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This study investigated the homogeneous formation and reduction of NO from the oxidation of CH4/NH3 to understand the effect of the high concentrations of H2O on NO emissions. The experimental results about the effects of excess oxygen ratio, gas compositions including H2O, CO2, NH3 and recycled NO, on NO formation and reduction were presented. The mechanism about the effects of high concentration of H2O and combined effect of H2O/CO2 on NO formation and reduction has been discussed. The results indicates that NO formation was markedly enhanced at high concentrations of H2O, which were mainly attributed to the increased OH radicals with steam addition at oxygen-rich conditions. By contrast, the radicals were consumed by reduction radicals, such as CO, H, and CHi radicals, under oxygen-lean conditions. NO concentrations followed the sequence of H2O/Ar > H2O/CO2 > CO2/Ar under both the oxygen-rich and oxygen-lean conditions, which meant that the highest and lowest NO emissions were recorded in Ar/H2O and CO2/Ar respectively. The combined H2O/CO2 concentration accordingly exerted an effective impact on NO reduction. The results about the effect of NH3 concentration in fuel on NO emission showed that NO emission increased with increasing NH3 concentration. Furthermore, NO reburning results implied that with increasing NO concentration, the total NO reduction increased, whereas the reduction ratio decreased.

By combining experimental observations on Gd doped fuel with a theoretical understanding, the variation in thermal conductivity with Gd concentration and accommodation mechanism has been modelled. Four types of Gd accommodation mechanisms have been studied. In UO2−x, isolated substitutional Gd3+ ions are compensated by oxygen vacancies and { 2 Gd U ’ : V O ⋅ ⋅ } × defect clusters. In UO2, isolated substitutional Gd3+ ions are compensated by U5+ ions and { Gd U ’ : U U ⋅ } × defect clusters. The results indicate that defect clusters can be considered as less effective phonon scatterers and therefore result in less thermal conductivity degradation. The thermal conductivity predicted for UO2 with { G d U ′ : U U ⋅ } × defect clusters is in good agreement with experimental data for UO2 with 5 wt% Gd2O3. This supports the previous theoretical results that Gd is accommodated through defect clusters { Gd U ’ : U U ⋅ } × in UO2 in the presence of excess oxygen.

The low-temperature NO decomposition with high efficiency remains a grand challenge. Herein, we report an attractive approach for the low-temperature NO decomposition by microwave catalysis over BaMnO 3 and substituted Ba 0.8 A 0.2 MnO 3 (A Ca, K, La) catalysts. Importantly, impressively high NO conversion and N 2 selectivity with 99.9% and 99.9%, respectively, were achieved over Ba 0.8 K 0.2 MnO 3 catalyst at 250 °C. Comparatively, under identical conditions in the conventional reaction mode, the highest NO conversion and N 2 yield are respectively only 45.4% and 28.7% for Ba 0.8 K 0.2 MnO 3 at 650 °C. Unexpectedly, the effect of Ca, K and La substitution is different in these two reaction modes. The catalysts were characterized by H 2 -TPR, O 2 -TPD, and microwave absorbing properties to illustrate possible reasons causing such obvious differences in catalytic performance. The apparent activation energies for BaMnO 3 , Ba 0.8 Ca 0.2 MnO 3 , Ba 0.8 K 0.2 MnO 3 and Ba 0.8 La 0.2 MnO 3 catalysts under microwave irradiation drop down to as low as 33.4, 41.6, 14.7 and 18.2 kJ/mol, separately, suggesting a significant microwave catalytic effect.

This paper investigates the authenticity of the biofuels as an alternative to Jet A fuel. Owing to the fact of reduced CO2 emission quality, biofuels can be used in the field of aviation to substantially reduce the CO2 emission and improve the performance. In this analysis, microalgae Spirulina biofuel was added with Jet-A fuel at different proportions such as 20%, 40%, 60%, 80% and 100%. The proportions used are B20% (20% biofuel with 80% jet-A fuel), B40% (40% biofuel with 60% Jet-A fuel), B60% (60% biofuel with 40% Jet-A fuel), B80% (80% biofuel with 20% Jet-A fuel) and B100% biofuel. All the test results were compared with the neat jet A fuel. The experiments were conducted at different engine speeds. A small experimental jet engine was used to conduct all the experimental tests. Engine performance characteristics and emission characteristics were found for different fuel blends. It is concluded that the biofuel at a lower proportion level with the Jet–A fuel comparatively produced a good result. In terms of thrust and engine speed, the lower level of addition of biofuel is fruitful. The emission level of CO, CO2, and NOx was reduced owing to the presence of excess oxygen content in the blends. However, when the addition percentage was increased, the results produced by them were not positive because of its low energy.

We have studied transport properties of several NdBa 2 Cu 3 O 7-δ superconductors using wide range of excess oxygen content δ. The buckling angle is found to be very sensitive with δ. Disordered copper oxide planes are origins of the superconducting properties controlling of which is possible by changing the buckling angle in superconducting planes in addition to the carrier concentration. A phase diagram consisting of the characteristic temperature T* related to the formation of pseudogap and critical temperature with δ has been obtained. The effect of the changed buckling angle on the pseudogap formation with δ has been also studied.

