University of Münster

About: University of Münster is a education organization based out in Münster, Germany. It is known for research contribution in the topics: Population & Catalysis. The organization has 35609 authors who have published 69059 publications receiving 2278534 citations. The organization is also known as: University of Munster & University of Muenster.

Melting and freezing of water in cylindrical silica nanopores

Abstract: Freezing and melting of H2O and D2O in the cylindrical pores of well-characterized MCM-41 silica materials (pore diameters from 2.5 to 4.4 nm) was studied by differential scanning calorimetry (DSC) and 1H NMR cryoporometry. Well-resolved DSC melting and freezing peaks were obtained for pore diameters down to 3.0 nm, but not in 2.5 nm pores. The pore size dependence of the melting point depression ΔTm can be represented by the Gibbs–Thomson equation when the existence of a layer of nonfreezing water at the pore walls is taken into account. The DSC measurements also show that the hysteresis connected with the phase transition, and the melting enthalpy of water in the pores, both vanish near a pore diameter D* ≈ 2.8 nm. It is concluded that D* represents a lower limit for first-order melting/freezing in the pores. The NMR spin echo measurements show that a transition from low to high mobility of water molecules takes place in all MCM-41 materials, including the one with 2.5 nm pores, but the transition revealed by NMR occurs at a higher temperature than indicated by the DSC melting peaks. The disagreement between the NMR and DSC transition temperatures becomes more pronounced as the pore size decreases. This is attributed to the fact that with decreasing pore size an increasing fraction of the water molecules is situated in the first and second molecular layers next to the pore wall, and these molecules have slower dynamics than the molecules in the core of the pore.

Suppression Pattern of Neutral Pions at High Transverse Momentum in Au plus Au Collisions at root S-NN=200 GeV and Constraints on Medium Transport Coefficients

Abstract: For Au + Au collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, p(T), up to 20 GeV/c. A fivefold suppression is found, which is essentially constant for 5 in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au + Au collisions.

Unfolding the Mechanism of Sodium Insertion in Anatase TiO2 Nanoparticles

Abstract: It is frequently assumed that sodium-ion battery chemistry exhibits a behavior that is similar to the more frequently investigated lithium-ion chemistry. However, in this work it is shown that there are great, and rather surprising, differences, at least in the case of anatase TiO2. While the generally more reducing lithium ion is reversibly inserted in the anatase TiO2 lattice, sodium ions appear to partially reduce the rather stable oxide and form metallic titanium, sodium oxide, and amorphous sodium titanate, as revealed by means of in situ X-ray diffraction, ex situ X-ray photoelectron spectroscopy, scanning electron microscopy, and Raman spectroscopy. Nevertheless, once the electrochemical transformation of anatase TiO2 is completed, the newly formed material presents a very stable long-term cycling performance, excellent high rate capability, and superior coulombic efficiency, highlighting it as a very promising anode material for sodium-ion battery applications.

Tris(pentafluorophenyl)borane: a special boron Lewis acid for special reactions

Abstract: Tris(pentafluorophenyl)borane is best known for its role as an excellent activator component in homogeneous Ziegler–Natta chemistry. However, the special properties of B(C6F5)3 have made this strong boron Lewis acid an increasingly used catalyst or stoichiometric reagent in organic and organometallic chemistry. This includes catalytic hydrometallation reactions, alkylations and catalyzed aldol-type reactions. B(C6F5)3 catalyzes tautomerizations and can sometimes stabilize less favoured tautomeric forms by adduct formation. It induces some rather unusual reactions of early metal acetylide complexes and can help in stabilizing uncommon coordination geometries of carbon. The growing number of such examples indicates an increasing application potential of the useful Lewis acid B(C6F5)3 aside from its established role in olefin polymerization catalysis.