Electrochemical reduction of NO on La2-x Sr x NiO4 based electrodes

The series La_2 − x Sr _x NiO₄ (x = 0.0, 0.05, 0.15, 0.25, 0.35, and 1.0) was tested for functionality as electrode materials for direct electrochemical reduction of NO. The materials were tested using cyclic voltammetry in 1% NO and 10% O₂ in Ar on a cone-shaped electrode. The best materials for the electrochemical reduction of NO are La₂NiO₄ and LaSrNiO₄, which have current densities for NO reduction 1.82 and 7.09 times higher, respectively, than for O₂ at 400 °C. Increasing the temperature decreased the ability to reduce NO before O₂ while the activity increased. The adsorbed species during direct decomposition was attempted, clarified using X-ray absorption near-edge structure experiments and thermogravimetry, but no conclusive results were obtained.     

The thermal behaviour of the hydroxide mixtures used for the synthesis of MgFe2O4 spinel

The thermal behaviour of hydroxide mixtures, precursors to the synthesis of MgFe₂O₄ spinel powders, was investigated.The mixtures of hydroxides were prepared by coprecipitation reaction from nitrate solutions with an Mg/Fe atomic ratio of 12. The results were related to the thermal behaviour of separately precipitated components of the hydroxide mixtures. Samples prepared by mechanically mixing the separately precipitated hydroxides were also studied.The spinel formation temperature was identified by performing XRD analysis on powder samples heated to different temperatures. The presence of spinel from the thermal decomposition of coprecipitated mixtures was detected at a temperature as low as 380°C. The separate formation of MgO and Fe₂O₃ from the thermal decomposition of mechanical mixtures was observed; nevertheless the formation of MgFe₂O₄ through a solid state reaction between the oxides was noted at a temperature as low as 500°C.The Authors wish to thank Dr. L. Petrilli and Mr. F. Dianetti for carrying out the elemental chemical analyses at the Microanalysis Service of the C. N. R. laboratories of the Area della Ricerca di Roma.     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

Rhodium–Aluminum-Mixed Oxide Catalysts for Selective Reduction of NO x by Hydrocarbons

Rhodium—alumina-mixed oxides have been investigated as catalysts for selective catalytic reduction of NO _x by propene, as a part of the R&D Project of Next Generation Catalysts Research Institute. The results indicated that the NO _x reduction activity increases with a decrease in the reducibility of rhodium, suppressing wasteful consumption of propene by the reaction with oxygen. Coprecipitation method for the preparation of Rh-alumina catalysts was effective for the formation of the less-reducible rhodium sites, and the addition of zirconium and gallium further enhanced the formation of those sites and increased the selectivity of NO _x reduction.     

NiCr x Fe2-x O4 as cathode materials for electrochemical reduction of NO x

Solid solutions of spinel-type oxides with the composition NiCr _x Fe_2-x O₄ (x = 0.0, 0.5, 1.0, 1.5, 2.0) were prepared with the glycine–nitrate combustion synthesis. Four-point DC resistivity measurements show an increase in the conductivity as more Cr is introduced into the structure, whereas dilatometer measurements show that the linear thermal expansion decreases with increasing Cr content. The oxides were used as electrode materials in a pseudo-three-electrode setup in the temperature range of 300–600 °C. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrochemical behavior in 1% NO, 1% NO₂, and 10% O₂. NiCr₂O₄ shows high activity in NO and NO₂ relative to O₂ and can therefore be considered as a possible electrode material. Peaks were detected in the voltammograms recorded on NiCr₂O₄ in 1% NO. The origin of the peaks seems to be related to the oxidation of Cr or the formation of nitrogen-containing species formed on the surface of the electrode.     

NOx储存催化剂Pt/BaAl2O4-Al2O3的XAFS研究

采用共沉淀-浸渍法在不同载体焙烧温度下,制备了不同Al/Ba原子比的Pt/BaAl2O4-Al2O3系列样品.用XRD, XANES, EXAFS,以及NSC (NOx storage capacity）测定等手段对样品的微观结构和NOx储存性能进行了详细的表征.样品中Ba物种是以BaAl2O4和BaCO3两种混合物相的形式存在,且伴随着载体焙烧温度和Ba含量的降低, BaAl2O4物相的分散度变高, NOx储存活性也随之提高,这表明BaAl2O4相的分散度与样品的NOx储存性能密切相关,小颗粒的BaAl2O4相是NOx的主要储存活性中心.在样品中, Pt物种以金属原子簇形式存在,分散度很高,其Pt－Pt壳层配位数较标样Pt粉有显著下降, Pt－Pt键长变短,出现了纳米收缩现象.高分散的小颗粒金属Pt原子簇为捕获和氧化NOx的主要活性中心.     

