scholarly journals M(II)Al4 Type Layered Double Hydroxides—Preparation Using Mechanochemical Route, Structural Characterization and Catalytic Application

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4880
Author(s):  
Márton Szabados ◽  
Adél Anna Ádám ◽  
Zsolt Kása ◽  
Kornélia Baán ◽  
Róbert Mucsi ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Infrared Spectroscopy ◽  
Layered Double Hydroxides ◽  
Diffuse Reflectance ◽  
Diffuse Reflectance Spectroscopy ◽  
Copper Nitrate ◽  
Oxidation Reactions ◽  
Temperature Oxidation ◽  
Diffuse Reflectance Infrared ◽  
Double Hydroxides

The synthesis of the copper-poor and aluminum-rich layered double hydroxides (LDHs) of the CuAl4 type was optimized in detail in this work, by applying an intense mechanochemical treatment to activate the gibbsite starting reagent. The phase-pure forms of these LDHs were prepared for the first time; using copper nitrate and perchlorate salts during the syntheses turned out to be the key to avoiding the formation of copper hydroxide sideproducts. Based on the use of the optimized syntheses parameters, the preparation of layered triple and multiple hydroxides was also attempted using Ni(II), Co(II), Zn(II) and even Mg(II) ions. These studies let us identify the relative positions of the incorporating cations in the well-known selectivity series as Ni2+ >> Cu2+ >> Zn2+ > Co2+ >> Mg2+. The solids formed were characterized by using powder X-ray diffractometry, UV–Vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. The catalytic potential of the samples was investigated in carbon monoxide oxidation reactions at atmospheric pressure, supported by an in situ diffuse reflectance infrared spectroscopy probe. All solids proved to be active and the combination of the nickel and cobalt incorporation (which resulted in a NiCoAl8 layered triple hydroxide) brought outstanding benefits regarding low-temperature oxidation and increased carbon monoxide conversion values.

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.

Figures of Merit for a Diffuse Reflectance Accessory Using an On-Axis Ellipsoidal Collecting Mirror

1988 ◽  
Vol 42 (3) ◽  
pp. 428-433 ◽  
Author(s):  
E. H. Korte
Keyword(s):  
Infrared Spectroscopy ◽  
Noise Level ◽  
Diffuse Reflectance ◽  
Field Of View ◽  
Figures Of Merit ◽  
Size Dependent ◽  
Diffuse Reflectance Infrared Spectroscopy ◽  
Diffuse Reflectance Infrared

The attainable efficiency of an accessory for diffuse reflectance infrared spectroscopy where both the irradiation and detection optics are located on the same side of the sample is analyzed, the size-dependent noise level of the detector being taken into account. The resulting figures of merit are found to reach up to more than 0.3, when standard detectors of 60° field-of-view are considered.

scholarly journals Clay intercalated Cu(II) amino acid complexes: synthesis, spectroscopy and catalysis

Clay Minerals ◽  
1996 ◽  
Vol 31 (4) ◽  
pp. 491-500 ◽  
Author(s):  
L. Fu ◽  
B. M. Weckhuysen ◽  
A. A. Verberckmoes ◽  
R. A. Schoonheydt
Keyword(s):  
Amino Acid ◽  
Diffuse Reflectance ◽  
Diffuse Reflectance Spectroscopy ◽  
The Novel ◽  
Oxidation Reactions ◽  
Axially Symmetric ◽  
X Ray Diffraction ◽  
X Ray ◽  
Spin Resonance ◽  
Synthesized Materials

AbstractComplexes of Cu(lysine)2+2 and Cu(histidine)2+2 have been intercalated between the layers of saponite clays by a simple cation exchange procedure from aqueous solutions of preformed Cu(amino acid)2-complexes. Successful immobilization was obtained with an amino acid: Cu2+ ratio of 5, and a pH of 10 and 7.3 for lysine and histidine, respectively. The synthesized materials were investigated as powders and as thin films by electron spin resonance (ESR), diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD). The light blue clays are characterized by an axially symmetric ESR spectrum with A//= 192 G, g//= 2.23 and g⊥ = 2.07, and a d-d absorption band around 600 nm, due to the intercalated planar Cu2+-complexes. Ammonia interacts reversibly with these intercalated complexes, suggesting the presence of a free coordination site. The novel synthesized materials are active in various oxidation reactions with t-butyl hydroperoxide as oxidant.

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