Strain glass versus antisite disorder induced ferromagnetic state in Fe doped Ni–Mn–In Heusler martensites

Fe doping in Ni$_2$Mn$_{1.5}$In$_{0.5}$ results in suppression of the martensitic phase via two contrasting routes. In Ni$_2$Mn$_{1.5 − x}$FexIn$_{0.5}$, the martensitic phase is converted to a strain glassy phase, while in Ni$_{2 − y}$FeyMn$_{1.5}$In$_{0.5}$, a cubic ferromagnetic phase results at the expense of the martensite. Careful studies of magnetic and structural properties reveal the presence of the impurity $γ$-(Fe,Ni) phase as the reason for the emergence of non-ergodic strain glassy phase when Fe is sought to be doped at Y/Z (Mn) sites of X$_2$YZ Heusler alloy. Whereas attempts to dope Fe in the X (Ni) sublattice result in an A2 type antisite disorder that promotes a ferromagnetic ground state

Randomly packed Ni2MnInNi_2MnIn and NiMnNiMn structural units in off-stoichiometric Ni2Mn2−yInyNi_{2}Mn_{2−y} In_{y} alloys

$Ni_2Mn_{2−y}In_y$ alloys transform from the martensitic $L1_0$ antiferromagnetic ground state near $y = 0$ to the austenitic ferromagnetic $L2_1$ Heusler phase near $y = 1$ due to doping of $In$ impurity for $Mn$. The off-stoichiometric alloys prepared by rapid quenching are structurally metastable and dissociate into a mixture of $L2_1$ ($Ni_2MnIn$) and $L1_0$ ($NiMn$) phases upon temper annealing. Despite this structural disintegration, the martensitic transformation temperature remains invariant in the temper annealed alloys. Investigations of thelocal structure of the constituent atoms reveal the presence of strongly coupled $Ni_2MnIn$ and $NiMn$ structural units in the temper annealed as well as the rapidly quenched off-stoichiometric $Ni_2Mn_{2−y}In_y$ alloys irrespective of their crystal structure. This random packing of the $L2_1$ and $L1_0$ structural units seems to be responsible for invariance of martensitic transition temperature in the temper annealed alloys as well as the absence of strain glass transition in rapidly quenched alloys

Understanding the local structures of Eu and Zr in Eu<SUB>2</SUB>O<SUB>3</SUB> doped and coated ZrO<SUB>2</SUB> nanocrystals by EXAFS study

The role of surface coating, doping, and heating on the modification of crystal structure of ZrO<SUB>2</SUB>, on the local structure of Zr and Eu, and on the photoluminescence properties of Eu<SUB>2</SUB>O<SUB>3</SUB> doped and coated ZrO<SUB>2</SUB> nanocrystals has been studied. X-ray absorption fine structure measurements were carried out to understand the local environment surrounding Zr and Eu ions in Eu-doped and coated ZrO<SUB>2</SUB> nanocrystals. It is found that the local structure of Zr ion has been modified by changing the crystal phase and surface coating. The Zr−Zr bond length is 3.447 Å because of eight neighbors for 1100 °C heated undoped ZrO<SUB>2</SUB>, and the Zr−Zr bond lengths are 3.481 and 3.642 Å because of four and eight neighbors for 1100 °C heated Eu-doped ZrO<SUB>2</SUB> sample. The oxygen ions around the central Eu ion are distributed in two shells with bond lengths of 2.26 Å and 2.45 Å in coated sample, whereas there is one shell with bond length of 2.32 Å for doped sample prepared at 1100 °C. Analysis suggests that the interatomic distance between Eu and neighboring atoms, the coordination number, and the bond length of doped nanocrystals are different from the coated nanocrystals. It is observed that local structures play the most important role on the modifications of luminescence properties observed in Eu-doped and coated ZrO<SUB>2</SUB> nanocrystals

Liquid phase selective oxidation of benzene over nanostructured Cu xCe1-xO2-\u3b4 (0.03 64 x 64 0.15)

