12 research outputs found
Black Titania and Niobia within Ten Minutes - Mechanochemical Reduction of Metal Oxides with Alkali Metal Hydrides.
Partially or fully reduced transition metal oxides show extraordinary electronic and catalytic properties but are usually prepared by high temperature reduction reactions. This study reports the systematic investigation of the fast mechanochemical reduction of rutile-type TiO2 and H-Nb2 O5 to their partially reduced black counterparts applying NaH and LiH as reducing agents. Milling time and oxide to reducing agent ratio show a large influence on the final amount of reduced metal ions in the materials. For both oxides LiH shows a higher reducing potential than NaH. An intercalation of Li+ into the structure of the oxides was proven by PXRD and subsequent Rietveld refinements as well as 6 Li solid-state NMR spectroscopy. The products showed a decreased band gap and the presence of unpaired electrons as observed by EPR spectroscopy, proving the successful reduction of Ti4+ and Nb5+ . Furthermore, the developed material exhibits a significantly enhanced photocatalytic performance towards the degradation of methylene blue compared to the pristine oxides. The presented method is a general, time efficient and simple method to obtain reduced transition metal oxides
Black Titania and Niobia within Ten Minutes : Mechanochemical Reduction of Metal Oxides with Alkali Metal Hydrides
Partially or fully reduced transition metal oxides
show extraordinary electronic and catalytic properties but are
usually prepared by high temperature reduction reactions.
This study reports the systematic investigation of the fast
mechanochemical reduction of rutile-type TiO2 and H-Nb2O5
to their partially reduced black counterparts applying NaH
and LiH as reducing agents. Milling time and oxide to
reducing agent ratio show a large influence on the final
amount of reduced metal ions in the materials. For both
oxides LiH shows a higher reducing potential than NaH. An
intercalation of Li+ into the structure of the oxides was
proven by PXRD and subsequent Rietveld refinements as well
as 6
Li solid-state NMR spectroscopy. The products showed a
decreased band gap and the presence of unpaired electrons
as observed by EPR spectroscopy, proving the successful
reduction of Ti4+ and Nb5+. Furthermore, the developed
material exhibits a significantly enhanced photocatalytic
performance towards the degradation of methylene blue
compared to the pristine oxides. The presented method is a
general, time efficient and simple method to obtain reduced
transition metal oxides
Highly Exothermic and Fast Mechanochemical Redox and Intercalation Reactions of V<sub>2</sub>O<sub>5</sub> with Sodium Hydride
Vanadium oxides exhibit promising characteristics for
electrochemical
energy storage, owing to their capability to switch between different
oxidation states, in combination with the incorporation of alkali
metals. Here, we report on a systematic investigation of the mechanochemical
reduction of V2O5 with NaH. In contrast to conventional
high-temperature synthesis methods, the mechanochemical reaction occurs
already after a few minutes. We observed a mixture of different (sodium)
vanadium oxides with vanadium oxidation states ranging from +III to
+V. Remarkably, these highly exothermic self-propagating reactions
occur even within a rudimentary pistil-mortar setup. Hereby, the hydride
concentration has a greater effect on the final sample composition
than the milling time. In general, higher percentages of sodium vanadates
are formed instead of vanadium oxides, and the lower oxidation states
of vanadium are accessible with increasing amounts of NaH. Theoretical
calculations confirm these experimental observations and emphasize
the central role of sodium vanadates, especially with vanadium in
the +V oxidation state, in carrying out the observed exothermic reactions.
This comprehensive study sheds light on the mechanochemical reduction
of vanadium oxides and underlines their potential for further development
of electrochemical energy storage systems
Highly Exothermic and Fast Mechanochemical Redox and Intercalation Reactions of V<sub>2</sub>O<sub>5</sub> with Sodium Hydride
Vanadium oxides exhibit promising characteristics for
electrochemical
energy storage, owing to their capability to switch between different
oxidation states, in combination with the incorporation of alkali
metals. Here, we report on a systematic investigation of the mechanochemical
reduction of V2O5 with NaH. In contrast to conventional
high-temperature synthesis methods, the mechanochemical reaction occurs
already after a few minutes. We observed a mixture of different (sodium)
vanadium oxides with vanadium oxidation states ranging from +III to
+V. Remarkably, these highly exothermic self-propagating reactions
occur even within a rudimentary pistil-mortar setup. Hereby, the hydride
concentration has a greater effect on the final sample composition
than the milling time. In general, higher percentages of sodium vanadates
are formed instead of vanadium oxides, and the lower oxidation states
of vanadium are accessible with increasing amounts of NaH. Theoretical
calculations confirm these experimental observations and emphasize
the central role of sodium vanadates, especially with vanadium in
the +V oxidation state, in carrying out the observed exothermic reactions.
This comprehensive study sheds light on the mechanochemical reduction
of vanadium oxides and underlines their potential for further development
of electrochemical energy storage systems
Suppressed Negative Information and Future Underperformance
I present evidence of inefficient information processing in equity markets by documenting that negative information withheld by securities analysts is incorporated in stock prices with a significant delay. I estimate the extent of the withheld negative information based on the proportion of analysts who stop revising their annual earnings forecasts. This measure predicts negative earnings surprises and negative price reaction around earnings announcements. It could also be used to generate profitable trading strategies. I show that institutions tend to sell their stock holdings as my measure of unreported negative news increases, thus ameliorating the mispricing. Copyright 2008, Oxford University Press.