The surface chemistry of kaolinite. II. Catalysis of n-butane decomposition

1972 ◽  
Vol 25 (9) ◽  
pp. 1843 ◽  
Author(s):  
AS Buchanan ◽  
RC Oppenheim
Keyword(s):  
Catalytic Activity ◽  
Lone Pair ◽  
Acid Leaching ◽  
Hydroxyl Groups ◽  
Surface Oxygen ◽  
Hydrogen Atoms ◽  
Before And After ◽  
Hydrocarbon Reactions ◽  
Lone Pair Electrons ◽  
Oxygen Atoms

The catalytic activity of kaolinite before and after acid leaching for the decomposition of n-butane between 669 and 727 K has been compared with that of alumina natural and precipitated, and silica. The catalysis of hydrocarbon reactions on oxide surfaces appears to involve oxygen atoms which may be attached to the solid surface either physically adsorbed as the gas, as part of the lattice, or possibly as attached hydroxyl groups. Dehydrogenation of the hydrocarbon appears to be the first important step, suggesting that adsorption of the reactant involves interaction of the hydrogen atoms with lone pair electrons of surface oxygen atoms.

The molecular orbital theory of chemical valency. V. The structure of water and similar molecules

1950 ◽  
Vol 202 (1070) ◽  
pp. 323-336 ◽  
Keyword(s):  
Spatial Distribution ◽  
Equilibrium Configuration ◽  
Bond Angle ◽  
Lone Pair ◽  
Orbital Theory ◽  
Hydrogen Atoms ◽  
Molecular Formation ◽  
Major Factors ◽  
Lone Pair Electrons ◽  
Electrostatic Repulsions

The theory of molecular and equivalent orbitals developed in previous papers of this series is used to discuss the spatial distribution of lone-pair electrons in molecules such as H 2 O and NH 3 and the part they play in determining the equilibrium configuration. Previous treatments of H 2 O have assumed that the lone pairs are essentially unaltered by molecular formation. It is shown here, on the other hand, that they will be displaced so as to be mainly concentrated on the side of the O-nucleus remote from the hydrogen atoms. An important consequence of this is that the lone-pair electrons will make a contribution to the total dipole moment. Comparison of the experimentally observed moment with an approximate quantitative treatment suggests that, as a result of this, transfer of electrons from the hydrogen atoms to the oxygen does not occur to the extent that has previously been believed. The variation of the spatial distribution of the orbitals of H 2 O with changes of nuclear configuration is examined and it is shown that, in the equilibrium position, the electronic structure can be described approximately by two sets of two equivalent orbitals pointing in nearly tetrahedral directions. The dependence of total energy on bond angle is discussed and it is shown that electrostatic repulsions between the equivalent orbitals are major factors in determining the equilibrium configuration. Similar considerations apply to NH 3 .

scholarly journals STRUCTURE OF THE ZINC COMPLEX WITH CYCLOHEXYL AСETOACETATE

2020 ◽  
pp. 66-69
Author(s):  
O. Shtokvysh ◽  
L. Koval ◽  
V. Dyakonenko ◽  
V. Pekhnyo
Keyword(s):  
Ir Spectroscopy ◽  
Oxygen Atom ◽  
The Other ◽  
Axial Position ◽  
Hydroxyl Groups ◽  
Equatorial Position ◽  
Hydrogen Atoms ◽  
Bidentate Coordination ◽  
Terminal Ligand ◽  
Oxygen Atoms