The effect of Al doping concentration on resistive switching characteristics of Pt/Al-doped HfO x /Cu structures was investigated. According to the X-ray photoelectron spectroscopy (XPS) analysis and the first-principle calculation, the Al doping introduced more oxygen vacancies in HfO x film and these oxygen vacancies can be easily generated along Al dopants. Significant enhancement in resistive switching behaviors was achieved for 6.8% Al-doped HfO x film in terms of ON/OFF ratio, switching voltages and uniformity, whereas the higher Al doping concentration of 9.4% caused excess oxygen vacancies in the film, resulting in the degeneration of switching performance. A schematic diagram based on the formation and rupture of oxygen vacancy filaments was proposed to illustrate the distinct switching behaviors of HfO x and Al-doped HfO x samples. The results indicated that the concentration and distribution of oxygen vacancies played an important role on resistive switching behavior. The reliability properties for the prepared HfO x samples were also investigated. This work might provide a guidance for the further optimization of HfO x -based memory.

Oxy-fuel circulating fluidized bed (CFB) combustion combining the advantages of oxy-fuel combustion and CFB technology is one of the most promising technologies for capturing CO2. However, the emission of N2O in oxy-fuel CFB combustion can be high enough to raise some related environmental issues. This study investigated N2O emission in O2/CO2 CFB combustion with a high oxygen concentration based on the experimental results using a the 0.1 MWth oxy-fuel CFB. This study focused on the operating parameters. It was found that increasing the combustion temperature and overall oxygen concentration can lead to lower N2O emission, while increasing the excess oxygen ratio can lead to higher N2O emission levels. Both gas staging and oxygen staging have slight adverse influences on controlling N2O owing to the higher oxygen concentration in the secondary gas. Finally, the excess oxygen ratio in the primary zone was determined in order to assess the actual effects of gas and oxygen staging on both N2O and NO emissions.

The impact of H 2 as additional reducing agent on the SCR of NO with C 3 H 6 in excess oxygen, was comparatively explored over low noble metal loading (0.5 wt%), Pt/γ-Al 2 O 3 , Pd/γ-Al 2 O 3 , Ir/γ-Al 2 O 3 catalysts. To gain insight into the role of H 2 , the reactions NO + C 3 H 6 + O 2 (R#1), NO + C 3 H 6 + O 2 + H 2 (R#2), NO + H 2 + O 2 (R#3) were employed. In respect to propene oxidation, the Pd > Pt > Ir sequence was obtained under R#1, since they exhibit complete conversion at 220, 250, 325 °C, respectively; all metals exhibit moderate deNO x performances ( X NO, 2 co-presence (R#2) promotes both the NO and C 3 H 6 conversions, which is valid in the whole temperature interval investigated (50–400 °C), being more substantial for Pt/γ-Al 2 O 3 and Ir/γ-Al 2 O 3 , less beneficial for Pd/γ-Al 2 O 3 . A two-maxima feature is obtained on X NO pattern (at ∼100 and ∼230 °C) of Pt and Pd during R#2. The low temperature maximum −attributed to NO reduction by H 2 - is substantially more pronounced on Pt than Pd, offering X NO ∼90% and S N2 ∼85%; the high temperature maximum—attributed to NO reduction by C 3 H 6 —is higher by ∼15% on both Pt and Pd, in respect to the values obtained during R#1, while S N2 remained unaffected. Different X NO pattern with one maximum is obtained over Ir, implying a synergistic interaction between H 2 and C 3 H 6 . This synergy is accompanied by a substantial widening of the NO reduction window toward lower temperatures and a considerable increase on both X NO,max and S N2 (from X NO ∼30% with S N2 ∼55% during R#1 to X NO ∼70% with S N2 ∼95% during R#2). The specific features of all reactions and metals employed are comparatively discussed.

Type III silica samples were implanted with O using a multi-energy process that produced a layer of constant concentration to within ±5% beginning ∼80 nm from the surface and extending to ∼640 nm below the surfaces of the samples. The concentrations of excess oxygen in the layer ranged from 0.035 to ∼2.1at.%. In these samples we show that E′ centers and NBOHCs, as well as the normal cadre of ODC (II) centers, were suppressed, and the optical absorption from 4.7 to 6.4 eV was primarily due to oxygen excess defects. Using Gaussian fitting techniques to examine the optical difference spectra, we have been able to identify four defect centers that are related to excess oxygen defect bands at 4.76 eV, 5.42 eV, 5.75 eV and 6.25 eV.

The cathodes of MFCs are the main bottleneck for practical application; undesired cathode biofilms often cause their breakdown. The goal of this study was to extend cathode life time. Membranes were applied on the air side of the cathodes to limit oxygen penetration and reduce biofilm formation. Two single chamber MFC designs with an electrode spacing of 120 mm (HRT ∼1 week) and 15 mm (HRT 24 h) were investigated in batch operation using a synthetic blackwater at room temperature (23 ±3 °C). At high electrode spacing cathode life time was increased to 217%, with a significantly increase in power densities over time. The Power densities at 15 mm electrode spacing reached 1155 ± 41 mW m−2 with the membrane applied; compared to 460 ± 32 m Wm−2 without membrane. TOC degradation relative to the anode surface at close electrode spacing was near equal at 6.8 ± 2.3 and 7.2 ± 3.0 gm−2 d−1; however, the Coulomb Efficiency with a membrane increased from 28 ± 10% to 54 ± 13%. CV analysis after operation showed considerably higher ORR activity of the cathodes covered by a membrane.

