scholarly journals Raman Spectroscopy for Characterization of Hydrotalcite-like Materials Used in Catalytic Reactions

2021 ◽  
Author(s):  
Luciano Honorato Chagas ◽  
Sandra Shirley Ximeno Chiaro ◽  
Alexandre Amaral Leitão ◽  
Renata Diniz
Keyword(s):  
Raman Spectroscopy ◽  
Density Functional ◽  
Mixed Oxides ◽  
Structural Characteristics ◽  
Catalytic Reactions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Programmed ◽  
Materials Used

This chapter covers a brief review of the definition, structural characteristics and main applications of hydrotalcite, an interesting multifunctional material which finds applicability in different areas. Particularly, some catalytic reactions using hydrotalcite or mixed oxides derived from these materials are addressed (Ethanol Steam Reforming, Photochemical conversions, Hydrodesulfurization). The use of Raman Spectroscopy associated with other techniques, such as powder X-ray diffraction (XRD), Extended X-ray Absorption Fine-Structure (EXAFS), Temperature Programmed Reduction of hydrogen (H2-TPR), Fourier-Transform Infrared (FTIR) and Density Functional Theory (DFT) simulations, to characterize this type of material is addressed through examples described in the current literature. In this sense, multidisciplinary efforts must be made in order to increase the understanding of the properties of these materials and the catalytic behavior in the most varied reactions.

scholarly journals Metal-Rich Metallaboranes: Synthesis, Structures and Bonding of Bi- and Trimetallic Open-Faced Cobaltaboranes

Inorganics ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 28
Author(s):  
Kriti Pathak ◽  
Chandan Nandi ◽  
Jean-François Halet ◽  
Sundargopal Ghosh
Keyword(s):  
Electronic Structures ◽  
Density Functional ◽  
Room Temperature ◽  
Electron Pair ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Cluster 2 ◽  
Cobalt Center

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions of monoborane as well as modified borohydride reagents with cobalt sources. For example, the reaction of [Cp*CoCl]2 with [LiBH4·THF] and subsequent photolysis with excess [BH3·THF] (THF = tetrahydrofuran) at room temperature afforded the 11-vertex tricobaltaborane nido-[(Cp*Co)3B8H10] (1, Cp* = η5-C5Me5). The reaction of Li[BH2S3] with the dicobaltaoctaborane(12) [(Cp*Co)2B6H10] yielded the 10-vertex nido-2,4-[(Cp*Co)2B8H12] cluster (2), extending the library of dicobaltadecaborane(14) analogues. Although cluster 1 adopts a classical 11-vertex-nido-geometry with one cobalt center and four boron atoms forming the open pentagonal face, it disobeys the Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound 2 adopts a perfectly symmetrical 10-vertex-nido framework with a plane of symmetry bisecting the basal boron plane resulting in two {CoB3} units bridged at the base by two boron atoms and possesses the expected electron count. Both compounds were characterized in solution by multinuclear NMR and IR spectroscopies and by mass spectrometry. Single-crystal X-ray diffraction analyses confirmed the structures of the compounds. Additionally, density functional theory (DFT) calculations were performed in order to study and interpret the nature of bonding and electronic structures of these complexes.

Deposition of TRISO Particles With Superhard SiC Coatings and the Characterization of Anisotropy by Raman Spectroscopy

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
E. López-Honorato ◽  
P. J. Meadows ◽  
J. Tan ◽  
Y. Xiang ◽  
P. Xiao
Keyword(s):  
Solid Solution ◽  
Raman Spectroscopy ◽  
Pyrolytic Carbon ◽  
X Ray Diffraction ◽  
X Ray ◽  
Flat Substrate ◽  
High Concentrations ◽  
Triso Particles ◽  
Sic Coatings

In this work we have deposited silicon carbide (SiC) at 1300°C with the addition of small amounts of propylene. The use of propylene and high concentrations of methyltrichlorosilane (9 vol %) allowed the deposition of superhard SiC coatings (42 GPa). The superhard SiC could result from the presence of a SiC–C solid solution, undetectable by X-ray diffraction but visible by Raman spectroscopy. Another sample obtained by the use of 50 vol % Argon, also showed the formation of SiC with good properties. The use of a flat substrate together with the particles showed the importance of carrying out the analysis on actual particles rather than in flat substrates. We show that it is possible to characterize the anisotropy of pyrolytic carbon by Raman spectroscopy.

scholarly journals Synthesis and Characterization of K-Ta Mixed Oxides for Hydrogen Generation in Photocatalysis

