2 research outputs found
Heusler Alloys: A Group of Novel Catalysts
In
this study, we investigated the catalytic properties of various
Heusler alloys for the hydrogenation of propyne and the oxidation
of carbon monoxide. For propyne hydrogenation, Co<sub>2</sub>FeGe
alloy showed a higher activity than that of elemental Co, where neither
Fe nor Ge showed any activity. This clearly indicates an alloying
effect. For the oxidation of carbon monoxide, although most alloys
showed a significant change in catalytic activity during measurement
due to an irreversible oxidation of the alloy, Co<sub>2</sub>TiSn
alloy showed a very small change. The results indicate that the catalytic
activity and stability of a Heusler alloy can be tuned by employing
an appropriate set of elements
Fast Oxidation of Porous Cu Induced by Nano-Twinning
The
fcc lattice of porous Cu prepared by dealloying Al<sub>2</sub>Cu with
HCl aqueous solution exhibits a high density of twinning defects with
an average domain size of about 3 nm along the ⟨111⟩
directions. The high density of twinning was verified by X-ray diffraction
and qualitatively interpreted by a structural model showing the 5%
probability of twinning defect formation. Most of the twinning defects
disappeared after annealing at 873 K for 24 h. Twinned Cu reveals
much faster oxidation rate in comparison to that without (or with
much fewer) twinning defects, as shown by X-ray diffraction and hydrogen
differential scanning calorimetry. Using ab initio DFT calculations,
we demonstrate that twinning defects in porous Cu are able to form
nucleation centers for the growth of Cu<sub>2</sub>O. The geometry
of the V-shaped edges on the twinned {211} surfaces is favorable for
formation of the basic structural elements of Cu<sub>2</sub>O. The
fast oxidation of porous Cu prepared by dealloying can thus be explained
by the fast formation of the Cu<sub>2</sub>O nucleation centers and
their high density