Binuclear complex of Zn(II) with cyclohexyl acetoacetate was obtained and structurally characterized for the first time. According to structural data, the crystal system is triclinic, space group P-1; a = 7.6530(4), b = 12.2412(8), c = 12.9102(9) Å; α = 90.198(5), β = 101.071(5), γ = 96.937(5) deg. The molecular structure corresponds to the formula [Zn2(C10H15O3)4(C2H5OH)2]. The complex is located in a special position to the symmetry center of the unit cell. The coordination polyhedrons of the Zn atoms are the same distorted octahedrons formed by six oxygen atoms. Each formed by 4 oxygen atoms in the equatorial position, which belong to three ligand molecules: terminal ligand (2 oxygen atoms) and bridged ligand (1 oxygen atom) which chelate the zinc atom of the named polyhedron and 1 oxygen atom belong to a bridged ligand that chelates the other nucleus and monodentantly coordinated to mentioned one. Two oxygen atoms occupy an axial position, one of which belongs to the terminal ligand, mentioned above and the other to the coordinated ethanol molecule. The bond between the complex nuclei is stabilized by two hydrogen bonds formed by the hydrogen atoms from hydroxyl groups of ethanol molecules and the enol oxygen atoms of the terminal ligands of the other nucleus. The compound was also characterized by IR-spectroscopy, characteristic bands (сm-1) are: ν(C–H) - 2936, 2860, ν(C=O) & ν(C=C) – 1612, ν(C=O) + δ(C–H) – 1532, ν(C=C) & ν(C-CH3)– 1252, δ(C–H) – 1172, π(C–H) – 784, ν(M–O) – 456, 416. IR spectroscopy data confirm the bidentate coordination of cyclohexyl acetoacetate to zinc atoms in deprotonated form with the formation of chelated metallocycles. The structure of the complex is similar to the structures of cobalt and nickel complexes with cyclohexyl acetoacetate. Analysis of XRD-data (which are supplemented with this work) for Co(II), Ni(II) and Zn(II) complexes with acetoacetic acid esters shows that their structure, in particular the number of metal centers in the structures, regardless of the nature of the central atom or the alcohol fragment, but determined the presence of components capable of complementing the coordination sphere of the metal in reaction media.

Conformational equilibria in some cyclic imines: NH and CH stretching vibrations and the axial lone pair

1970 ◽  
Vol 48 (20) ◽  
pp. 3236-3248 ◽  
Author(s):  
P. J. Krueger ◽  
J. Jan
Keyword(s):  
Lone Pair ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Trans Orientation ◽  
Methyl Substitution ◽  
Lone Pair Orbital ◽  
Conformational Equilibria ◽  
Solvent Environment ◽  
Stretching Vibrations ◽  
Lone Pair Electrons

The fundamental NH and CH stretching vibrations of a number of cyclic imines have been examined in dilute CC14 solution. A trans orientation of the N lone pair orbital and one or more hydrogen atoms on adjacent carbons lowers the relevant vCH ("Bohlmann" bands) and raises vNH reflecting an increase in the s-character of the CH bond(s), consistent with a partial delocalization of the lone pair electrons into the CN bond. Conformations in which this interaction occurs are thermodynamically favored, and the ΔH values for the lone pair axial–equatorial equilibrium in piperidine, pyrrolidine, and indolene are estimated to be 0.4, 0.2, and 0.1 kcal/mole, respectively, in dilute CCl4 solution.The effects of hetero ring size, N-substitution, α-methyl substitution, and the solvent environment are investigated.

A theoretical approach to the energetic stability and geometry of hydrogen and oxygen terminated diamond (100) surfaces

2005 ◽  
Vol 890 ◽  
Author(s):  
Daniel Petrini ◽  
Karin Larsson
Keyword(s):  
Thermodynamic Stability ◽  
Adsorption Energy ◽  
Theoretical Approach ◽  
Surface Coverage ◽  
Hydroxyl Groups ◽  
Hydrogen Atoms ◽  
Energetic Stability ◽  
Oxygen Coverage ◽  
Oxygen Atoms

ABSTRACTThe thermodynamic stability of diamond (100) surfaces as a function of degree of hydrogen and oxygen-related termination coverage has been theoretically studied using DFT techniques. The results show that an exchange of the hydrogen atoms with hydroxyl groups is disfavored, whereas a corresponding exchange with oxygen atoms (in the ketone or ether position) is energetically preferred. The adsorption of up to about 50 % oxygen coverage (ether position) is, however, largely disfavored compared to a fully hydrogen-terminated surface. However, this oxygen termination will be energetically improved as the coverage increases above the 50 % level. The adsorption energy per terminating species (at 100% surface coverage) is −4.13 eV, −4.30 eV, −5.95 eV and 6.21 eV for H, OH, O(ketone) and O(ether) species, respectively.