Effect of FeO x on the electrocatalytic properties of NiCo2O4 for O2 evolution from alkaline solutions

Mixtures of NiCo₂O₄ and FeO _x were obtained by thermal decomposition of the nitrates of Ni, Co, and Fe in appropriate proportions. Two series of electrodes were prepared: (1) at constant composition (20 mol% FeO _x ) and various calcination temperatures in the range 200 to 480 °C and (2) at constant calcination temperature (300 °C) and various compositions in the whole composition range 0 to 100 mol% FeO _x . The oxide layers were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry. Experimental data showed that the layers consist of a mixture of phases in which Fe oxide is present as Fe₂O₃. The electrocatalytic properties were assessed by means of quasi-stationary potentiostatic current-potential curves for the O₂ evolution reaction from alkaline solution. Results have shown that the mechanism of O₂ evolution depends on composition moderately. The electrocatalytic activity appears to depend on composition only slightly. Dedicated to Professor Oleg Petrii on the occasion of his 70th birthday on August 24th, 2007.     

Overview on the selective lean NO x reduction by hydrocarbons over Pt-based catalysts

Selective catalytic reduction of NO _x with hydrocarbons (HC-SCR) has received much attention as one of potential technologies for reducing NO _x emissions under lean-burn conditions. Pt/ZSM-5 prepared by sublimation method and Pt/V/MCM-41 catalysts have been introduced for the wider activity temperature window than those Pt catalysts reported previously. The influence of pre-treatment, oxygen concentration, water and SO₂ on the activities of Pt-based catalysts has been discussed. Combinatorial catalysis, which has been developed recently for discovering the practical HC-SCR catalysts quickly, has been introduced too. Finally, the reaction mechanism of HC-SCR over Pt-based catalysts has been briefly discussed.     

Cathodic materials for lithium-ion batteries based on spinels Li x Mn2−y Me y O4: Synthesis, phase composition, and structure of Li x Mn2−y Cr y O4 at x = 1.0−1.2 and y = 0−0.5

Extralithiated chromium-doped finely divided lithium-manganese spinels are synthesized as a result of a two-step solid-phase process with use made of the fusion-saturation method. The spinels are intended for application as cathodic materials in lithium-ion batteries. The phase composition and structural characteristics of samples of cathodic materials of the type Li _x Mn_2?y Cr _y O₄ are studied. The samples with x = 1.0?1.2 and y = 0?0.5 are characterized by phase purity and cubic syngony with parameter a = 0.817?0.823 nm and a disperseness equal to 1–2 nm. The maximum content of chromium and lithium in Li _x Mn_2?y Cr _y O₄ that does not lead to violation of cubic syngony is determined. Lithium excess in the cathodic material that does not exceed 0.2 formula units may be used for compensating the irreversible capacity. Replacing some manganese atoms by chromium may facilitate retention of the structures’s integrity in the course of cycling.     

MgFe2O4@SiO2-PrNH2/Pd/bimenthonoxime core-shell magnetic nanoparticles as a recyclable green catalyst for heterogeneous Suzuki cross-coupling in aqueous ethanol

Magnetically recoverable MgFe₂O₄@SiO₂-PrNH₂/Pd/bimenthonoxime nanoparticles were prepared and characterized by SEM, EDX, TEM, XRD, XPS, ICP, VSM and FT-IR. The nanocatalyst was used for Suzuki cross-coupling in aqueous ethanol media, and the corresponding biaryl derivatives were synthesized within short reaction time. The catalyst was separated by an external magnet and reused several times.

     

NiFe_2O_4/NiO纳米复合材料的制备及电催化水氧化性能

以镍铁水滑石为单一前驱体,通过高温焙烧制备了NiFe_2O_4/NiO纳米复合材料,对该纳米复合材料在碱性介质中电催化水的氧化性能进行了研究.结果表明,相比于化学共沉淀法制备的单独NiFe_2O_4、NiO及其物理混合物NiFe_2O_4+NiO,NiFe_2O_4/NiO纳米复合材料具有更高的电催化水氧化活性和更好的循环稳定性.电流密度为10 m A/cm2时过电位仅为364 m V.     