As one of the most promising carbon capture technologies for coal-fired power plants, oxy-coal combustion has attracted wide interests during the last two decades. In comparison to atmospheric oxy-fuel combustion, pressurized oxy-fuel combustion has the potential to further reduce the energy penalties caused by the carbon capture and storage and improve the net power plant efficiency. Although many researchers have investigated the NOx emissions of atmospheric oxy-coal combustion, the NOx emission behaviors under pressurized oxy-coal combustion conditions are much less understood and further comprehensive experimental investigations with continuous fuel-feeding pressurized oxy-coal combustion systems are needed in order to fill this knowledge gap. In the present study, a series of oxy-coal combustion experiments were conducted in a 30 kWth pressurized fluidized bed combustor. The effects of combustion pressure, bed temperature and excess oxygen on the NOx emissions were investigated systematically. The experimental results have shown that an increase in combustion pressure from 0.1 MPa to 0.4 MPa leads to a significant reduction in NOx emissions. An increase in bed temperature or excess oxygen results in higher NOx emissions under the higher combustion pressure conditions, which is consistent with what is observed under the atmospheric pressure combustion condition. Besides, it is found that the promoting effect of temperature increase on NOx emissions under the higher combustion pressures is weaker than that under the atmospheric pressure.

A series of hexagonal RMnO{sub 3} (R=Y, Ho–Lu) compounds are first annealed in various highly oxidizing conditions to show that for the largest R constituents, Y and Ho, it is possible to load the phases with large amounts of excess oxygen. Within the oxygen-annealed samples we identify new heavily-oxygenated phases, that is, YMnO{sub 3.35} and HoMnO{sub 3.34}. The former is then thoroughly characterized by thermogravimetric analysis, X-ray diffraction and electron diffraction. These studies evidence a hexagonal sub-cell (a{sub S}≈3.578 A (a{sub H}/√(3)), c{sub S}≈11.18 A, space group P6{sub 3}mc) and satellites, associated with two modulation vectors q{sup →}{sub 1}{sup ⁎}≈0.41a{sup →}{sub S}{sup ⁎}+0.41b{sup →}{sub S}{sup ⁎}+1/3c{sup →}{sub S}{sup ⁎}andq{sup →}{sub 2}{sup ⁎}=(1/2). The results are interpreted by the formation of a modulated composite structure, resulting from the evolution of the hexagonal parent YMnO{sub 3+δ} structure toward a reduced pyrochlore-type structure Y{sub 2}Mn{sub 2}O{sub 7−x}, in long- and short-range ordering. - Graphical abstract: Hexagonal RMnO{sub 3+δ} phases are commonly taken as oxygen-stoichiometric. Here we show that the R=Y and Ho phases can be loaded with excess oxygen up to δ≈0.35 through high-pressure oxygenation annealing. Formation of a new composite structure composed of hexagonal-like RMnO{sub 3+δ} and pyrochlore-like RMnO{sub 3.5−δ} constituents ismore » demonstrated in the case of R=Y. - Highlights: • Hexagonal RMnO{sub 3+δ} phases are commonly taken as oxygen-stoichiometric. • For R=Y and Ho phases excess-oxygen loading is possible. • Single-phase samples with a new composite structure are obtained at δ≈0.35. • The new structure is composed of hexagonal- and pyrochlore-like units.« less

We have succeeded in synthesizing hole-doped bulk superconductors of La 1.8-x Eu 0.2 Ca x CuO 4 ( x = 0.05 and 0.10) with the Nd 2 CuO 4 -type structure by means of the structural transformation at low temperatures from the K2NiF4-type structure via the Nd 4 Cu 2 O 7 -type structure. Superconductivity has appeared through the removal of excess oxygen by the reduction annealing in vacuum. Values of the superconducting transition temperature, T c , are 13 and 6 K for x = 0.05 and 0.10, respectively. These values are smaller than those of T’-La 1.8-x Eu 0.2 Sr x CuO 4 .

Delafossite-type CuLnO2 (Ln = La, Y) was synthesized and investigated their oxygen storage capacity (OSC) under oxidation/reduction cycle. CuLaO2 was synthesized by heating at 1000 °C for 6 h in N2 flow and CuYO2 was synthesized by heating of Cu2Y2O5 at 1190 °C for 1 h in N2 flow. The oxygen storage capacity values of CuLaO2 and CuYO2 at lower temperature were larger than that of CeO2-based materials which is used as a promoter of an automobile catalyst. The stability of delafossite-type CuLnO2 under cyclic oxidation/reduction atomosphere was investigated using XRD analysis. During the OSC measurement up to 700 °C, CuLaO2 decomposed to La2CuO4 and Cu2O. CuYO2 also partially decomposed to Y2O3, Cu2Y2O5 and Cu2O. These results suggest that oxidative decomposition of CuLnO2 occurred at high temperature. In lower temperature range, delafossite-type CuLaO2+x containing excess oxygen existed in both oxidative and reductive atmosphere and it partially decomposed during a hundred of oxidation/reduction cycles.