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Beata Zielińska ◽  
Ewa Mijowska ◽  
Ryszard J. Kalenczuk
Keyword(s):  
Diffuse Reflectance ◽  
Hydrogen Generation ◽  
Mixed Oxides ◽  
X Ray Diffraction ◽  
X Ray ◽  
Raman Spectroscopic ◽  
Photocatalytic Hydrogen Generation ◽  
Irregular Structure ◽  
Transmission Electron

K-Ta mixed oxides photocatalysts have been prepared by impregnation followed by calcination. The influence of the reaction temperature (450°C–900°C) on the phase formation, crystal morphology, and photocatalytic activity in hydrogen generation of the produced materials was investigated. The detailed analysis has revealed that all products exhibit high crystallinity and irregular structure. Moreover, two different crystal structures of potassium tantalates such as KTaO3and K2Ta4O11were obtained. It was also found that the sample composed of KTaO3and traces of unreacted Ta2O5(annealed at 600°C) exhibits the highest activity in the reaction of photocatalytic hydrogen generation. The crystallographic phases, optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-ray spectrometer (EDX) as its mode.

Characterization of Cold Sprayed Copper Coatings on Al Alloy Substrate

2015 ◽  
Vol 3 (2) ◽  
pp. 41-53
Author(s):  
Tarun Goyal ◽  
T. S. Sidhu ◽  
R. S. Walia
Keyword(s):  
Spray Deposition ◽  
Structural Characteristics ◽  
Al Alloy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Copper Coatings ◽  
Powder Particles ◽  
Micro Analysis ◽  
Hardness Values

This study reveals the successful low pressure cold spray deposition of near-uniform, defect free and dense copper coatings approximately 700-1900 µm thick, on Al alloy for electro-technical applications. The micro structural characteristics of the deposits have been studied using the combined techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) and electron-probe micro analysis (EPMA). The coatings exhibited characteristic splat-like, layered morphologies due to the deposition of solid powder particles which appeared to have been plastically deformed on impact to the substrate. The developed coatings have a dense (in the range of 3090-5015 kg/m3)and nearly uniform microstructure, with almost uniform hardness values in the range of 120 -140 Hv, and electrical conductivity in the range of 23-30 MS/m. EDAX, XRD and EPMA results revealed that the main constituent in the coating is Cu.

scholarly journals A High-Pressure Investigation of the Synthetic Analogue of Chalcomenite, CuSeO3∙2H2O

Crystals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 643 ◽  
Author(s):  
Javier Gonzalez-Platas ◽  
Placida Rodriguez-Hernandez ◽  
Alfonso Muñoz ◽  
U. R. Rodríguez-Mendoza ◽  
Gwilherm Nénert ◽  
...  
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
Raman Spectroscopy ◽  
Pressure Dependence ◽  
Density Functional ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Raman Modes

Synthetic chalcomenite-type cupric selenite CuSeO3∙2H2O has been studied at room temperature under compression up to pressures of 8 GPa by means of single-crystal X-ray diffraction, Raman spectroscopy, and density-functional theory. According to X-ray diffraction, the orthorhombic phase undergoes an isostructural phase transition at 4.0(5) GPa with the thermodynamic character being first-order. This conclusion is supported by Raman spectroscopy studies that have detected the phase transition at 4.5(2) GPa and by the first-principles computing simulations. The structure solution at different pressures has provided information on the change with pressure of unit–cell parameters as well as on the bond and polyhedral compressibility. A Birch–Murnaghan equation of state has been fitted to the unit–cell volume data. We found that chalcomenite is highly compressible with a bulk modulus of 42–49 GPa. The possible mechanism driving changes in the crystal structure is discussed, being the behavior of CuSeO3∙2H2O mainly dominated by the large compressibility of the coordination polyhedron of Cu. On top of that, an assignation of Raman modes is proposed based upon density-functional theory and the pressure dependence of Raman modes discussed. Finally, the pressure dependence of phonon frequencies experimentally determined is also reported.

scholarly journals Ce- and Y-Modified Double-Layered Hydroxides as Catalysts for Dry Reforming of Methane: On the Effect of Yttrium Promotion

Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 56 ◽  
Author(s):  
Katarzyna Świrk ◽  
Magnus Rønning ◽  
Monika Motak ◽  
Patricia Beaunier ◽  
Patrick Da Costa ◽  
...  
Keyword(s):  
Textural Properties ◽  
Dry Reforming ◽  
Dry Reforming Of Methane ◽  
Side Reactions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Temperature Programmed ◽  
Nickel Species