Crystal structure refinement of basic tellurium nitrate: A reformulation as (Te2O4H)+(NO3)−

Basic tellurium nitrate crystallizes in the space group Pnma witha=14.607 (1),b=8.801 (1), andc=4.4633 (4) Å. Full-matrix least-squares refinement of automatic diffractometer data converged to a residualR=0.036 (R _w =0.046) for 899 independent reflections. A detailed analysis of the structural data leads us to reformulate this compound as (Te₂O₄H)⁺(NO₃)^– with a basic structural element consisting of a charged two-dimensional puckered Te₂O₄H⁺ network with discrete NO₃ ^– anions, an example of apositively-charged network structure.

---

Verfeinerung der Kristallstruktur von basischem Telluriumnitrat. Eine Umformulierung in (Te₂O₄H)⁺(NO₃)^–

Zusammenfassung Basisches Telluriumnitrat kristallisiert in der Raumgruppe Pnma mita=14,607 (1),b=8,801 (1) undc=4,4633 (4) Å. Die verfeinernde Auswertung der Diffraktometerdaten konvergierte zuR=0,036 (R _w =0.046) für 899 unabhängige Reflexe. Eine detaillierte Analyse der Strukturdaten führte zu einer Umformulierung dieser Verbindung als (Te₂O₄H)⁺(NO₃)^–, wobei die Basisstruktur aus einem geladenen, zweidimensionalen, gefalteten Te₂O₄H⁺ Netzwerk mit getrennten NO₃ ^– Anionen besteht. Es stellt dies ein Beispiel einerpositiv geladenen Netzstruktur dar.

     

Preparation of Silicates Using HSi(OC2H5)3 and Their NO x -Adsorption Behavior

The preparation and NO-adsorption/desorption behavior of Li, Ca and Ba silicates were investigated aiming at the application to a NO_x-absorbent. Li silicate was prepared by reaction of HSi(OC₂H₅)₃ with aqueous lithium silicate solution (LSS). Ca and Ba silicates were prepared from gels obtained using CH₃Si(OC₂H₅)₃, Si(OC₂H₅)₄, HSi(OC₂H₅)₃ and alkaline-earth alkoxides. The surface of these silicates indicated the solid basicity of H₀ = 9 and adsorbed the acidic gas of NO. FT-IR spectra of the silicates adsorbing NO showed the absorption peaks in the range of 1300–1600 cm^{– 1} corresponding to ionic and covalent nitrate NO₃^–. The complete desorption of adsorbed NO species occurred above 500°C in the Li silicate, above 500°C in the Ca and Ba silicates prepared using CH₃Si(OC₂H₅)₃, and above 700°C in the Ba and Ca silicates prepared using Si(OC₂H₅)₄. Regarding the Ca and Ba silicates, the difference in siloxane structure is thought to cause the difference in adsorption state and desorption behavior of NO.     

Thermal reduction and reoxidation of spinel-type Cu1−xZnxAl2O4

The thermochemical reactivity of the spinel-type quaternary metal oxide Cu_1–xZn_xAl₂O₄ has been investigated for different Cu:Zn ratios. In oxygen or inert gas atmospheres no considerable reduction is observed. In molecular hydrogen metal selective reduction of the Cu is found at relatively high temperature. The solid reduction product is made up of sintered, poorly dispersed metallic copper on a Zn-Al-O metal oxide support, a potential catalyst for the methanol synthesis. Owing to the measured high reduction temperature leading to the mentioned sintering of the metallic copper, the activity of this system cannot be high.Financial support by the Swiss National Science Foundation under project Nr. 2027933.89 is gratefully acknowledged.     

Physical properties and electrochemical performance of LiMn2O4 cathode materials prepared by a precipitation method

LiMn₂O₄ powder for lithium-ion batteries was prepared by a precipitation method, and the effects of calcination temperature on the physical properties and electrochemical performance of the samples were investigated by various methods. The results of X-ray diffraction (XRD) showed that the lattice parameter (a) and the unit cell volume (v) decrease with the increasing calcination temperature, and the LiMn₂O₄ sample calcined at 750°C has smaller particle size and higher crystallinity than other samples. The results of the electrochemical experiments showed that the sample calcined at 750°C has larger peak currents, higher initial capacity, and better cycling capability, because of its lower charge-transfer resistance and larger diffusion coefficient of Li⁺ ions than those of other samples.     

