scholarly journals Tracing the acid-base catalytic properties of MON2O mixed oxides (M = Be, Mg, Ca; N = Li, Na, K) by theoretical calculations

2021 ◽  
Vol 27 (7) ◽  
Author(s):  
Dawid Faron ◽  
Piotr Skurski ◽  
Iwona Anusiewicz
Keyword(s):  
Gas Phase ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Theoretical Calculations ◽  
Lewis Acidity ◽  
Ab Initio Methods ◽  
Free Energies ◽  
Acid Base ◽  
The Stability ◽  
Fragmentation Processes

AbstractThe stability and acid-base properties of MON2O mixed oxides (where M = Be, Mg, Ca; N = Li, Na, K) are studied by using ab initio methods. It is demonstrated that (i) the basicity of such designed systems evaluated by estimation of electronic proton affinity and gas-phase basicity (defined as the electronic and Gibbs free energies of deprotonation processes for [MON2O]H+) were found significant (in the ranges of 272–333 and 260–322 kcal/mol, respectively); (ii) in each series of MOLi2O/MONa2O/MOK2O, the basicity increases with an increase of the atomic number of alkali metal involved; (ii) the Lewis acidity of the corresponding [MON2O]H+ determined with respect to hydride anion (assessed as the electronic and Gibbs free energies of H− detachment processes for [MON2O]H2) decreases as the basicity of the corresponding oxide increases. The thermodynamic stability of all [MON2O]H2 systems is confirmed by estimating the Gibbs free energies for the fragmentation processes yielding either H2 or H2O.

scholarly journals Tracing The Acid-Base Catalytic Properties Of MON2O Mixed Oxides (M=Be, Mg, Ca; N=Li, Na, K) By Theoretical Calculations

2021 ◽  
Author(s):  
Dawid Faron ◽  
Piotr Skurski ◽  
Iwona Anusiewicz
Keyword(s):  
Alkali Metal ◽  
Gas Phase ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Theoretical Calculations ◽  
Lewis Acidity ◽  
Free Energies ◽  
Acid Base ◽  
The Stability ◽  
Fragmentation Processes

Abstract The stability and acid-base properties of MON2O mixed oxides (where M = Be, Mg, Ca; N = Li, Na, K) are studied by using ab initio methods. It is demonstrated that (i) the basicity of such designed systems evaluated by estimation of electronic proton affinity and gas-phase basicity (defined as the electronic and Gibbs free energies of deprotonation processes for [MON2O]H+) were found significant (in the ranges of 272–333 kcal/mol and 260–322 kcal/mol, respectively); (ii) in each series of MOLi2O/MONa2O/MOK2O the basicity increases with an increase of the atomic number of alkali metal involved; (ii) the Lewis-acidity of the corresponding [MON2O]H+ determined with respect to hydride anion (assessed as the electronic and Gibbs free energies of H− detachment processes for [MON2O]H2) decreases as the basicity of the corresponding oxide increases. The thermodynamic stability of all [MON2O]H2 systems is confirmed by estimating the Gibbs free energies for the fragmentation processes yielding either H2 or H2O.

Electron Donating, Acid-Base and Catalytic Properties of Perovskite-Type Mixed Oxides of Rare Earths

1995 ◽  
Vol 60 (6) ◽  
pp. 977-982
Author(s):  
S. Sugunan ◽  
V. Meera
Keyword(s):  
Catalytic Activity ◽  
Electron Donor ◽  
Rare Earths ◽  
Electron Affinity ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Surface Acidity ◽  
Electron Acceptors ◽  
Acid Base ◽  
Perovskite Type

The electron donor properties of perovskite-type mixed oxides (LaFeO3, PrFeO3, SmFeO3, LaCoO3, PrCoO3, SmCoO3, LaNiO3, PrNiO3 and SmNiO3) were studied based on the adsorption of electron acceptors exhibiting different electron affinity viz. 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro-1,4-benzoquinone, p-dinitrobenzene, and m-dinitrobenzene. The surface acidity/basicity of the oxides was determined using a set of Hammett indicators. The data were correlated with the catalytic activity of the oxides for the reduction of cyclohexanone with 2-propanol.

