scholarly journals Rhodium Oxide Surface-Loaded Gas Sensors

Nanomaterials ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 892 ◽  
Author(s):  
Anna Staerz ◽  
Inci Boehme ◽  
David Degler ◽  
Mounib Bahri ◽  
Dmitry Doronkin ◽  
...  
Keyword(s):  
Metal Oxide ◽  
Noble Metal ◽  
Noble Metals ◽  
Metal Cluster ◽  
Empirical Work ◽  
Oxide Surface ◽  
Metallic State ◽  
X Ray ◽  
Rhodium Clusters ◽  
Sensing Characteristics

In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic study of sensors based on rhodium-loaded WO3, SnO2, and In2O3—examined using X-ray diffraction, high-resolution scanning transmission electron microscopy, direct current (DC) resistance measurements, operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and operando X-ray absorption spectroscopy—is presented. Under normal sensing conditions, the rhodium clusters were oxidized. Significant evidence is provided that, in this case, the sensing is dominated by a Fermi-level pinning mechanism, i.e., the reaction with the target gas takes place on the noble-metal cluster, changing its oxidation state. As a result, the heterojunction between the oxidized rhodium clusters and the base metal oxide was altered and a change in the resistance was detected. Through measurements done in low-oxygen background, it was possible to induce a mechanism switch by reducing the clusters to their metallic state. At this point, there was a significant drop in the overall resistance, and the reaction between the target gas and the base material was again visible. For decades, noble metal loading was used to change the characteristics of metal-oxide-based sensors. The study presented here is an attempt to clarify the mechanism responsible for the change. Generalities are shown between the sensing mechanisms of different supporting materials loaded with rhodium, and sample-specific aspects that must be considered are identified.

scholarly journals Study of spatial and temporal aging characteristic of catalyzed diesel particulate filter catalytic performance used for diesel vehicle

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yun-hua Zhang ◽  
Di-ming Lou ◽  
Pi-qiang Tan ◽  
Zhi-yuan Hu
Keyword(s):  
Noble Metal ◽  
Photoelectron Spectroscopy ◽  
Noble Metals ◽  
Catalytic Performance ◽  
Particulate Filter ◽  
Diesel Particulate ◽  
X Ray ◽  
Particulate Filters ◽  
Characteristic Temperatures ◽  
Aging Properties

AbstractCatalyzed diesel particulate filters (CDPFs) have been widespread used as a technically and economically feasible mean for meeting increasingly stringent emissions limits. An important issue affecting the performance of a CDPF is its aging with using time. In this paper, the effects of noble metal loadings, regions and using mileage on the aging performance of a CDPF were investigated by methods of X-ray diffraction (XRD), X-ray photoelectron spectroscopy and catalytic activity evaluation. Results showed that aging of the CDPF shifted the XRD characteristic diffraction peaks towards larger angles and increased the crystallinity, showing a slowing downward trend with the increase of the noble metal loadings. In addition, the increase of the noble metal loading would slow down the decline of Pt and Pt4+ concentration caused by aging. The characteristic temperatures of CO, C3H8 conversion and NO2 production increased after aging, and the more the noble metal loadings, the higher the range of the increase. But noticeably, excessive amounts of noble metals would not present the corresponding anti-aging properties. Specifically, the degree of aging in the inlet region was the deepest, the following is the outlet region, and the middle region was the smallest, which were also reflected in the increase range of crystallinity, characteristic temperatures of CO, C3H8 conversion and NO2 production, as well as the decrease range of Pt and Pt4+ concentrations. The increase of aging mileage reduced the size of the aggregates of the soot and ash in CDPFs, however, improved the degree of tightness between particles. Meanwhile Carbon (C) concentration in the soot and ash increased with the aging mileage.

scholarly journals Nanocrystalline Metal Oxides for Methane Sensors: Role of Noble Metals

2009 ◽  
Vol 2009 ◽  
pp. 1-20 ◽  
Author(s):  
S. Basu ◽  
P. K. Basu
Keyword(s):  
Metal Oxide ◽  
Metal Oxides ◽  
Noble Metal ◽  
Gas Sensors ◽  
Noble Metals ◽  
Industrial Applications ◽  
Metal Catalyst ◽  
Nanocrystalline Metal ◽  
Sensing Properties

Methane is an important gas for domestic and industrial applications and its source is mainly coalmines. Since methane is extremely inflammable in the coalmine atmosphere, it is essential to develop a reliable and relatively inexpensive chemical gas sensor to detect this inflammable gas below its explosion amount in air. The metal oxides have been proved to be potential materials for the development of commercial gas sensors. The functional properties of the metal oxide-based gas sensors can be improved not only by tailoring the crystal size of metal oxides but also by incorporating the noble metal catalyst on nanocrystalline metal oxide matrix. It was observed that the surface modification of nanocrystalline metal oxide thin films by noble metal sensitizers and the use of a noble metal catalytic contact as electrode reduce the operating temperatures appreciably and improve the sensing properties. This review article concentrates on the nanocrystalline metal oxide methane sensors and the role of noble metals on the sensing properties.