We have synthesized La 2− x Sm x CuO 4 (0 ⩽ x ⩽ 2.0) with the Nd 2 CuO 4 structure via a molten alkaline hydroxide route at temperatures as low as 400–480 °C. After reduction heat treatment in vacuum at 600–750 °C for removal of excess oxygen atoms at the interstitial apical site, superconductivity with T c = 20–24 K was observed in the samples with x = 0.05–1.0. The superconducting volume fraction is nearly 100% for x = 0.3–0.7. Our results demonstrate that La 2− x Sm x CuO 4 with no nominal carrier doping is a bulk superconductor.

Δημοσίευση σε επιστημονικό περιοδικό Summarization: In the present work, two different methods of catalyst promotion, the electrochemical promotion (EP) and the conventional promotion (CP), were comparatively applied on a catalytic system of significant environmental and practical importance: the N2O reduction by hydrocarbons (alkanes and alkenes), in the presence or absence of O2, over Pd catalysts. A galvanic cell of the type Pd/K+-conducting β″-Al2O3/Au was constructed for the application of the EP concept whereas the CP concept was investigated via a series of highly dispersed Pd/γ-Al2O3 catalysts, conventionally promoted (by impregnation) with K modifier. Given that EP is a straightforward, efficient and in situ way for investigating the effect of a promoter on a catalytic system, the present study is dealing with its prior use as a rapid “research tool” for exploring the effect of K promoter on the catalytic system under consideration. Subsequently, the insight obtained from EP studies is applied to the design of conventional catalysts' composites, i.e. Pd/γ-Al2O3 catalysts conventionally promoted by K at loadings indicated from EP studies. For the system investigated, the optimal promoter loading was in the range of ∼ 0.45–0.55, in terms of K-coverage. In this range of K-loadings significant enhancement on de-N2O activity was obtained under reducing conditions using both methods of K-promotion. However, in the presence of excess oxygen in the reaction mixture the effect of K-promotion was less pronounced, independently of the reducing agent used. Παρουσιάστηκε στο: Solid State Ionics

The electrochemical reduction of nitrous oxide and oxygen has been studied on cone-shaped electrodes of La 1− x Sr x FeO 3− δ perovskites in an all solid state cell, using cyclic voltammetry. It was shown that the activity of the La 1− x Sr x FeO 3− δ perovskites for the electrochemical reduction of nitrous oxide mainly depends on the amount of Fe(III) and oxide ion vacancies. The activity of the La 1− x Sr x FeO 3− δ perovskites towards the electrochemical reduction of nitrous oxide is much lower than the activity of the La 1− x Sr x FeO 3− δ perovskites towards the electrochemical reduction of oxygen, making the possibility of electrochemically reducing nitrous oxide selectively in an exhaust gas containing excess oxygen on this type of materials very doubtful.

A 0.5 wt.% Pt/TiO2 catalyst was prepared and used for the low-temperature selective catalytic reduction (SCR) of NO with C3H6 in the presence of excess oxygen. The effects of Pt loading and O2 concentration on Pt/TiO2 catalytic performance for low-temperature SCR were investigated. It was found that optimal Pt loading was 0.5 wt.% and excess O2 favored low-temperature SCR of NOx. The mechanism of low-temperature SCR of NO with C3H6 was investigated with respect to the behavior of adsorbed species over Pt/TiO2 at 150 degrees C using in situ DRIFTS. The results indicated that surface nitrosyl species (Ptdelta(+)-NO and Ti3(+)-NO) and Pt2(+)-CO are main reaction intermediates during the interactions of NO, C3H6 and O2. A simplified NO decomposition mechanism for the low-temperature SCR of NO with C3H6 was proposed.

Selective catalytic reduction of NO by hydrogen was studied over Cr modified Pt/ZSM-35 catalysts. The preparation process greatly influenced catalytic activity and sample prepared by co-impregnation method exhibits the best activity. In situ DRIFT studies revealed that on Pt–Cr/ZSM-35, (1) new Pt-NO δ+ and NO species adsorbed on Pt were detected upon NO + O 2 adsorption; (2) much more ammonia species were formed under reaction condition. Cr addition not only enhanced the adsorption of NO x but also promoted the formation of surface NH 4 + species, which should be the origin of promotional effect of Cr on Pt/ZSM-35 for H 2 -SCR reaction.

Excess oxygen and 1-at% Mg co-doped CuScO 2 [3R](0001) epitaxial films were prepared on a-plane sapphire substrates by combining two-step deposition and post-annealing techniques. The optical and electrical transport properties of the co-doped epitaxial films were compared with those of the CuScO 2 [3R](0001) epitaxial films. No significant increase in optical absorption was observed in the co-doped epitaxial films, and the energy gap for direct allowed transition was estimated at 3.7 eV. The carrier concentration of CuScO 2 [3R](0001) epitaxial films was controlled from ~ 10 16 cm - 3 to ~ 10 18 cm - 3 at room temperature by adjusting the excess oxygen and Mg co-doping. The electrical conductivity, carrier concentration, and Hall mobility of the most conductive film were 3.6 × 10 - 2 Scm - 1 , 8.5 × 10 17 cm - 3 and 2.6 × 10 - 1 cm 2 V - 1 s - 1 at room temperature, respectively. The temperature dependence of the electrical transport properties of the film exhibited semiconducting characteristics, and the activation energy estimated from the temperature dependence of the carrier concentration was 0.50 eV.