Liquid phase direct oxidation of benzene to phenol was carried out over copper loaded on oxides such as ceria, alumina, magnesia, ferric oxide, zinc oxide with 30% H2O2 as oxidant under atmospheric pressure. Of all the catalytic formulations prepared via a novel solution combustion synthesis, the ceria based catalysts showed highest activity. Particularly, over the Cu0.10Ce0.90O2_delta catalyst, 43% conversion of benzene with 100% selectivity was observed at 70 degrees C and atmospheric pressure. The activity of this combustion synthesized catalyst is also higher than the corresponding catalyst prepared by incipient wetness impregnation and coprecipitation methods. Powder XRD, TEM and XPS studies show ionically substituted copper over ceria as the predominant phase in the combustion derived catalyst whereas on the impregnated and coprecipitated catalysts copper is present in the dispersed copper oxide form. Influences of temperature and time, H2O2 concentration and solvent have also been investigated. Enhanced activity over the combustion synthesized catalyst wherein Cu2+ ion is present as substitutional ion in ceria has been attributed to Cu-O-Ce ionic interaction. Ionic substitution also brings stability to the active copper ion component in the combustion synthesized catalyst with lower risk of Cu-leaching as compared to the corresponding impregnated and coprecipitated catalysts as evidenced from the recycling experiments. (C) 2014 Elsevier B.V. All rights reserved

Combustion synthesized copper-ion substituted FeAl2O4 (Cu0.1Fe0.9Al2O4): A superior catalyst for methanol steam reforming compared to its impregnated analogue

A series of copper ion substituted MAl2O4 (M = Mg, Mn, Fe and Zn) spinels is prepared by a single step solution combustion synthesis (SCS) and tested for methanol steam reforming (MSR). The copper ion substituted Cu0.1Fe0.9Al2O4 appears to be the most active, showing similar to 98% methanol conversion at 300 degrees C with similar to 5% CO selectivity at GHSV = 30,000 h(-1) and H2O:CH3OH =1.1. The analogous impregnated catalyst, CuO (10 at%)/FeAl2O4, is found to be much less active. These materials are characterized by XRD, H-2-TPR, BET, HRTEM, XPS and XANES analyses. Spinel phase formation is highly facilitated upon Cu-ion substitution and Cu loading beyond 10 at% leads to the formation of CuO as an additional phase. The ionic substitution of copper in FeAl2O4 leads to the highly crystalline SCS catalyst containing Cu2+ ion sites that are shown to be more active than the dispersed CuO nano-crystallites on the FeAl2O4 impregnated catalyst, despite its lower surface area. The as prepared SCS catalyst contains also a portion of copper as Cu1+ that increases when subjected to reforming atmosphere. The MSR activity of the SCS catalyst decreases with time-on-stream due to the sintering of catalyst crystallites as established from XPS and HRTEM analyses

Liquid phase selective oxidation of benzene over nanostructured CuxCe1-xO2-delta (0.03 <= x <= 0.15)

Liquid phase direct oxidation of benzene to phenol was carried out over copper loaded on oxides such as ceria, alumina, magnesia, ferric oxide, zinc oxide with 30% H2O2 as oxidant under atmospheric pressure. Of all the catalytic formulations prepared via a novel solution combustion synthesis, the ceria based catalysts showed highest activity. Particularly, over the Cu0.10Ce0.90O2_delta catalyst, 43% conversion of benzene with 100% selectivity was observed at 70 degrees C and atmospheric pressure. The activity of this combustion synthesized catalyst is also higher than the corresponding catalyst prepared by incipient wetness impregnation and coprecipitation methods. Powder XRD, TEM and XPS studies show ionically substituted copper over ceria as the predominant phase in the combustion derived catalyst whereas on the impregnated and coprecipitated catalysts copper is present in the dispersed copper oxide form. Influences of temperature and time, H2O2 concentration and solvent have also been investigated. Enhanced activity over the combustion synthesized catalyst wherein Cu2+ ion is present as substitutional ion in ceria has been attributed to Cu-O-Ce ionic interaction. Ionic substitution also brings stability to the active copper ion component in the combustion synthesized catalyst with lower risk of Cu-leaching as compared to the corresponding impregnated and coprecipitated catalysts as evidenced from the recycling experiments. (C) 2014 Elsevier B.V. All rights reserved

Combustion synthesized copper-ion substituted FeAl2O4 (Cu0.1Fe0.9Al2O4): A superior catalyst for methanol steam reforming compared to its impregnated analogue