The polymerization of ethylene on chromium oxide catalysts II. Infrared studies

1972 ◽  
Vol 329 (1579) ◽  
pp. 375-390 ◽  
Keyword(s):  
Catalytic Activity ◽  
Adsorbed Water ◽  
Oxidation Products ◽  
Polymerization Reaction ◽  
Oxide Surface ◽  
Hydroxyl Groups ◽  
Hydrogen Atoms ◽  
Chromium Vi ◽  
Infrared Studies ◽  
Chromium Oxide Catalysts

Ethylene reduces silica supported chromium(VI) oxide catalyst at 300 °C and adsorbs as ethyl groups by a self-hydrogenation mechanism. No exchange of hydrogen atoms between ethylene and the hydroxyl groups in the oxide surface occurs. Ethyl groups are adsorbed on chromium atoms in both high (probably + 5) and low (probably + 3) oxidation states and are partially desorbed, particularly from the former, by evacuation at 300 °C. The adsorption of ethylene confers catalytic activity for the polymerization of ethylene at 50 °C on chromium(v) atoms but chromium(III) atoms on which there are adsorbed ethyl groups are inactive. The catalytic activity of the high oxidation state sites from which ethyl groups desorbed during evacuation at 300 °C depends upon the form of the adsorption isotherm of ethylene on the sites at 50 °C. The adsorption of ethylene as ethyl groups constitutes the initiation step in the polymerization reaction. The products from the oxidation of ethylene caused by contact with catalyst appear in part as adsorbed water, carboxylate, carbonate, and carbonyl species. The catalytic activity of the oxide is poisoned by the presence of the adsorbed oxidation products but is enhanced by evacuation at 300 °C which causes their desorption.

scholarly journals Synthesis and Surface Characterization ofγ-MnO2Nanostructures

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Chengxiang Liu ◽  
Jing Wang ◽  
Jiarui Tian ◽  
Lan Xiang
Keyword(s):  
Surface Properties ◽  
Electron Density ◽  
Surface Potential ◽  
Surface Characterization ◽  
Hydroxyl Groups ◽  
Surface Oxygen ◽  
Initial Ph ◽  
Oxygen Atoms

A facile method was developed to synthesizeγ-MnO2with different structures and surface properties in this paper.γ-MnO2was prepared by oxidation of MnSO4with Na2S2O8at90°C for 2.0 h.γ-MnO2formed at initial pH 1.0 (M1) and 8.5 (M2) was composed of MnO1.93·0.23H2O and MnO1.96·0.18H2O, respectively. The higher ratio of pyrolusite in M2 (Pr=43.90%) than that in M1 (Pr=24.86%) indicated that compared with M1, M2 would absorb more protons since the planar oxygen atoms in pyrolusite were incompletely coordinated and liable to absorb the protons. Meanwhile, the higher oxidation valence of Mn in M2 than that in M1 revealed that the Mn atoms in M2 were more liable to draw the electron density from the surface oxygen atoms in hydroxyl groups. The structural and compositional differences between M1 and M2 were the major reasons why M2 possessed a higher surface potential and a weaker ability to absorb Zn2+ions.

119Sn, 13C and 1H NMR Spectra of Tris(1-butyl)stannyl D-Glucuronate

1997 ◽  
Vol 62 (8) ◽  
pp. 1169-1176 ◽  
Author(s):  
Antonín Lyčka ◽  
Jaroslav Holeček ◽  
David Micák
Keyword(s):  
Chemical Shift ◽  
Carbonyl Group ◽  
1H Nmr ◽  
Equatorial Plane ◽  
Title Compound ◽  
Nmr Spectra ◽  
Hydroxyl Groups ◽  
Carboxylic Group ◽  
H Nmr ◽  
Oxygen Atoms

The 119Sn, 13C and 1H NMR spectra of tris(1-butyl)stannyl D-glucuronate have been measured in hexadeuteriodimethyl sulfoxide, tetradeuteriomethanol and deuteriochloroform. The chemical shift values have been assigned unambiguously with the help of H,H-COSY, TOCSY, H,C-COSY and 1H-13C HMQC-RELAY. From the analysis of parameters of 119Sn, 13C and 1H NMR spectra of the title compound and their comparison with the corresponding spectra of tris(1-butyl)stannyl acetate and other carboxylates it follows that in solutions of non-coordinating solvents (deuteriochloroform) the title compound is present in the form of more or less isolated individual molecules with pseudotetrahedral environment around the central tin atom and with monodentately bound carboxylic group. The interaction of tin atom with oxygen atoms of carbonyl group and hydroxyl groups of the saccharide residue - if they are present at all - are very weak. In solutions in coordinating solvents (hexadeuteriodimethyl sulfoxide or tetradeuteriomethanol), the title compound forms complexes with one molecule of the solvent. Particles of these complexes have a shape of trigonal bipyramid with the 1-butyl substituents in equatorial plane and the oxygen atoms of monodentate carboxylic group and coordinating solvent in axial positions.

