scholarly journals Base Catalysis of Sodium Salts of [Ta6−xNbxO19]8− Mixed-Oxide Clusters

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1267
Author(s):  
Soichi Kikkawa ◽  
Mio Tsukada ◽  
Kanako Shibata ◽  
Yu Fujiki ◽  
Kazuki Shibusawa ◽  
...  
Keyword(s):  
Metal Oxide ◽  
Mixed Oxide ◽  
Base Catalysis ◽  
Solid Base ◽  
High Symmetry ◽  
Sodium Salts ◽  
X Ray ◽  
Metal Oxide Clusters ◽  
Anisotropic Expansion ◽  
Nbo Charges

The solid base catalysis of sodium salts of Lindqvist-type metal oxide clusters was investigated using a Knoevenagel condensation reaction. We successfully synthesized the sodium salts of Ta and Nb mixed-oxide clusters Na8−nHn[(Ta6−xNbx)O19]·15H2O (Na-Ta6−xNbx, n = 0, 1, x = 0–6) and found them to exhibit activity for proton abstraction from nitrile substrates with a pKa value of 23.8, which is comparable to that of the conventional solid base MgO. The Ta-rich Na-Ta6 and Na-Ta4Nb2 exhibited high activity among Ta and Nb mixed-oxide clusters. Synchrotron X-ray diffraction (SXRD) measurements, Fourier-transform infrared (FT-IR) spectroscopy, and X-ray absorption spectroscopy (XAS) revealed the structure of Na-Ta6−xNbx: (1) The crystal structure changed from Na7H[M6O19]·15H2O to Na8[M6O19]·15H2O (M = Ta or Nb) by the anisotropic expansion of the unit cell with an increase in Ta content; (2) Highly symmetrical Lindqvist [Ta6−xNbxO19]8− was generated in Na-Ta4Nb2 and Na-Ta6 because of the symmetrical association of Na+ ions with [Ta6−xNbxO19]8− in the structure. DFT calculation revealed that the Lindqvist structures with high symmetry have large NBO charges on surface oxygen species, which are strongly related to base catalytic activity, whereas the composition hardly affects the NBO charges. The above results showed that the Brønsted base catalysis was sensitive to the symmetry of the Lindqvist [Ta6−xNbxO19]8− structure. These findings contribute to the design of solid base catalysts composed of anionic metal oxide clusters with alkaline-metal cations.

The Interplay of Open-Shell Spin-Coupling and Jahn-Teller Distortion in Benzene Radical Cation Probed by X-ray Spectroscopy

2020 ◽  
Author(s):  
Marta L. Vidal ◽  
Michael Epshtein ◽  
Valeriu Scutelnic ◽  
Zheyue Yang ◽  
Tian Xue ◽  
...  
Keyword(s):  
High Harmonic ◽  
Open Shell ◽  
Spin Coupling ◽  
High Symmetry ◽  
Teller Distortion ◽  
Spectral Window ◽  
X Ray ◽  
Jahn Teller ◽  
X Ray Absorption ◽  
Jahn Teller Distortion

We report a theoretical investigation and elucidation of the x-ray absorption spectra of neutral benzene and of the benzene cation. The generation of the cation by multiphoton ultraviolet (UV) ionization as well as the measurement of<br>the carbon K-edge spectra of both species using a table-top high-harmonic generation (HHG) source are described in the companion experimental paper [M. Epshtein et al., J. Phys.<br>Chem. A., submitted. Available on ChemRxiv]. We show that the 1sC -> pi transition serves as a sensitive signature of the transient cation formation, as it occurs outside of the spectral window of the parent neutral species. Moreover, the presence<br>of the unpaired (spectator) electron in the pi-subshell of the cation and the high symmetry of the system result in significant differences relative to neutral benzene in the spectral features associated with the 1sC ->pi* transitions. High-level calculations using equation-of-motion coupled-cluster theory provide the interpretation of the experimental spectra and insight into the electronic structure of benzene and its cation.<br>The prominent split structure of the 1sC -> pi* band of the cation is attributed to the interplay between the coupling of the core -> pi* excitation with the unpaired electron<br>in the pi-subshell and the Jahn-Teller distortion. The calculations attribute most of<br>the splitting (~1-1.2 eV) to the spin coupling, which is visible already at the Franck-Condon structure, and estimate the additional splitting due to structural relaxation to<br>be around ~0.1-0.2 eV. These results suggest that x-ray absorption with increased resolution might be able to disentangle electronic and structural aspects of the Jahn-Teller<br>effect in benzene cation.<br>

