Vol 87 (9) ◽  
pp. 1255-1260 ◽  
Author(s):  
Olga Lobacheva ◽  
Michael W. Murphy ◽  
Jun Young Peter Ko ◽  
Tsun-Kong Sham
Keyword(s):  
Gas Flow ◽  
Thermal Evaporation ◽  
Growth Conditions ◽  
Zno Nanostructures ◽  
Edge Structure ◽  
X Ray ◽  
Si Substrates ◽  
Optical Luminescence ◽  
Carrier Gas Flow ◽  
X Ray Absorption

ZnO nanostructures have been synthesized by thermal evaporation on Si substrates. It is found that the morphologies of the nanostructures are governed by growth conditions such as temperature, carrier-gas flow rate, and the nature of the substrate (with and without a catalyst). We report X-ray excited optical luminescence from ZnO nanostructures of distinctly different morphologies in the energy and time domain using excitation photon energies across the Zn K-edge. X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) study has clearly shown the morphology dependence of the ZnO optical properties. A correlation of luminescence with morphology, size, and crystallinity emerges.

scholarly journals Ultra-Small Pd Nanoparticles on Ceria as an Advanced Catalyst for CO Oxidation

Catalysts ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 385 ◽  
Author(s):  
Andrei Tereshchenko ◽  
Vladimir Polyakov ◽  
Alexander Guda ◽  
Tatiana Lastovina ◽  
Yulia Pimonova ◽  
...  
Keyword(s):  
Co Oxidation ◽  
Pd Nanoparticles ◽  
High Dispersion ◽  
High Catalytic Activity ◽  
Drift Spectroscopy ◽  
Edge Structure ◽  
X Ray ◽  
Co Oxidation Reaction ◽  
Ceria Support ◽  
Co Probe

In this study, we demonstrate the preparation and characterization of small palladium nanoparticles (Pd NPs) on modified ceria support (Pd/CeO2) using wet impregnation and further reduction in an H2/Ar flow. The obtained particles had a good dispersion, but their small size made it difficult to analyze them by conventional techniques such as transmission electron microscopy (TEM) and X-ray powder diffraction (XRPD). The material demonstrated a high catalytic activity in the CO oxidation reaction: the 100% of CO conversion was achieved at ~50 °C, whereas for most of the cited literature, such a high conversion usually was observed near 100 °C or higher for Pd NPs. Diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy in combination with CO probe molecules was used to investigate the size and morphology of NPs and the ceria support. On the basis of the area ratio under the peaks attributed to bridged (B) and linear (L) carbonyls, high-dispersion Pd NPs was corroborated. Obtained results were in good agreement with data of X-ray absorption near edge structure analysis (XANES) and CO chemisorption measurements.

Chemical and orientational imaging of polymeric samples

1994 ◽  
Vol 52 ◽  
pp. 68-69
Author(s):  
H. Ade ◽  
B. Hsiao ◽  
G. Mitchell ◽  
E. Rightor ◽  
A. P. Smith ◽  
...  
Keyword(s):  
Ethylene Terephthalate ◽  
National Laboratory ◽  
Brookhaven National Laboratory ◽  
Carbonyl Groups ◽  
Aromatic Rings ◽  
Edge Structure ◽  
X Ray ◽  
Scanning Transmission ◽  
Polymeric Samples ◽  
X Ray Absorption

We have used the Scanning Transmission X-ray Microscope at beamline X1A (X1-STXM) at Brookhaven National Laboratory (BNL) to acquire high resolution, chemical and orientation sensitive images of polymeric samples as well as point spectra from 0.1 μm areas. This sensitivity is achieved by exploiting the X-ray Absorption Near Edge Structure (XANES) of the carbon K edge. One of the most illustrative example of the chemical sensitivity achievable is provided by images of a polycarbonate/pol(ethylene terephthalate) (70/30 PC/PET) blend. Contrast reversal at high overall contrast is observed between images acquired at 285.36 and 285.69 eV (Fig. 1). Contrast in these images is achieved by exploring subtle differences between resonances associated with the π bonds (sp hybridization) of the aromatic groups of each polymer. PET has a split peak associated with these aromatic groups, due to the proximity of its carbonyl groups to its aromatic rings, whereas PC has only a single peak.

Electron Microscopy/Diffraction Study of the Ternary Mn-Er-S System

1990 ◽  
Vol 48 (1) ◽  
pp. 76-77
Author(s):  
A. R. Landa Canovas ◽  
L.C. Otero Diaz ◽  
T. White ◽  
B.G. Hyde
Keyword(s):  
Electron Microscopy ◽  
Gas Flow ◽  
Graphite Crucible ◽  
Nominal Composition ◽  
X Ray Diffraction ◽  
Alumina Crucible ◽  
X Ray ◽  
Intermediate Phases ◽  
Twin Band ◽  
Ar Gas

X-Ray diffraction revealed two intermediate phases in the system MnS+Er2S3,:MnEr2S4= MnS.Er2S3, and MnEr4S7= MnS.2Er2S3. Their structures may be described as NaCl type, chemically twinned at the unit cell level, and isostructural with CaTi2O4, and Y5S7 respectively; i.e. {l13} NaCl twin band widths are (4,4) and (4,3).The present study was to search for structurally-related (twinned B.) structures and or possible disorder, using the more sensitive and appropiate technigue of electron microscopy/diffraction.A sample with nominal composition MnEr2S4 was made by heating Mn3O4 and Er2O3 in a graphite crucible and a 5% H2S in Ar gas flow at 1500°C for 4 hours. A small amount of this material was thenannealed, in an alumina crucible, contained in sealed evacuated silica tube, for 24 days at 1100°C. Both samples were studied by X-ray powder diffraction, and in JEOL 2000 FX and 4000 EX microscopes.

Tuning the Activities of Cu2O Nanostructures via the Oxide-Metal Interaction

2019 ◽  
Author(s):  
Wugen Huang ◽  
qingfei liu ◽  
Zhiwen Zhou ◽  
Yangsheng Li ◽  
Yong Wang ◽  
...  
Keyword(s):  
Co Oxidation ◽  
Oxidation Catalysis ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Oxidation Reactions ◽  
Tunneling Microscopy ◽  
Temperature Oxidation ◽  
Metal Interaction ◽  
Tremendous Importance ◽  
Oxygen Atoms

Despite tremendous importance in catalysis, the design and improvement of the oxide- metal interface has been hampered by the limited understanding on the nature of interfacial sites, as well as the oxide-metal interaction (OMI). Through the construction of well-defined Cu<sub>2</sub>O-Pt, Cu<sub>2</sub>O-Ag, Cu<sub>2</sub>O-Au interfaces, we found that Cu<sub>2</sub>O Nanostructures (NSs) on Pt exhibit much lower thermal stability than on Ag and Au, although they show the same surface and edge structures, as identified by element-specific scanning tunneling microscopy (ES-STM) images. The activities of the Cu<sub>2</sub>O-Pt and Cu<sub>2</sub>O-Au interfaces for CO oxidation were further compared at the atomic scale and showed in general that the interface with Cu<sub>2</sub>O NSs could annihilate the CO-poisoning problem suffered by Pt group metals and enhance the interaction with O<sub>2</sub>, which is a limiting step for CO oxidation catalysis on group IB metals. While both interfaces could react with CO at room temperature, the OMI was found to determine the reactivity of supported Cu<sub>2</sub>O NSs by 1) tuning the activity of interfacial oxygen atoms and 2) stabilizing oxygen vacancies or vice versa, the dissociated oxygen atoms at the interface. Our study provides new insight for OMI and for the development of Cu-based catalysts for low temperature oxidation reactions.

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