Mindo-Forces Study on the Keto-Enol Tautomerism of α-Substituted Acetaldehydes XCH2CH=O (X = H, F, Oh, Cn, NH2, NO2, CH3, CF3, OCH3): Comparison with Acetyl Derivatives

2004 ◽  
Vol 59 (12) ◽  
pp. 980-986
Author(s):  
Wasim F. Al-Halasah ◽  
Salim M. Khalil
Keyword(s):  
Theoretical Calculations ◽  
Geometry Optimization ◽  
Substituent Effects ◽  
Geometrical Parameters ◽  
Free Energies ◽  
Electron Densities ◽  
The Stability ◽  
Complete Geometry Optimization

MINDO-Forces calculations with complete geometry optimization have been performed on α- substituted acetaldehydes XCH2CH=O and their enols (X = H, F, OH, CN, NH2, NO2, CH3, CF3, OCH3). All substituents were found to decrease the stability of the acetaldehyde and mostly in the case of electron withdrawing capacity (e. g NO2 and CF3). This agrees with theoretical calculations, except in the case of F. The substituent effects on the stabilities in this study are compared with results obtained from our previous theoretical calculations on acetyl derivatives. Geometrical parameters, electron densities, and Gibbs free energies are reported.

scholarly journals Synthesis of Chalcone Using LDH/Graphene Nanocatalysts of Different Compositions

2019 ◽  
Vol 3 (1) ◽  
pp. 29 ◽  
Author(s):  
Mayra Álvarez ◽  
Dana Crivoi ◽  
Francesc Medina ◽  
Didier Tichit
Keyword(s):  
Active Sites ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Condensation Reaction ◽  
Nanocomposite Materials ◽  
Acid Base ◽  
Basic Sites ◽  
Base Catalysts ◽  
Reduced Graphene ◽  
Double Hydroxides

Layered double hydroxides (LDH) or their derived mixed oxides present marked acid-base properties useful in catalysis, but they are generally agglomerated, inducing weak accessibility to the active sites. In the search for improving dispersion and accessibility of the active sites and for controlling the hydrophilic/hydrophobic balance in the catalysts, nanocomposite materials appear among the most attractive. In this study, a series of nanocomposites composed of LDH and reduced graphene oxide (rGO), were successfully obtained by direct coprecipitation and investigated as base catalysts for the Claisen–Schmidt condensation reaction between acetophenone and benzaldehyde. After activation, the LDH-rGO nanocomposites exhibited improved catalytic properties compared to bare LDH. Moreover, they reveal great versatility to tune the selectivity through their composition and the nature or the absence of solvent. This is due to the enhanced basicity of the nanocomposites as the LDH content increases which is assigned to the higher dispersion of the nanoplatelets in comparison to bulk LDH. Lewis-type basic sites of higher strength and accessibility are thus created. The nature of the solvent mainly acts through its acidity able to poison the basic sites of the nanocatalysts.

What are the Molecules of Which the Samples of Metal Alkoxides do Really Consist ?

1994 ◽  
Vol 346 ◽  
Author(s):  
N.Ya. Turova ◽  
N.I. Kozlova ◽  
E.P. Turevskaya ◽  
T.V. Rogova ◽  
V.G. Kessler
Keyword(s):  
Gas Phase ◽  
Aromatic Hydrocarbons ◽  
Mass Spectra ◽  
Mixed Oxides ◽  
Metal Alkoxides ◽  
Boiling Points ◽  
Thermal Constants ◽  
Molecular Masses ◽  
Molecular Complexity ◽  
The Stability