The Use of Soft X-Ray Spectroscopy as a Tool for Studying the Surface Region of Metals and Alloys

1972 ◽  
Vol 16 ◽  
pp. 53-62
Author(s):  
J.E. Holliday
Keyword(s):  
Iron Oxide ◽  
Metal Oxide ◽  
Chromium Oxide ◽  
Protective Coating ◽  
Protective Coatings ◽  
Surface Region ◽  
Heat Of Formation ◽  
Metals And Alloys ◽  
Oxide Surface ◽  
X Ray

AbstractThe present investigation shows that soft x-ray spectroscopy is an effective tool for investigating the surface region of metals and alloys from 10 to 1000 Å. Results are presented where soft x-ray spectroscopy was employed to investigate oxidation of metals and alloys, alloy dissolution, and protective coatings. By using the LII/LIII ratio of iron and titanium, the surface oxide thicknesses of these metals could be obtained, For Fe-Cr alloys there is an increase in the amount of chromium relative to chromium oxide with decreasing chormium content. The oxide surface of steel with a 50 Å metal protective coating was reduced when the protective metal oxide had a heat of formation greater than that of iron oxide. In Cu-30Zn alloys, the first 15 min of dissolution showed an increased copper enrichment in the surface of Cu-30Zn.

scholarly journals Evaluation of Metal Oxide Surface Catalysts for the Electrochemical Activation of Amino Acids

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 3144 ◽  
Author(s):  
Christian Tooley ◽  
Charles Gasperoni ◽  
Sabrina Marnoto ◽  
Jeffrey Halpern
Keyword(s):  
Amino Acids ◽  
Metal Oxide ◽  
Electrochemical Detection ◽  
Metal Oxide Nanoparticles ◽  
Schiff Base Complex ◽  
Flow Cell ◽  
Electrochemical Activation ◽  
Oxide Surface ◽  
X Ray ◽  
Metal Oxide Surface

Electrochemical detection of amino acids is important due to their correlation with certain diseases; however, most amino acids require a catalyst to electrochemically activate. One common catalyst for electrochemical detection of amino acids are metal oxides. Metal oxide nanoparticles were electrodeposited onto glassy carbon and platinum working electrodes. Cyclic voltammetry (CV) experiments in a flow cell were performed to evaluate the sensors’ ability to detect arginine, alanine, serine, and valine at micromolar and nanomolar concentrations as high as 4 mM. Solutions were prepared in phosphate buffer saline (PBS) and then 100 mM NaOH. Specifically, NiO surfaces were responsive to amino acids but variable, especially when exposed to arginine. Polarization resistance experiments and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) data indicated that arginine accelerated the corrosion of the NiO catalyst through the formation of a Schiff base complex.

scholarly journals Influence of Semiconductor Morphology on Photocatalytic Activity of Plasmonic Photocatalysts: Titanate Nanowires and Octahedral Anatase Nanoparticles

Nanomaterials ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1447 ◽  
Author(s):  
Wei ◽  
Endo-Kimura ◽  
Wang ◽  
Colbeau-Justin ◽  
Kowalska
Keyword(s):  
Acetic Acid ◽  
Photocatalytic Activity ◽  
Noble Metal ◽  
Photoelectron Spectroscopy ◽  
Noble Metals ◽  
Diffuse Reflectance Spectroscopy ◽  
Localized Surface Plasmon ◽  
Time Resolved ◽  
X Ray ◽  
Titanate Nanowires

Octahedral anatase particles (OAP) with eight exposed and thermodynamically most stable (101) facets were prepared by an ultrasonication-hydrothermal (US-HT) reaction from potassium titanate nanowires (TNW). The precursor (TNW) and the product (OAP) of US-HT reaction were modified with nanoparticles of noble metals (Au, Ag or Pt) by photodeposition. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission electron microscopy (STEM) and time-resolved microwave conductivity (TRMC). The photocatalytic activity was investigated in three reaction systems, i.e., anaerobic dehydrogenation of methanol and oxidative decomposition of acetic acid under UV/vis irradiation, and oxidation of 2-propanol under vis irradiation. It was found that hydrogen liberation correlated with work function of metals, and thus the most active were platinum-modified samples. Photocatalytic activities of bare and modified OAP samples were much higher than those of TNW samples, probably due to anatase presence, higher crystallinity and electron mobility in faceted NPs. Interestingly, noble metals showed different influence on the activity depending on the semiconductor support, i.e., gold-modified TNW and platinum-modified OAP exhibited the highest activity for acetic acid decomposition, whereas silver- and gold-modified samples were the most active under vis irradiation, respectively. It is proposed that the form of noble metal (metallic vs. oxidized) as well as the morphology (well-organized vs. uncontrolled) have a critical effect on the overall photocatalytic performance. TRMC analysis confirmed that fast electron transfer to noble metal is a key factor for UV activity. It is proposed that the efficiency of plasmonic photocatalysis (under vis irradiation) depends on the oxidation form of metal (zero-valent preferable), photoabsorption properties (broad localized surface plasmon resonance (LSPR)), kind of metal (silver) and counteraction of “hot” electrons back transfer to noble metal NPs (by controlled morphology and high crystallinity).