Effect of delocalization of nonbonding electron density on the stability of the M–Ccarbene bond in main group metal-imidazol-2-ylidene complexes: a computational and structural database study

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Samuel Tetteh ◽  
Albert Ofori
Keyword(s):  
Electron Density ◽  
Lone Pair ◽  
Main Group ◽  
Binding Energies ◽  
Electrostatic Model ◽  
Group Metal ◽  
Main Group Metal ◽  
Structural Database ◽  
The Stability ◽  
Lone Pair Electrons

Abstract The M–Ccarbene bond in metal (M) complexes involving the imidazol-2-ylidene (Im) ligand has largely been described using the σ-donor only model with donation of σ electrons from the sp-hybridized orbital of the carbene carbon into vacant orbitals on the metal centre. Analyses of the M–Ccarbene bond in a series of group IA, IIA and IIIA main group metal complexes show that the M-Im interactions are mostly electrostatic with the M–Ccarbene bond distances greater than the sum of the respective covalent radii. Estimation of the binding energies of a series of metal hydride/fluoride/chloride imidazol-2-ylidene complexes revealed that the stability of the M–Ccarbene bond in these complexes is not always commensurate with the σ-only electrostatic model. Further natural bond orbital (NBO) analyses at the DFT/B3LYP level of theory revealed substantial covalency in the M–Ccarbene bond with minor delocalization of electron density from the lone pair electrons on the halide ligands into antibonding molecular orbitals on the Im ligand. Calculation of the thermodynamic stability of the M–Ccarbene bond showed that these interactions are mostly endothermic in the gas phase with reduced entropies giving an overall ΔG > 0.

scholarly journals Long-term stability in γ-CsPbI3 perovskite via an ultraviolet-curable polymer network

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Nam-Kwang Cho ◽  
Hyun-Jae Na ◽  
Jeeyoung Yoo ◽  
Youn Sang Kim
Keyword(s):  
Polymer Network ◽  
Lone Pair ◽  
Ambient Conditions ◽  
Absorption Properties ◽  
Term Stability ◽  
Long Term Stability ◽  
Ultraviolet Curable ◽  
Oxygen Lone Pair ◽  
Lone Pair Electrons

AbstractBlack-colored (α, γ-phase) CsPbI3 perovskites have a small bandgap and excellent absorption properties in the visible light regime, making them attractive for solar cells. However, their long-term stability in ambient conditions is limited. Here, we demonstrate a strategy to improve structural and electrical long-term stability in γ-CsPbI3 by the use of an ultraviolet-curable polyethylene glycol dimethacrylate (PEGDMA) polymer network. Oxygen lone pair electrons from the PEGDMA are found to capture Cs+ and Pb2+ cations, improving crystal growth of γ-CsPbI3 around PEGDMA. In addition, the PEGDMA polymer network strongly contributes to maintaining the black phase of γ-CsPbI3 for more than 35 days in air, and an optimized perovskite film retained ~90% of its initial electrical properties under red, green, and blue light irradiation.

scholarly journals High catalytic activity for formaldehyde oxidation of an interconnected network structure composed of δ-MnO2 nanosheets and γ-MnOOH nanowires

2020 ◽  
Vol 8 (4) ◽  
pp. 429-439
Author(s):  
Ying Tao ◽  
Rong Li ◽  
Ai-Bin Huang ◽  
Yi-Ning Ma ◽  
Shi-Dong Ji ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Network Structure ◽  
Manganese Oxides ◽  
Active Oxygen Species ◽  
Low Cost ◽  
High Dispersion ◽  
Hydroxyl Groups ◽  
High Catalytic Activity ◽  
Interconnected Network ◽  
Surface Hydroxyl

AbstractAmong the transition metal oxide catalysts, manganese oxides have great potential for formaldehyde (HCHO) oxidation at ambient temperature because of their high activity, nontoxicity, low cost, and polybasic morphologies. In this work, a MnO2-based catalyst (M-MnO2) with an interconnected network structure was successfully synthesized by a one-step hydrothermal method. The M-MnO2 catalyst was composed of the main catalytic agent, δ-MnO2 nanosheets, dispersed in a nonactive framework material of γ-MnOOH nanowires. The catalytic activity of M-MnO2 for HCHO oxidation at room temperature was much higher than that of the pure δ-MnO2 nanosheets. This is attributed to the special interconnected network structure. The special interconnected network structure has high dispersion and specific surface area, which can provide more surface active oxygen species and higher surface hydroxyl groups to realize rapid decomposition of HCHO.

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