Structure, Chemical Composition, and Catalytic Behaviour of Stoichiometric and Non-Stoichiometric LaMnO3 Toward Deep Oxidation of Ethanol

2015 ◽  
Vol 68 (12) ◽  
pp. 1900
Author(s):  
Hammami Ramzi ◽  
Habib Batis
Keyword(s):  
Oxidation State ◽  
Co2 Adsorption ◽  
Deep Oxidation ◽  
Oxygen Storage ◽  
Crystalline Lattice ◽  
Basic Site ◽  
Material Surface ◽  
X Ray ◽  
Surface Basicity ◽  
Positive Holes

A series of structurally modified LarMnO3±δ (r = 0.80, 1.00, 1.25) perovskites have been investigated for ethanol deep oxidation in the temperature range 100–300°C. The catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), redox titration and CO2 adsorption. All samples are single perovskite phases without segregated phases. For La- and Mn-under-stoichiometric samples, the defects generated to maintain structure electroneutrality are positive holes and anion vacancies whereas for stoichiometric solids, the defects are positive holes and cation vacancies. The surface oxidation state and composition are critically controlled by the phase composition of the bulk. XPS results showed that the decrease in bulk La/Mn ratio induced a decrease in surface La enrichment. A concomitant decrease of basic site concentration was shown by CO2 adsorption. With lower surface La content, excess Mn sites and increasing concentrations of surface Mn4+ were observed. Catalytic properties in the oxidation reaction of ethanol are attributed to the variability of the manganese oxidation state, basic character of the material surface, which is related to the La/Mn atomic ratio, and to the oxygen storage capacity in the crystalline lattice of the catalysts. It was shown that La0.8MnO3–δ presents the best catalytic activity, due to low surface basicity (lowest La/Mn ratio) and high redox properties (highest Mn4+/Mn3+ ratio).

scholarly journals Synthesis and Characterization of Co-Doped Fly Ash Catalyst for Chalcone Synthesis

2019 ◽  
Vol 31 (10) ◽  
pp. 2165-2172 ◽  
Author(s):  
U.G. Ghoshir ◽  
S.R. Kande ◽  
G.G. Muley ◽  
A.B. Gambhire
Keyword(s):  
Electron Microscopy ◽  
Fly Ash ◽  
Hybrid Materials ◽  
Hybrid Material ◽  
Alkaline Earth ◽  
Alkaline Earth Metals ◽  
Basic Site ◽  
X Ray ◽  
Surface Basicity ◽  
Co Doped

A series of solid base fly ash hybrid materials were synthesized by doping alkali, alkaline earth metals with nitrogen, separately using co-precipitation process, combined with surfactant incorporating method. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. Results revealed that the co-doped hybrid materials are highly stable with particle size in the range of 40-60 nm. The surface basicity of fly ash was upraised by increased hydroxyl content by doping with alkali, alkaline earth metals with nitrogen. The basicity of hybrid material was measured by liquid phase, solvent free, single step condensation of 4-chlorobenzaldehyde and acetophenone giving higher conversion rate and selectivity of desired product chalcone. This conversion showed that the fly ash based hybrid material has sufficient basic site, responsible for the catalytic activity

scholarly journals Probing physical oxidation state via resonant X‐ray emission spectroscopy: Applications to iron model complexes and nitrogenase

2021 ◽  
Author(s):  
Serena DeBeer ◽  
Rebeca G. Castillo ◽  
Anselm W. Hahn ◽  
Benjamin E. Van Kuiken ◽  
Justin T. Henthorn
Keyword(s):  
Oxidation State ◽  
Emission Spectroscopy ◽  
Model Complexes ◽  
X Ray

scholarly journals Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 116
Author(s):  
Gian Luca Chiarello ◽  
Ye Lu ◽  
Miren Agote-Arán ◽  
Riccardo Pellegrini ◽  
Davide Ferri
Keyword(s):  
Particle Size ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Oxidation State ◽  
Diffuse Reflectance ◽  
X Ray ◽  
Spectral Changes ◽  
Diffuse Reflectance Infrared ◽  
X Ray Absorption ◽  
Reversible Reduction