A new concept of a novel “dual bed” configuration of NH 3 and CO-SCR catalytic system (NH 3 -CO-SCR), comprising Cu/Beta as top catalyst bed for NH 3 -SCR and WO 3 /Ir/SiO 2 as bottom catalyst bed for CO-SCR, is described in this article. The combined catalytic system provides high NO reduction efficiency, in a broad temperature range (160–600 °C). The NO conversion over the combined catalytic system reached up to 98% between 280 and 320 °C, as compared to the system using only Cu/Beta or WO 3 /Ir/SiO 2 with sole NH 3 or CO as reductant. Furthermore, the combined catalytic system shows high NO reduction efficiency even in the presence of lower concentrations of NH 3 and CO. Thus, the potential advantage of this combined system is that it can effectively reduce NO during situations when NH 3 and CO concentration is expected to fluctuate in real driving conditions which could potentially lead to NH 3 and CO slip issues.

A series of TiO 2 supported catalysts with 0.5 wt% noble metal (Pt, Pd, Rh and Ru) were used for the low-temperature selective catalytic reduction (SCR) of NO with propylene in the presence of excess oxygen. Under an atmosphere of 150 ppm NO, 150 ppm C 3 H 6 and 18 vol% O 2 (GHSV 72,000 h −1 ), the Pt/TiO 2 was found to be the most active catalyst giving a complete C 3 H 6 conversion and 63% NO x reduction simultaneously at 140 °C. The enhanced activity of Pt/TiO 2 may be associated to its outstanding activities in the temperature-programmed oxidation (TPO) of NO to NO 2 and C 3 H 6 to CO 2 .

Superconductive La2CuO4+delta with T-c similar to 40 K has been obtained by chemical oxidation using NaClO solution. The oxygen-decrease processes have been studied during the thermal treatment processes at different temperatures. The material separates into discrete phases with different transition temperatures for samples treated at 100 degrees C consistent with the oxygenation process reported previously. However, Tc decreases continuously in samples treated at 300 degrees C, similar to the superconducting properties of La2-xSrxCuO4. In addition, the coexistence of superconducting and antiferromagnetic phases cannot be observed in our samples. The interrelation between the transition temperature and the treatment conditions such as temperature and time is discussed. (c) 2005 Elsevier B.V. All rights reserved.

The correlation between the oxygen partial pressure, p(O 2 ), at the annealing process after heat treatment (post-annealing) and the J c value at 4.2 K in 10 T is investigated for Bi-2212/Ag tapes and Bi-2212 single crystal. The p(O 2 ) was controlled in the range from 0.01 to 14.5 atm, and high oxygen-pressure post-annealing was performed for the samples by using an autoclave furnace. The J c -B characteristics of Bi-2212/Ag tape were found to depend strongly on the condition of post-annealing; the optimum condition of post-annealing for obtaining a Bi-2212/Ag tape with the highest J c value is considered to be the p(O 2 ) 6 atm at 300 °C. The improvement of the J c value by post-annealing under the condition of p(O 2 ) < 6 atm is considered to be due to the decrease in the electromagnetic anisotropy that occurs as a consequence of the change in the excess oxygen content of the Bi-2212 phase. On the other hand, it is assumed that the degradation of the J c value by higher oxygen-pressure post-annealing is the result of the deterioration of the T c value. It suggests that the delicate balance between the decrease in the electromagnetic anisotropy and the deterioration of the T c by over-doping should be optimized for the improvement of the Bi-2212/Ag tapes.

Kinetics of natural gas reburning is modeled on the basis of GRI3.0 and the method of Gear. The calculation results indicate that the model agrees with experiments. HCN, NHi and HCCO play an important role in the reburning system. Injecting NH3 and increasing the fraction of HCCO in the reburning system will promote NO reduction. Injecting natural gas at the places wherein the fraction of NO is highest is a benefit to de-NOx. There exists an optimal value of ratio of natural gas: NO for reburning system. The influences of temperature, excess oxygen ratio and pressure are also discussed in the reburning system. D 2004 Elsevier B.V. All rights reserved.

Pd (0.1 wt.%)/Al2O3 catalyst was found to be active for the selective NO reduction employing H2 (NO conversion>90%) under excess O2 at low temperatures (110–190 °C) with good N2 selectivity (about 70%). The selectivity towards N2O was sensitive to the reaction conditions and decreased as the temperature was raised. The maximum selectivity to NH3 occurred at 190 °C. The selectivity to N2O was inhibited greatly by O2 at low temperatures. Gaseous O2 promoted the selectivity to N2 as well as the generation of adsorbed NH species in comparison to the reactions without O2. In situ diffuse reflectance IR spectroscopy (DRIFTS) measurements suggested that there was competition between H2 and other adsorbed species such as nitrates and water at low temperatures, and the rate determining step may be the adsorption and activation of H2 over the catalyst.