Ce- and Y-promoted double-layered hydroxides were synthesized and tested in dry reforming of methane (CH4/CO2 = 1/1). The characterization of the catalysts was performed using X-ray fluorescence (XRF), X-ray diffraction (XRD), N2 sorption, temperature-programmed reduction in H2 (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), H2 chemisorption, thermogravimetric analysis coupled by mass spectrometry (TGA/MS), Raman, and high-resolution transmission electron microscopy (HRTEM). The promotion with cerium influences textural properties, improves the Ni dispersion, decreases the number of total basic sites, and increases the reduction temperature of nickel species. After promotion with yttrium, the increase in basicity is not directly correlated with the increasing Y loading on the contrary of Ni dispersion. Dry reforming of methane (DRM) was performed as a function of temperature and in isothermal conditions at 700 °C for 5 h. For catalytic tests, a slight increase of the activity is observed for both Y and Ce doped catalysts. This improvement can of course be explained by Ni dispersion, which was found higher for both Y and Ce promoted catalysts. During DRM, the H2/CO ratio was found below unity, which can be explained by side reactions occurrence. These side reactions are linked with the increase of CO2 conversion and led to carbon deposition. By HRTEM, only multi-walled and helical-shaped carbon nanotubes were identified on Y and Ce promoted catalysts. Finally, from Raman spectroscopy, it was found that on Y and Ce promoted catalysts, the formed C is less graphitic as compared to only Ce-based catalyst.

scholarly journals Bulk Versus Surface Modification of Alumina with Mn and Ce Based Oxides for CH4 Catalytic Combustion

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1771 ◽  
Author(s):  
Stefan Neatu ◽  
Mihaela M. Trandafir ◽  
Adelina Stănoiu ◽  
Ovidiu G. Florea ◽  
Cristian E. Simion ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Catalytic Combustion ◽  
Mixed Oxides ◽  
Sol Gel ◽  
Nitrogen Adsorption ◽  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Programmed ◽  
Catalytic Combustion Of Methane ◽  
Adsorption Desorption

This study presents the synthesis and characterization of lanthanum-modified alumina supported cerium–manganese mixed oxides, which were prepared by three different methods (coprecipitation, impregnation and citrate-based sol-gel method) followed by calcination at 500 °C. The physicochemical properties of the synthesized materials were investigated by various characterization techniques, namely: nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and H2–temperature programmed reduction (TPR). This experimental study demonstrated that the role of the catalytic surface is much more important than the bulk one. Indeed, the incipient impregnation of CeO2–MnOx catalyst, supported on an optimized amount of 4 wt.% La2O3–Al2O3, provided the best results of the catalytic combustion of methane on our catalytic micro-convertors. This is mainly due to: (i) the highest pore size dimensions according to the Brunauer-Emmett-Teller (BET) investigations, (ii) the highest amount of Mn4+ or/and Ce4+ on the surface as revealed by XPS, (iii) the presence of a mixed phase (Ce2MnO6) as shown by X-ray diffraction; and (iv) a higher reducibility of Mn4+ or/and Ce4+ species as displayed by H2–TPR and therefore more reactive oxygen species.

Characterization of Pd–Au/SiO2 Catalysts by X-ray Diffraction, Temperature-Programmed Hydride Decomposition, and Catalytic Probes

2000 ◽  
Vol 195 (2) ◽  
pp. 304-315 ◽  
Author(s):  
M. Bonarowska ◽  
J. Pielaszek ◽  
W. Juszczyk ◽  
Z. Karpiński
Keyword(s):  
X Ray Diffraction ◽  
X Ray ◽  
Temperature Programmed

scholarly journals Synchrotron X-ray diffraction characterization of the inheritance of GaN homoepitaxial thin films grown on selective growth substrates

CrystEngComm ◽  
2018 ◽  
Vol 20 (20) ◽  
pp. 2861-2867 ◽  
Author(s):  
Yanfang Lou ◽  
Chulho Song ◽  
Yanna Chen ◽  
Loku Singgappulige Rosantha Kumara ◽  
Natalia Palina ◽  
...  
Keyword(s):  
Thin Films ◽  
Structural Characteristics ◽  
Selective Growth ◽  
X Ray Diffraction ◽  
X Ray ◽  
Growth Substrates

The structural characteristics of a selective growth GaN substrate were inherited from an Al2O3 substrate and then transferred to homoepitaxial thin films.

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