Infrared spectroscopy is typically not used to establish the oxidation state of metal-based catalysts. In this work, we show that the baseline of spectra collected in diffuse reflectance mode of a series of Pd/Al2O3 samples of increasing Pd content varies significantly and reversibly under alternate pulses of CO or H2 and O2. Moreover, these baseline changes are proportional to the Pd content in Pd/Al2O3 samples exhibiting comparable Pd particle size. Similar measurements by X-ray absorption spectroscopy on a different 2 wt.% Pd/Al2O3 confirm that the baseline changes reflect the reversible reduction-oxidation of Pd. Hence, we demonstrate that changes in oxidation state of metal-based catalysts can be determined using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and that this behavior is part of the spectral changes that are returned by experiments under operando conditions.

scholarly journals Influence of the Presence of Different Alkali Cations and the Amount of Fe(CN)6 Vacancies on CO2 Adsorption on Copper Hexacyanoferrates

Materials ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3371 ◽  
Author(s):  
Svensson ◽  
Grins ◽  
Eklöf ◽  
Eriksson ◽  
Wardecki ◽  
...  
Keyword(s):  
Thermogravimetric Analysis ◽  
Prussian Blue ◽  
Co2 Adsorption ◽  
X Ray Diffraction ◽  
Alkali Cations ◽  
Prussian Blue Analogue ◽  
X Ray ◽  
Infra Red ◽  
Adsorption Desorption ◽  
Adsorption Capability

The CO2 adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogravimetric analysis. Compositions of prepared phases were verified by energy-dispersive X-ray spectroscopy, infra-red spectroscopy and powder X-ray diffraction. The influence of different alkali cations in the cubic Fm3m structures was investigated for nominal compositions A2/3Cu[Fe(CN)6]2/3 with A = vacant, Li, Na, K, Rb, Cs. The Rb and Cs compounds show the highest CO2 adsorption per unit cell, 3.3 molecules of CO2 at 20 C and 1 bar, while in terms of mmol/g the Na compound exhibits the highest adsorption capability, 3.8 mmol/g at 20 C and 1 bar. The fastest adsorption/desorption is exhibited by the A-cation free compound and the Li compound. The influence of the amount of Fe(CN)6 vacancies were assessed by determining the CO2 adsorption capabilities of Cu[Fe(CN)6]1/2 (Fm3m symmetry, nominally 50% vacancies), KCu[Fe(CN)6]3/4 (Fm3m symmetry, nominally 25% vacancies), and CsCu[Fe(CN)6] (I-4m2 symmetry, nominally 0% vacancies). Higher adsorption was, as expected, shown on compounds with higher vacancy concentrations.

scholarly journals Magnetic spectroscopy of nanoparticulate greigite, Fe3S4

2017 ◽  
Vol 81 (4) ◽  
pp. 857-872 ◽  
Author(s):  
Richard A. D. Pattrick ◽  
Victoria S. Coker ◽  
Masood Akhtar ◽  
M. Azad Malik ◽  
Edward Lewis ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Oxidation State ◽  
Magnetic Circular Dichroism ◽  
Covalent Character ◽  
X Ray ◽  
Positive Feature ◽  
A Site ◽  
Intermediate Oxidation ◽  
X Ray Absorption ◽  
Ferrite Spinel