Calcium Methoxide Synthesis from Quick Lime Using as Solid Catalyst in Refined Palm Oil Biodiesel Production

2013 ◽  
Vol 834-836 ◽  
pp. 550-554 ◽  
Author(s):  
Warakom Suwanthai ◽  
Vittaya Punsuvon ◽  
Pilanee Vaithanomsat
Keyword(s):  
Palm Oil ◽  
Acid Methyl Ester ◽  
Biodiesel Production ◽  
Molar Ratio ◽  
Catalyst Loading ◽  
Solid Catalyst ◽  
Solid Base ◽  
Quick Lime ◽  
X Ray ◽  
Refined Palm Oil

In this research, calcium methoxide was synthesized as solid base catalyst from quick lime for biodiesel production. The catalyst was further characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), attenuated total reflection fourier transform (ATR-FTIR) and Energy-dispersive X-ray spectroscopies (EDX) to evaluate its performance. The transesterification of refined palm oil using calcium methoxide and the process parameters affecting the fatty acid methyl ester (FAME) content such as catalyst concentration, methanol:oil molar ratio and reaction time were investigated. The results showed that the FAME content at 97% was achieved within 3 h using 3 %wt catalyst loading, 12:1 methanol:oil molar ratio and 65 °C reaction temperature. The result of FAME suggested calcium methoxide was the promising solid catalyst for substitution of the conventional liquid catalyst.

Temperature-dependent synchrotron X-ray diffraction, pair distribution function and susceptibility study on the layered compound CrTe3

2018 ◽  
Vol 233 (6) ◽  
pp. 361-370 ◽  
Author(s):  
Anna-Lena Hansen ◽  
Bastian Dietl ◽  
Martin Etter ◽  
Reinhard K. Kremer ◽  
David C. Johnson ◽  
...  
Keyword(s):  
Distribution Function ◽  
Pair Distribution Function ◽  
Exchange Interactions ◽  
Structural Distortion ◽  
Layered Compound ◽  
Minor Amount ◽  
Zero Field ◽  
X Ray Diffraction ◽  
X Ray ◽  
Anisotropic Expansion

Abstract Results of combined synchrotron X-ray diffraction and pair distribution function experiments performed on the layered compound CrTe3 provide evidence for a short range structural distortion of one of the two crystallographically independent CrTe6 octahedra. The distortion is caused by higher mobility of one crystallographically distinct Te ion, leading to an unusual large Debye Waller factor. In situ high temperature X-ray diffraction investigations show an initial crystallization of a minor amount of elemental Te followed by decomposition of CrTe3 into Cr5Te8 and Te. Additional experiments provide evidence that the Te impurity (<1%) cannot be avoided. Analyses of structural changes in the temperature range 100–754 K show a pronounced anisotropic expansion of the lattice parameters. The differing behavior of the crystal axes is explained on the basis of structural distortions of the Cr4Te16 structural building units. An abrupt distortion of the structure occurs at T≈250 K, which then remains nearly constant down to 100 K. The structural distortion affects the spin exchange interactions between Cr3+ cations. A significant splitting between field-cooled (fc) and zero-field-cooled (zfc) magnetic susceptibility is observed below about 200 K. Applying a small external magnetic field results in a substantial spontaneous magnetization, reminiscent of ferro- or ferrimagnet exchange interactions below ~240 K. A Debye temperature of ~150 K was extracted from heat capacity measurements.

Understanding the mechanism of photochromism in double-layer metal oxide using X-ray photoelectron spectroscopy

2020 ◽  
Vol 739 ◽  
pp. 136973
Author(s):  
Hidetaka Takaki ◽  
Keita Shinzato ◽  
Shuhei Inoue ◽  
Hiroki Miyaoka ◽  
Takayuki Ichikawa ◽  
...  
Keyword(s):  
Metal Oxide ◽  
Double Layer ◽  
Photoelectron Spectroscopy ◽  
X Ray
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