ABSTRACTOn the basis of consideration of the properties of AI, In, Ln, Ti, Zr, Hf, NbO3+, MoO4+, WO4+, MoO22+ MO22+, Fe, Co, Ni alkoxide derivatives the main regularities in poly- and oligomerization properties have been deduced:1) The molecular complexity increases in time (aging) and on action of alcohols. This process is followed by the increase in the melting and boiling points, decrease in solubility in ROH and weakening of colour. In the mass-spectra - in connection with the temperature of transition into the gas phase - increases the stability of products with lower molecular masses. 2) oligomerization occurs on dissolution in aromatic hydrocarbons or on a short thermal treatment (melting, distillation). The oligomerization products possess lower thermal constants, higher solubility in ROH and more intense colour. Their mass- spectra are containing the fragments of higher masses corresponding to oligomers existing apparently also in the condensed phase.The mastering of these regularities permits the monitoring of molecular composition and thus physicochemical properties of the samples which are of importance for their technological application.The presence of oxoalkoxides in the “M(OR)n” samples should be taken into consideration on the preparation of solutions used in the synthesis of powders and films of pure simple and mixed oxides.

scholarly journals Theoretical Calculations for the Acidity of Cyanopolyynes HC2n+1N (n = 0–5) in Gas and Aqueous Phases Using Ab initio Methods

2019 ◽  
Vol 7 (1) ◽  
pp. 27
Author(s):  
Hassan H. Abdallah
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Dust Cloud ◽  
Basis Set ◽  
Ab Initio Methods ◽  
Functional Theory ◽  
Moller Plesset ◽  
Cold Dust

Cyanopolyynes have been found in the interstellar medium, cold dust cloud Taurus Molecular Cloud-1, and the Titan’s atmosphere. Theoretical calculations are carried out to predict gas and aqueous phase acidities of a series of cyanopolyynes acids. Two levels of theory were used in this study, with the combination of density functional theory, and Møller–Plesset perturbation (MP2) theory, MP2 methods with two types of basis set, namely, Pople’s 6–311++g (d, p) basis set and Dunning’s aug-cc-pVTZ basis set. The calculations of these molecules reveal that pKa values varying from 12.25 to 17.25 and indicate that the acidity of these molecules in aqueous phase increases whereas the acidity in gas phase decreases with an increasing chain length of these acids.

Microstructure and reactivity of small metal particles: The role of Ce additives

1992 ◽  
Vol 50 (1) ◽  
pp. 318-319
Author(s):  
L.D. Schmidt ◽  
K. R. Krause ◽  
J. M. Schwartz ◽  
X. Chu
Keyword(s):  
Atmospheric Pressure ◽  
Noble Metals ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Chemical Shifts ◽  
Catalytic Converter ◽  
Structural Evolution ◽  
Single Particles ◽  
Small Metal Particles

The evolution of microstructures of 10- to 100-Å diameter particles of Rh and Pt on SiO2 and Al2O3 following treatment in reducing, oxidizing, and reacting conditions have been characterized by TEM. We are able to transfer particles repeatedly between microscope and a reactor furnace so that the structural evolution of single particles can be examined following treatments in gases at atmospheric pressure. We are especially interested in the role of Ce additives on noble metals such as Pt and Rh. These systems are crucial in the automotive catalytic converter, and rare earths can significantly modify catalytic properties in many reactions. In particular, we are concerned with the oxidation state of Ce and its role in formation of mixed oxides with metals or with the support. For this we employ EELS in TEM, a technique uniquely suited to detect chemical shifts with ∼30Å resolution.

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

2005 ◽  
Vol 70 (11) ◽  
pp. 1769-1786 ◽  
Author(s):  
Luc A. Vannier ◽  
Chunxiang Yao ◽  
František Tureček
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Computational Study ◽  
Hydrogen Atom Abstraction ◽  
Oh Radical ◽  
Free Energies ◽  
Intramolecular Hydrogen ◽  
Solvation Free Energies ◽  
Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

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