Electronic structures of superconductors YBa2Cu3−x M x O y (M=Sn,Ni)

Based on the EHMO approach, the energy band structures for superconductors YBa₂Cu_3–x Sn _x O _y (y>7) and YBa₂Cu_3–x Ni _x O_y (y<7) were calulated in the present paper. The influence of the cation doping at the Cu site in the unit cell and the oxygen content on their electronic structures was studied. The results showed that the cation doping at the Cu site resulted in the great decreases in the bandwidths of the broad anisotropic Cu-O bands and the densities of states. In YBa₂Cu_3–x Sn _x O _y , however, these decreases are compensated by the increase in the oxygen content caused by the Sn-doping, which results in a small change in the total densities of states. For YBa₂Cu_3–x Ni _x O _y , the effect of the doping on its electronic structures in dominant. The Ni-doping, therefore, results in a great change in the electronic structures. In addition, the study on the projected densities of states of the Ni-doped system revealed that the 2D Cu-O planes in the Y-Ba-Cu-O system played a dominant role in superconductivity.     

CrOx-CeO2二元氧化物表面NO的NH3催化还原反应机理

利用原位漫反射红外光谱法研究了473 K下在CrOx-CeO2二元氧化物表面NO的NH3催化还原反应的机理。研究了CrOx-CeO2二元氧化物表面在反应过程中的表面吸附物种。为了更加清晰的了解反应过程,在SCR反应过程中分别切断NH3和NO的气流,并采集了所生成的原位漫反射红外光谱图,通过研究以上结果得出结论:当前状态下的SCR反应过程可能服从ER机理。     

Oxidation and Reduction Processes During NO x Removal with Corona-Induced Nonthermal Plasma

In this paper, the NO-to-NO ₂ conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO _x removal experiments in N ₂ +NO _x and N ₂ +O ₂ +NO _x gaseous mixtures, it is supposed that the reverse reaction NO ₂ +ONO+O ₂ may not only limit NO ₂ production in N ₂ +NO _x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NON ₂ +O, induce negligible NO removal provided the O ₂ concentration is larger than 3.6%. With adding H ₂ O into the reactor, the produced NO ₂ per unit removed NO can be significantly reduced due to NO ₂ oxidation. NH ₃ injection could also significantly decrease the produced NO ₂ via NH and NH ₂ - related reduction reactions. Almost 100% of NO ₂ can be removed in gaseous mixtures of N ₂ +O ₂ +H ₂ O+NO ₂ with negligible NO production.     

CrOx-CeO2二元氧化物表面NO的NH3催化还原反应机理

利用原位漫反射红外光谱法研究了473 K下在CrOx-CeO₂二元氧化物表面NO的NH₃催化还原反应的机理。研究了CrO-CeO₂二元氧化物表面在反应过程中的表面吸附物种。为了更加清晰的了解反应过程, 在SCR反应过程中分别切断NH₃和NO的气流, 并采集了所生成的原位漫反射红外光谱图, 通过研究以上结果得出结论:当前状态下的SCR反应过程可能服从E-R机理。     

Preparation of spinel ferrite NiFe2O4 fibres by organic gel-thermal decomposition process

Functional spinel ferrite fibers are attractive for high-tech applications. The spinel NiFe₂O₄ fibres have been successfully prepared by the organic gel-thermal decomposition process from raw materials of Ni, Fe nitrate salts and citric acid. The gel spinning performance was a major factor for preparation of uniform gel fibrous precursors. The gel spinnability was related to the citrate-metal complex structure and linear-type structural molecules [(C₆H₆O₇)₄NiFe₂]_n for the gel precursor was possibly formed during the complexation reaction between the citric acid and metal ions at pH 5. The composition, structure of the gel precursors and products derived from thermal decomposition of these precursors were characterized by FTIR, XRD, and SEM. The thermal decomposition process of the gel precursors was investigated by TG-DSC. The prepared spinel NiFe₂O₄ fibres having grain sizes of 60–70 nm were featured with diameters of about 1 μm, and aspect ratios up to 10⁶ (length/diameter).