A series of copper ion substituted MAl2O4 (M = Mg, Mn, Fe and Zn) spinels is prepared by a single step solution combustion synthesis (SCS) and tested for methanol steam reforming (MSR). The copper ion substituted Cu0.1Fe0.9Al2O4 appears to be the most active, showing ~98% methanol conversion at 300 °C with ~5% CO selectivity at GHSV = 30,000 h-1 and H2O:CH3OH = 1.1. The analogous impregnated catalyst, CuO (10 at%)/FeAl2O4, is found to be much less active. These materials are characterized by XRD, H2-TPR, BET, HRTEM, XPS and XANES analyses. Spinel phase formation is highly facilitated upon Cu-ion substitution and Cu loading beyond 10 at% leads to the formation of CuO as an additional phase. The ionic substitution of copper in FeAl2O4 leads to the highly crystalline SCS catalyst containing Cu2+ ion sites that are shown to be more active than the dispersed CuO nano-crystallites on the FeAl2O4 impregnated catalyst, despite its lower surface area. The as prepared SCS catalyst contains also a portion of copper as Cu1+ that increases when subjected to reforming atmosphere. The MSR activity of the SCS catalyst decreases with time-on-stream due to the sintering of catalyst crystallites as established from XPS and HRTEM analyses.Peer Reviewe

Understanding the anomalous behavior of Vegard's law in Ce1-xMxO2 (M = Sn and Ti; 0 < x <= 0.5) solid solutions

The dependence of the lattice parameter on dopant concentration in Ce1-xMxO2 (M = Sn and Ti) solid solutions is not linear. A change towards a steeper slope is observed around x similar to 0.35, though the fluorite structure (space group Fm3m) is preserved up to x = 0.5. This phenomenon has not been observed for Ce1-xZrxO2 solid solutions showing a perfectly linear decrease of the lattice parameter up to x = 0.5. In order to understand this behavior, the oxidation state of the metal ions, the disorder in the oxygen substructure and the nature of metal-oxygen bonds have been analyzed by XPS, Sn-119 Mossbauer spectroscopy and X-ray absorption spectroscopy. It is observed that the first Sn-O coordination shell in Ce1-xSnxO2 is more compact and less flexible than that of Ce-O. The Sn coordination remains symmetric with eight equivalent, shorter Sn-O bonds, while Ce-O coordination gradually splits into a range of eight non-equivalent bonds compensating for the difference in the ionic radii of Ce4+ and Sn4+. Thus, a long-range effect of Sn doping is hardly extended throughout the lattice in Ce1-xSnxO2. In contrast, for Ce1-xZrxO2 solid solutions, both Ce and Zr have similar local coordination creating similar rearrangement of the oxygen substructure and showing a linear lattice parameter decrease up to 50% Zr substitution. We suggest that the localized effect of Sn substitution due to its higher electronegativity may be responsible for the deviation from Vegard's law in Ce1-xSnxO2 solid solutions

Methanol steam reforming behavior of sol-gel synthesized nanodimensional CuxFe1-xAl2O4 hercynites

This work reports the outstanding catalytic activity behavior of sol-gel synthesized nanostructured CuxFe1-xAl2O4 (0.3¿=¿x¿=¿0.8; named as CuFeAln, where n¿=¿30, 40, 50, 60, 70 and 80) hercynites towards methanol steam reforming (MSR) for hydrogen generation. Based on the durability studies, we had categorized the higher Cu-doped hercynites (CuFeAl70 and CuFeAl80) as the more effective in regard to activity and stability (maintenance of a methanol conversion of ~80% with low CO selectivity of 2% after 50¿h of continuous operation at 275¿°C for CuFeAl80) when compared with the lower Cu-doped counterparts (CuFeAl30 and CuFeAl40). The specific surface area of all the materials was about 50 m2¿g-1 and they had similar reduction characteristics as obtained from H2-TPR analysis. The lower reducibility below 280¿°C of CuFeAl70 and CuFeAl80 was correlated with the higher stability of these samples during time on stream operation. The powder XRD analyses had shown pure phase hercynite formation with the gradual increase of Cu-doping, while there occurred a phase segregation in the reforming atmosphere leading to the formation of metallic copper. High resolution microstructural analyses had confirmed single phase hercynite formation at nanoscale and a reduction of copper subsequent to ageing as well as certain growth of the copper metal particles (from ~5¿nm to ~8¿nm) corroborating the XRD studies. The surface features from in-situ XPS had also suggested formation of reduced copper species, which was much lower for the higher Cu-doped samples. Cu K edge XANES spectral analyses also pointed to lower occurrence of reduced copper in the aged samples of higher Cu-doped hercynites. The experimental findings had been explained on the basis of partial breakdown of the spinel lattice structure leading to the formation of CuO, followed by its reduction to metallic copper nanocrystallites in the MSR atmosphere. A definite ratio of the reduced to oxidized copper species was maintained with time on stream and this caused nearly stable conversion behavior of the catalysts in methanol steam reforming.Peer Reviewe