The roles of aliovalent Ca(II)-for-Y(III) substitution and high-pressure-oxygen annealing in the process of "superconducterizing" the Co-based layered copper oxide, CoSr2(Y1-xCax)Cu2O7+d (Co-1212), were investigated. The as-air-synthesized samples up to x = 0.4 were found essentially oxygen stoichiometric (-0.03, 16 pages, 6 figures, submitted to Solid State Communications

Selective catalytic reduction (SCR) of N 2 O with C 3 H 8 over FeZSM-5 under excess oxygen is strongly inhibited by NO. The assistance of the hydrocarbon in N 2 O reduction vanishes at high partial NO pressures, approaching the activity of the N 2 O + NO system at molar NO/N 2 O ratios of 1.5–2, with N 2 O/C 3 H 8 =1. This effect differs from the NO promotion in direct N 2 O decomposition over Fe-zeolite catalysts. The negative effect of NO on the N 2 O reduction has a significant impact in the design and operation of catalytic reactors in tail-gases of nitric acid plants and other sources where NO comes along with N 2 O.

A small landmark trial in 1952 showed that excess oxygen use might well be causing a major epidemic of retinal blindness in preterm babies. That a single study of just 65 babies was enough to throw doubt on a long-standing treatment strategy revealed just how powerful a tool the randomized controlled trial could be. Confirmatory evidence from a cooperative trial involving a further 212 babies banished all residual doubt just 4 years later, and it remains a major reproach that we have still not learnt, after 50 years, how to optimize the delivery of oxygen to the preterm baby with further help from this powerful tool. Two well-conducted trials have recently shown that avoiding subclinical hypoxaemia (fractional SaO(2)92%) in babies more than a month old does nothing to improve later growth or development. It is now time the same question was asked of babies less than a month old, because we might reduce their need for ventilatory support. This is particularly important in babies of less than 28 weeks' gestation, who remain, currently, at serious risk of chronic lung disease and permanent retinal scarring.

We have successfully synthesized polycrystalline bulk samples of La 2 CuO 4 with the Nd 2 CuO 4 -type (T′) structure at low temperatures. First of all, La 2 CuO 4 with the K 2 NiF 4 -type (T) structure was prepared by the conventional solid-state reaction. Secondly, La 2 CuO 3.5+ δ with the Sr 2 CuO 3 -type structure was obtained by heating mixed powder of T-La 2 CuO 4 and CaH 2 at 175 °C in an evacuated Pyrex tube. Thirdly, T′-La 2 CuO 4+ δ was prepared by heating La 2 CuO 3.5+ δ at 250 °C in air. Finally, T′-La 2 CuO 4+ δ was reduced using CaH 2 to remove excess oxygen. The powder X-ray diffraction pattern has revealed that the product is of the single phase of T′-La 2 CuO 4 , but no superconductivity has been observed at T > 2 K in the magnetic susceptibility measurement. The residual excess oxygen may suppress the appearance of superconductivity.

The green emission of lead tungstate (PbWO4) is closely related to structure defects. For studying the mechanism of the green emission, the local structure of PbWO4 has been first investigated by extended X-ray absorption fine structure using synchrotron radiation. The results indicate that the excess oxygen in air-annealed PbWO4 exists and forms "WO4 + O-i" centers. The green emission of PbWO4 is not caused by (WO3 + F) centers, but probably originates from the centers Of "WO4 + O-i". (C) 2001 Elsevier Science B.V. All rights reserved.

The effect of SO2 for the selective reduction of NO by C3H8 on Ag/Al2O3 was investigated in the presence of excess oxygen and water vapor. The NOx conversion decreased permanently even in the presence of a low concentration of SO2 (0.5–10 ppm) at

The presence of SO 2 had a considerable effect to increase the activity of Ir/SiO 2 catalyst for NO reduction with H 2 in the presence of excess oxygen, although NO reduction in the absence of SO 2 was completely unselective. Similar SO 2 promoting effect was also observed for NO reduction with CO or C 3 H 6 . Silica was found to be the best support for iridium.

The tunability of the oxygen stoichiometry in the Ba RE (Cu 0.5 Fe 0.5 ) 2 O 5+ δ double-perovskite structure, stable with rare earth elements RE =Lu–Pr, was studied by both normal-pressure thermogravimetric oxidative (O 2 ) and deoxidative (Ar) post-annealings and high-pressure heat treatments carried out in a cubic-anvil-type high-pressure apparatus. Under reducing conditions the Ba RE (Cu 0.5 Fe 0.5 ) 2 O 5+ δ double perovskite is obtained at δ ≈0 irrespective of the size of the RE constituent. In the structures with RE =Pr and Nd the oxygen stoichiometry can be continuously varied by normal-pressure post-annealings up to δ ≈0.24 and 0.35, respectively, whereas with a smaller rare earth ion, i.e., RE =Lu–Sm, the amount of excess oxygen raises from δ ≈0 only upon high-pressure heat treatment.