Local Structure of Simplified Waste Glass: Complementarity of XAS and MD Calculations

1997 ◽  
Vol 506 ◽  
Author(s):  
L Galoisy ◽  
J.M. Delaye ◽  
D. Ghaleb ◽  
G. Calas ◽  
M. Le Grand ◽  
...  
Keyword(s):  
Noble Metal ◽  
Local Structure ◽  
Noble Metals ◽  
Coordination Shell ◽  
Waste Glass ◽  
Oxide Glass ◽  
Glassy Matrix ◽  
Borosilicate Glasses ◽  
X Ray ◽  
Te Precipitates

ABSTRACTX-ray Absorption Spectroscopy (XAS) together with x-ray diffraction methods were used in inactive analogues of the French nuclear waste glass to analyze Pd-Te precipitates and the peculiarity of the sites occupied by some structural probe elements such as Mo, Zn, Zr and Si in the glassy part of the material. The influence of the precipitates on the structure of the glassy matrix around these structural probes was investigated by comparing noble metal bearing compositions together with noble metal free glasses.In noble metal bearing glasses, Pd is associated to Te as (Pd90 Te10) precipitates. Pd K-edge EXAFS shows the presence of Te in the Pd coordination shell and is in accordance with a non-metallic character of the Pd-Te bond. Mo K-edge EXAFS shows that Mo occurs as molybdate groups non connected to the glassy matrix, which may be related to the occasional separation of Mo-rich phases in some compositions. Zr is located in an octahedron with d(Zr-O)=2.08Å 0.01Å whereas Zn is 4-fold coordinated with d(Zn-0)=-1.95 ű 0.01Å. Beyond this well defined first coordination shell, XAS detects some degree of medium range order which gives insight on the bonding of the site to the polymeric borosilicate network. The interatomic Zn-Si and Zr-Si EXAFS-determined distances agree with a ZnO4 and Si04 tetrahedra sharing corners geometry and Zr-Si octahedra sharing corner with Si04 tetrahedra. A third shell of neighbors around Zr was evidenced in the noble metal bearing glasses and in a four oxide glass, indicating that Zr is an element useful for detecting subtle changes in the local structure of complex borosilicate glasses. Si K XANES shows modifications in the connection between Si04 tetrahedra when noble metals are present. To obtain accurate and precise structural interpretations, a direct comparison between EXAFS data and Molecular Dynamic (M.D.) calculations on simplified nuclear glass comprising six oxides has been performed. MD calculations show that the distribution of the Zr-O distances is harmonic in the k-range accessible with EXAFS in glasses.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

scholarly journals Biodiesel Production on Monometallic Pt, Pd, Ru, and Ag Catalysts Supported on Natural Zeolite

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 48
Author(s):  
Pawel Mierczynski ◽  
Magdalena Mosińska ◽  
Lukasz Szkudlarek ◽  
Karolina Chalupka ◽  
Misa Tatsuzawa ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Natural Zeolite ◽  
Noble Metals ◽  
Methyl Esters ◽  
Physicochemical Characteristics ◽  
Biodiesel Production ◽  
X Ray Diffraction ◽  
X Ray ◽  
Yield Values ◽  
Temperature Programmed

Biodiesel production from rapeseed oil and methanol via transesterification reaction facilitated by various monometallic catalyst supported on natural zeolite (NZ) was investigated. The physicochemical characteristics of the synthesized catalysts were studied by X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), temperature-programmed-reduction in hydrogen (H2-TPR), temperature-programmed-desorption of ammonia (NH3-TPD), Scanning Electron Microscope equipped with EDX detector (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) methods. The highest activity and methyl ester yields were obtained for the Pt/NZ catalyst. This catalyst showed the highest triglycerides conversion of 98.9% and fatty acids methyl esters yields of 94.6%. The activity results also confirmed the high activity of the carrier material (NZ) itself in the investigated reaction. Support material exhibited 90.5% of TG conversion and the Fatty Acid Methyl Esters yield (FAME) of 67.2%. Introduction of noble metals improves the TG conversion and FAME yield values. Increasing of the metal loading from 0.5 to 2 wt.% improves the reactivity properties of the investigated catalysts.

Adsorption of the Gas Molecules (NH3, C2H6O, C3H6O, CO, H2S) on noble metal (Ag, Au, Pt, Pd, Ru)–Doped MoSe2 Monolayer: A First-Principles Study

2021 ◽  
Author(s):  
Lanjuan Zhou ◽  
Sujing Yu ◽  
Yan Yang ◽  
Qi Li ◽  
Tingting Li ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Noble Metal ◽  
First Principles ◽  
Density Functional ◽  
Noble Metals ◽  
Gas Sensing ◽  
Functional Theory ◽  
First Principles Study ◽  
Gas Molecules ◽  
Sensing Performance

In this paper, the effects of five noble metals (Au, Pt, Pd, Ag, Ru) doped MoSe2 on improving gas sensing performance were predicted through density functional theory (DFT) based on...

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