AbstractSynthesis of Ni and Zn substituted nano-greigite, Fe3S4, is achieved from single source diethyldithiocarbamato precursor compounds, producing particles typically 50–100 nm in diameter with plate-like pseudohexagonal morphologies. Up to 12 wt.% Ni is incorporated into the greigite structure, and there is evidence that Zn is also incorporated but Co is not substituted into the lattice. The FeL3X-ray absorption spectra for these materials have a narrow single peak at 707.7 eV and the resulting main X-ray magnetic circular dichroism (XMCD) has the same sign at 708.75 eV. All XMCD spectra also have a broad positive feature at 711 eV, a characteristic of covalent mixing. The greigite XMCD spectra contrast with the three clearly defined XMCD site specific peaks found in the ferrite spinel, magnetite. The FeL2,3X-ray absorption spectra and XMCD spectra of the greigite reflect and reveal the high conductivity of greigite and the very strong covalency of the Fe–S bonding. The electron hopping between Fe3+and Fe2+on octahedral sites results in an intermediate oxidation state of the Fe in the Ohsite of Fe2.5+producing an effective formula of [Fe3+↑]A-site[2Fe2.5+↓]B-siteS42–]. The NiL2,3X-ray absorption spectra and XMCD reveal substitution on the Ohsite with a strongly covalent character and an oxidation state <Ni1.5+in a representative formula [Fe3+↑]A[[(2 – x)Fe2.5+↓][Nix1.5+]]BS42–.

Synthesis and characterisation of transition metal substituted barium hollandite ceramics

2006 ◽  
Vol 932 ◽  
Author(s):  
Neil C. Hyatt ◽  
Martin C. Stennett ◽  
Steven G. Fiddy ◽  
Jayne S. Wellings ◽  
Sian S. Dutton ◽  
...  
Keyword(s):  
Transition Metal ◽  
Oxidation State ◽  
Powder Diffraction ◽  
Single Phase ◽  
Maximum Density ◽  
Processing Conditions ◽  
Metal Oxidation ◽  
Exafs Data ◽  
X Ray ◽  
Oxygen Atoms

ABSTRACTA range of transition metal bearing hollandite phases, formulated Ba1.2B1.2Ti6.8O16 (B2+ = Mg, Co, Ni, Zn, Mn) and Ba1.2B2.4Ti5.6O16 (B3+ = Al, Cr, Fe) were prepared using an alkoxide - nitrate route. X-ray powder diffraction demonstrated the synthesis of single phase materials for all compositions except B = Mn. The processing conditions required to produce > 95 % dense ceramics were determined for all compositions, except B = Mg for which the maximum density obtained was > 93 %. Analysis of transition metal K-edge XANES data confirmed the presence of the targeted transition metal oxidation state for all compositions except B = Mn, where the overall oxidation state was found to be Mn3+. The K-edge EXAFS data of Ba1.2B1.2Ti6.8O16 (B = Ni and Co) were successfully analysed using a crystallographic model of the hollandite structure, with six oxygen atoms present in the first co-ordination shell at a distance of ca. 2.02Å. Analysis of Fe K-edge EXAFS data of Ba1.2B2.4Ti5.4O16 revealed a reduced co-ordination shell of five oxygens at ca. 1.99Å.

scholarly journals SYNTHESIS OF ZnO-Аg NANOPARTICLES BY SOL-GEL METHOD

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Savka Janković ◽  
Dragana Milisavić ◽  
Tanja Okolić ◽  
Dijana Jelić
Keyword(s):  
Zno Nanoparticles ◽  
Wide Spectrum ◽  
Sol Gel ◽  
Synthesis Method ◽  
Material Surface ◽  
Characterization Methods ◽  
Gel Method ◽  
X Ray ◽  
Sol Gel Method ◽  
Doped Zno

Zinc oxide is a highly applicable semiconductor material. Wide applica-tion of this nanomaterial is connected to wide spectrum of energy band gap, high bond en-ergy, great thermal conductivity, but also with its non-toxicity, antibacterial activity, bio-compatibility and biodegradability characteristics. The aim of this paper is synthesis and characterization of silver doped ZnO nanoparticles (ZnO:Ag NP) using sol-gel method. Ob-tained samples of silver doped ZnO nanoparticles were characterized by following tech-niques: Fourier-transform infrared spectroscopy (FTIR), UV/VIS spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spec-troscopy (EDX). Efficiency of provided synthesis method was examined by FTIR spectros-copy. XRD determined the purity and crystallinity, and wurtzite structure of synthesized material. Surface morphology and the effect of doping were examined using SEM and EDX characterization methods. Results showed better conductivity after doping ZnO nanoparti-cles with silver. SEM micrographs showed ZnO:Ag NP in the form of nanorods with a par-ticle average size of 6 nm.

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