We have prepared the superconducting La 2 CuO 4+ δ electrochemically oxidized at 333 K. Each sample is a single-phase superconductor; the low- T c phase ( T c =32 or 36 K, oxidation time=24 h, δ =0.068) or the high- T c phase (45 K, 72 h, 0.093). We have studied the relation between the hole concentration n H , determined by the Hall effect measurement as n H ≡1/ eR H and the valence of Cu 2+ p , determined by the iodometric titration in La 2 CuO 4+ δ . In highly oxidized La 2 CuO 4+ δ , the p /2-dependence of n H has been found to be different from that of the ordinary (La 1− x Sr x ) 2 CuO 4 . Similar phenomena were observed in (La 1− x Sr x ) 2 CuO 4+ δ ( x =0.050, 0.075, 0.100) electrochemically oxidized at 333 K. These results suggest that in La 2 CuO 4+ δ or (La 1− x Sr x ) 2 CuO 4+ δ , the intercalated excess oxygen plays a different role in conduction from Sr in the ordinary (La 1− x Sr x ) 2 CuO 4 .

Selective reduction of NO by CH4 on an In–Fe2O3/H-ZSM-5 catalyst was investigated in the presence of excess oxygen. Compared with In/H-ZSM-5, the In–Fe2O3/H-ZSM-5 catalyst with high Fe2O3 contents showed higher activity in a wide range of reaction temperatures. It was found that the addition of Fe2O3 yielded a promotion effect on CH4 activation. The influence of water vapor on NO conversion was also investigated. The activity of the In/H-ZSM-5 catalyst has been found to be strongly inhibited by water vapor, while the In–Fe2O3/H-ZSM-5 catalyst remained fairly active in the presence of 3.3% steam.

Photoluminescence (PL) study of needle-like ZnO nanorods grown under standard and oxygen-rich conditions is presented. The yellow-orange band at ~580nm increases with excess oxygen during growth. Subsequent annealing in a reducing atmosphere shows the disappearance of this band. The yellow-orange emission is attributed to oxygen interstitials (O"i).

The structure of a La 2 CuO 4+ y single crystal with the excess oxygen content y =0.03 has been studied by means of neutron diffraction at T =13 K. Although the extra oxygen content of y =0.03 is inside the miscibility gap of La 2 CuO 4+ y (0.01 y Cmca symmetry. It was confirmed that the extra oxygen, O4, is located close to the site (1/4, 1/4, 1/4). The structural parameters for all atoms lay between those previously determined for the oxygen-poor and oxygen-rich phases representing the edges of the miscibility gap, y =0.01 and 0.06, respectively. Our data allow us to conclude that (1) the phase-separated and non-phase-separated La 2 CuO 4+ y compounds are structurally identical, and (2) the crystal structure of La 2 CuO 4+ y changes monotonically when the extra oxygen content changes from 0 to 0.05.

Radiation damage in Bi2Sr2CaCu2O8+δ or Bi(2 2 1 2) by 55 MeV Li3+-beam has been studied from electrical resistivity and X-ray diffraction characterizations. This irradiation increases electrical resistivity and broadens X-ray diffraction lines by generating defects in all samples. But superconducting critical temperature, Tc, is seen to increase for Bi(2 2 1 2) with excess oxygen and decrease for Bi(2 2 1 2) with O-content less than the optimum, that gives maximum Tc. This increase of the superconducting critical temperature on Li-irradiation of O-rich Bi(2 2 1 2) as well as the decrease for low-O Bi(2 2 1 2) is due to O-displacement. This is in agreement with our earlier He-irradiation results.

Polycrystalline samples of Bi 2 Sr 2− x La x CaCu 2 O y and pure Bi2212 with different oxygen content have been prepared and studied by Raman spectroscopy. No frequency change of O Bi A g mode is observed. The O Sr A g mode exhibits remarkable downward frequency shift. The analysis indicates that the content of excess oxygen inserted into the Bi 2 O 2 layer is the important factor causing frequency shift of the O Sr A g mode.

A “nonstoichiometry” mechanism of giant isotope effects in colossal-magnetoresistance manganites and other oxide semiconductors is proposed. It is not related to an anomalously strong electron-phonon coupling in them and is based on the fact that the thermodynamic equilibrium densities of the oxygen vacancies or excess oxygen atoms depend on the mass of the oxygen atom. As the vacancies and excess atoms act as donors and acceptors, respectively, the charge carrier density in oxide semiconductors is isotope dependent. On the other hand, as nonstoichiometric oxygen atoms produce an effective pressure inside the crystal, the difference in the effective pressures for different isotopes can manifest itself as an isotope dependence of their electric and magnetic properties.

Powder of BaPb x Bi y O z with strictly controlled compositions were synthesized over a wide composition range of x and y . The region where the superconductivity appears to coincide with that of pseudo-cubic structure. In the superconducting phase, the oxygen content was found to exceed 3.00 suggesting that the excess oxygen plays an important role in realizing the superconductivity.

CuMOR catalysts with different Si/Al ratios and copper contents, prepared from the acid and sodium forms, were studied in NO reduction with propene in the presence of excess oxygen. It was observed that the influence of zeolite Si/Al ratio on CuMOR catalytic activity for NO SCR by propene depends on the catalyst copper content, the reverse being also true. For mordenites prepared from the acid form, it was shown that the most active catalyst must have ∼60% of copper exchange, whereas for those prepared from the sodium form, the maximum catalytic activity is obtained for catalysts with 20% of copper exchange. Moreover, it was observed that at low copper-exchange levels, the catalyst prepared from the sodium form exhibits much higher activity than those prepared from the acid form. Although, when the copper-exchange level increases, the effect of zeolite form is less pronounced. Thus, it was indicated that Bronsted acidity does not promote the NO selective reduction by propene.

