The Use of Sustainable Transition Metals for the Cycloaddition of Epoxides and CO2 under Mild Reaction Conditions

Following green chemistry principles, we present a one pot synthesis of zinc curcumin complex as a homogeneous, sustainable catalyst for cyclic carbonate (CC) synthesis from CO₂ and a variety of terminal and internal epoxides under 1 bar CO₂ at 60 °C using DMSO as a solvent. Zinc curcumin ( Zn-Cur ) complex was identified via ¹H/¹³C NMR and ATR-FTIR spectroscopies, elemental analysis, ionic conductivity, and quantitative silver nitrate test to confirm a 1 : 1 molar ratio of metal to the ligand. Interestingly, Zn-Cur showed an outstanding performance in catalysing the synthesis of renewable CCs including dimeric pinene and limonene carbonates. In this context, other metal complexes, including magnesium (Mg^II), calcium (Ca^II), and nickel (Ni^II) complexes showed good to excellent catalytic activity. Furthermore, a plausible reaction mechanism was investigated by density functional theory (DFT) calculations. The reaction was found to be overall exergonic by 39 kJ/mol and the rate determining step was CO₂ insertion, which is in good agreement with the experimental findings.     

Catalytic performance of Ni-Al layered double hydroxides in CO purification processes

Ni-Al layered double hydroxides with Ni²⁺/Al³⁺ molar ratios of 1.5 and 3.0 have been synthesized by co-precipitation and studied as catalyst precursors for purification of CO-containing gas-mixtures by means of CO oxidation to CO₂ and conversion of CO by water vapor (water-gas shift reaction). The influence of the alkali additives (K⁺ ions) on the water-gas shift activity has been also examined. It was established that the catalytic activity of both reactions increases with the temperature and the nickel content. Hypothetic schemes are proposed about activation of the catalysts in the WGSR and CO oxidation including redox Ni²⁺ ? Ni³⁺ transition on the catalyst surface. The activity in WGSR is positively affected by the presence of potassium promoter, depending on its amount. The sample with higher nickel loading is the most effective catalyst as for CO oxidation as well as for WGSR at intermediate temperatures after potassium promotion.     

A sulfide/polysulfide-based ionic liquid electrolyte for quantum dot-sensitized solar cells

Further development of quantum dot-sensitized solar cells (QDSCs) will require long-term stability in addition to the continuous increase of photovoltaic (PV) conversion efficiency achieved in the last years. We report a robust S(2-)/S(n)(2-) electrolyte that has been specifically designed for compatibility with CdSe quantum dots in sensitized solar cells. The new pyrrolidinium ionic liquid reaches 1.86% efficiency and a short-circuit current close to 14 mA·cm(-2) under air-mass 1.5 global illumination and improves the device lifetime with good photoanode stability over 240 h. PV characterization showed that the solar cell limitations relate to poor catalysis of regeneration at the counter electrode and high recombination. Further improvement of these factors in the robust electrolyte configuration may thus have a significant impact for advancing the state-of-the-art in QDSCs.     

Effect of copper oxide on the catalytic activity of iron-chromia catalyst for water gas shift reaction

It has been established that copper oxide promotes the catalytic activity of iron-chromia catalyst in the water gas shift reaction due to the formation of catalytically active aggregates. However, due to their gradual recrystallization and sintering into larger copper particles, the promoting effect sharply decreases.

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THz coherent emission from quantized metallic films under ultrafast IR excitation

2 laser is studied theoretically. The consideration is based on the second-order perturbation for the density matrix under the collisionless regime. The numerical results for the response in the THz spectral region as a function of the pump frequency and the pulse duration demonstrate the possibility of efficient excitation of the THz emission from the quantized metallic films. Received: 20 September 1998 / Revised version: 27 January 1999     

Resonant generation of a difference harmonic at a quantized metallic film

Received: 20 September 1998 / Revised version: 27 January 1999     

Carbon Monoxide Activation by a Molecular Aluminium Imide: C−O Bond Cleavage and C−C Bond Formation

Anionic molecular imide complexes of aluminium are accessible via a rational synthetic approach involving the reactions of organo azides with a potassium aluminyl reagent. In the case of K₂[( NON )Al(NDipp)]₂ ( NON =4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene; Dipp=2,6-diisopropylphenyl) structural characterization by X-ray crystallography reveals a short Al−N distance, which is thought primarily to be due to the low coordinate nature of the nitrogen centre. The Al−N unit is highly polar, and capable of the activation of relatively inert chemical bonds, such as those found in dihydrogen and carbon monoxide. In the case of CO, uptake of two molecules of the substrate leads to C−C coupling and C≡O bond cleavage. Thermodynamically, this is driven, at least in part, by Al−O bond formation. Mechanistically, a combination of quantum chemical and experimental observations suggests that the reaction proceeds via exchange of the NR and O substituents through intermediates featuring an aluminium-bound isocyanate fragment.     

Insights into scanning probe high-field chemistry of diphenylgermane

Experiments and simulations are used to elucidate a new class of chemical reactions occurring near the tip-sample interface during high field chemistry of diphenylgermane. Current data during writing and bias dependent growth rate are analyzed, supplemented with data from ionization mass spectrometry, and compared with the simulation results.     

Quantum wells under an in-plane magnetic field: Effect of the composition parameters on excited electron energy splitting

The dependence of the electronic spin-splitting energy on the composition parameters (x,y) in In_xGa_1?xAs–In_yAl_1?yAs-based quantum wells, has been calculated. InGaAs narrow gap structures, subjected to in-plane magnetic fields, have been selected because these structures have a big Landè factor. The dependence of the Landé factor both on the applied fields and composition parameters has been included for fixed well width and external electric field. Contributions from the interfaces and strain, which also depend on the composition, are included. Spin-splitting energy and density of states show a strong dependence on the above parameters.