Thin, discontinuous Pt/Ti films with different film thicknesses on microfabricated conductometric sensors were exposed to ppm levels of hydrogen or propylene at elevated temperatures in the presence of excess oxygen. Exposure to hydrogen at temperatures between 100 and 400°C resulted in a decrease in film resistance, with a trend towards higher response with increasing temperature. Thinner Pt/Ti films (35 A Pt on 65 A Ti) showed larger relative resistance changes than thicker Pt/Ti films (75 A Pt on 65 A Ti). Neither of the films were sensitive to propylene until the temperature exceeded 350°C, coinciding with the onset of catalytic oxidation of propylene. Above 350°C, the film resistance decreased with increasing propylene concentration. Thus, operating the films in different temperature regimes permits differentiation between hydrogen and propylene. Reversible sensor response can be accomplished in the presence of excess gas phase oxygen.

Over the past decade, we have studied in detail the low-energy spin fluctuations in :a 2− x Sr x CuO 4 for x between 0 and 0.18. Our experiments, as well as those by others, have revealed a fascinating interplay between the hole doping, the static and dynamic spin fluctuations and superconductivity. Recently, using electrochemical techniques, we have learned how to produce large single crystals of La 2 CuO 4+ y which are relatively homogenous. In this latter system, the dopants are characterized by annealed rather than quenched disorder. Furthermore, we have demonstrated staging behavior of the excess oxygen analogous to staging in intercalated graphite. We have now succeeded in carrying out measurements of the low-energy spin fluctuations in stage-6 La 2 CuO 4+ y . Specifically, we find that in this system which has T c = 31 K, the spin fluctuations are incommensurate with energy and temperature dependencies very much like those in La 1.85 Sr 0.15 CuO 4 with T c = 33 K. In addition, we find that T c / δ is a constant for high-quality materials in both La 2− x Sr x CuO 4 and La 2 CuO 4+ y , here δ is the incommensurability.

The excess oxygen concentrations of La2NiO4+δhave been measured in 0.00–6.06, 13.33–18.25, or 66.66–71.40 kPa of oxygen in the range 300–1273 K by the desorption method. The electrical conductivities of La2NiO4+δhave been also measured in 1.33, 13.33, 66.66, or 101.33 kPa of oxygen in the range 77.4–1273 K or under a helium atmosphere (1 atm) in the range 77.4–300 K. The mechanism of the metal–semiconductor transition of La2NiO4+δis discussed on the basis of the excess oxygen concentration and the electrical conductivity data. The metal–semiconductor transition of La2NiO4+δis explained by the carrier concentration and the activation energy changes associated with the incorporation of excess oxygen.

X-ray structure analyses were performed with HgBa2CuO4+δ and Hg1−xPbxBa2CuO4+δ single crystals. The onset of the superconducting transition of the crystals ranges from 78–92 K. Hg-1201 crystallizes with space group P4/mmm and has lattice pafameters a = 3.8907(2) A and c = 9.556(1) A . The structure was refined to R = 0.023 (wR2 = 0.036) in the ideal 1201 type with an excess oxygen content of 6(2)% and an occupancy of 97% at the Hg site. Pb-doping decreases the lattice parameters to a = 3.8836(2) A and c = 9.553(1) A , and the refinement converged at R = 0.042 (wR2 = 0.088). Pb atoms are shifted by 0.5 A to (0.14, 0, 0) and the excess oxygen atom O(3) by 0.45 A to (0.38, 1 2 , 0). It has not a well defined position in the lattice, but is distributed randomly in a ring-like configuration around the ( 1 2 , 1 2 , 0) site, supporting a Pb clustering model. Rather high anisotropic temperature factors U11 and U22 of Hg and apical O(1) atoms are observed, which are also present in higher members of the Hg(Pb)-12(n − 1)n series. They are discussed in terms of corrugated OHgO bonds. Comparison with other structure refinements of 1201 shows a correlation of the transition temperature with the position of the Ba atom, which seems to be a good indicator for the hole doping evel in 1201.

A study of the magnetic properties of La 2 Cu 1 − x Zn x O 4 + δ (0 ≤ x ≤ 0.13; δ = 0.02) by means of magnetization measurements ( M vs T , H ) is reported. The Neel temperature of the 3D antiferromagnetic order (AF) is found to decrease with Zn substitution much more rapidly than in samples without excess oxygen. The effect of Zn substitution on the metamagnetic M vs. H transition is discussed, analyzing the temperature dependence of both the critical field H c and the weak ferromagnetic moment M s for different compositions x .

Magnetic states in tetragonal La2NiO4+δ (δ = 0.156, 0.181, 0.186) single crystals with excess oxygen in peroxide form have been investigated. Temperature dependence of the magnetization is found to be anisotropic in all cases of excess oxygen content. The magnetizationa parallel to the c-axis after zero field cooling show a cusp around 20 K in contrast to the Curie—Weiss-like magnetization perpendicular to the c-axis. A spin glass state is suggested below 20 K after field cooling and relaxation behavior in the magnetization. The origin of spin-freezing in La2NiO4+δ with excess oxygen in peroxide form is discussed.