Catalytic decomposition of H2O2 on Co3O4 doped with MgO and V2O5

The effects of doping of Co₃O₄with MgO (0.4–6 mol%) and V₂O₅ (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H₂O₂ at 30–50°C. Pure and doped samples were prepared by thermal decomposition in air at 500–900°C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V₂O₅ doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co₃O₄ solid. Treatment of Co₃O₄ with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H₂O₂ decomposition, of Co₃O₄ was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant (k) measured at 40°C on Co₃O₄ due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V₂O₅-doping of Co₃O₄ brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40°C over the 0.75 mol% V₂O₅-doped Co₃O₄ solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO³⁺–CO²⁺ ion pairs and created Mg²⁺–CO³⁺ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H₂O₂. V₂O₅-doping exerted an opposite effect via decreasing the number of CO³⁺–CO²⁺ ion pairs besides the possible formation of cobalt vanadate.     

Cu2(bipy)2V6O17: A new type of layered inorganic–organic hybrid copper(II) vanadate

Hydrothermal reaction of copper(II) acetate, 2,2′-bipyridine (bipy) and NH₄VO₃ at 170 °C lead to a new layered polyoxovanadate with organically covalent-bonded copper(II) complex, Cu₂(bipy)₂V₆O₁₇ (1). Cu₂(bipy)₂V₆O₁₇ (1) is a new copper(II) vanadium(V) oxide featuring a new layered architecture, in which the V₂O₇ dimeric units and the cyclic tetranuclear V₄O₁₂ cluster units are interconnected via corner sharing into a unique one-dimensional {V₆O₁₇}⁴⁻ anionic chain, such chains are further bridged by {Cu(bipy)}²⁺ complex cations into a 010 organic–inorganic hybrid layer.     

Hydrothermal syntheses and crystal structures of bimetallic cluster complexes [{Cd(phen)2}2V4O12]·5H2O and [Ni(phen)3]2[V4O12]·17.5H2O

The hydrothermal reactions of vanadium oxide starting materials with divalent transition metal cations in the presence of nitrogen donor chelating ligands yield the bimetallic cluster complexes with the formulae [{Cd(phen₂)₂V₄O₁₂]·5H₂O (1) and [Ni(phen)₃]₂[V₄O₁₂]·17.5H₂O (2). Crystal data: C₄₈H₅₂Cd₂N₈O₂₂V₄ (1), triclinic. a=10.3366(10), b=11.320(3), c=13.268(3) Å, =103.888(17)°, β=92.256(15)°, γ=107.444(14)°, Z=1; C₇₂H₁₃₁N₁₂Ni₂O_29.5V₄ (2), triclinic. a=12.305(3), b=13.172(6), c=15.133(4), =79.05(3)°, β=76.09(2)°, γ=74.66(3)°, Z=1. Data were collected on a Siemens P4 four-circle diffractometer at 293 K in the range 1.59° <θ<26.02° and 2.01°<θ<25.01° using the ω-scan technique, respectively. The structure of 1 consists of a [V₄O₁₂]⁴⁻ cluster covalently attached to two {Cd(phen)₂}²⁺ fragments, in which the [V₄O₁₂]⁴⁻ cluster adopts a chair-like configuration. In the structure of 2, the [V₄O₁₂]⁴⁻ cluster is isolated. And the complex formed a layer structure via hydrogen bonds between the [V₄O₁₂]⁴⁻ unit and crystallization water molecules.     

Soft chemistry synthesis of the perovskite CaCu3Ti4O12

The perovskite CaCu₃Ti₄O₁₂ (CCT) has been obtained after calcination of oxalate precursors at 900–1000 °C in air. Those precursors are prepared using a soft chemistry method, the coprecipitation. The oxalate powders consist of disk-like particles of 2–3 μm diameter and 300–400 nm thickness. By varying the ratio of the initial amounts of metal chlorides, additional phases (CaTiO₃, TiO₂ and CuO) could be obtained besides CCT. The corresponding multiphased ceramics present improved dielectric properties.     

Gaseous nitryl azide N4O2: A joint theoretical and experimental study

Gaseous nitryl azide N₄O₂ is generated by the heterogeneous reaction of gaseous ClNO₂ with freshly prepared AgN₃ at −50 °C. The geometric and electronic structure of the molecule in the gas phase has been characterized by in situ photoelectron spectroscopy (PES) and quantum chemical calculations. The experimental first vertical ionization energy of N₄O₂ is 11.39 eV, corresponding to the ionization of an electron on the highest occupied molecular orbital (HOMO) {4a″(π_{nb(N4–N5–N6)})}⁻¹. An apparent vibrational spacing of 1600 ± 60 cm⁻¹ (ν_asO1N2O3) on the second band at 12.52 eV (π_{nb(O1–N2–O3)}) further confirms the preference of energetically stable chain structure in the gas phase. To complement the experimental results, the potential-energy surface of this structurally novel transient molecule is discussed. Both calculations and spectroscopic results suggest that the molecule adopts a trans-planar chain structure, and a five-membered ring decomposition pathway is more favorable.     

Solid state synthesis and characterization of iron（Ⅱ） pyrophosphate Fe2P2O7

Offwhite pure Fe_2P_2O_7 was synthesized through solid phase reaction using Fe_2O_3 and NH_4H_2PO_4 in argon atmosphere.The reaction products of Fe_2O_3 and NH4_H_2PO_4 at a series of temperatures from 400 to 900℃were characterized by XRD.Comparison and analysis of XRD patterns of resultant products indicated well-crystallized Fe_2P_2O_7 could be obtained over 630℃and Fe_2P_2O_7 prepared at 700℃was triclinic in cell type.Comparison of the cell parameters proved that the as-prepared Fe_2P_2O_7 belonged toβ- Fe_2P_2O_7 in crystal phase and SEM showed its size distribution was 0.5-2μm.     

V_2O_5/Ti-Ce-PILC在H_2S选择性催化氧化过程中的催化性能

合成了TiO_2-CeO_2柱撑黏土负载V_2O_5催化剂,通过XRD、氮气吸附脱附、TG、FT-IR、H_2-TPR、NH_3-TPD、XPS等方法对其物理化学性质进行了表征,研究了该催化剂在H2S选择性催化氧化反应中的活性。结果表明,负载5%V_2O_5的TiO_2-CeO_2柱撑黏土在180℃下催化效果最好,且尾气中不含SO_2。V_2O_5、TiO_2和CeO_2之间的相互作用提高了催化剂的活性,CeO_2提高了催化剂的热稳定性,同时提供大量晶格氧,加强了V_2O_5的氧化还原作用,降低了反应温度;TiO_2加强了VO_x和CeO_x的再氧化,降低了硫酸盐的覆盖率,从而降低了催化剂的失活速率。     

Thermal solid–solid interactions and physicochemical properties of NiO/Fe2O3 system doped with K2O

The effects of calcination temperature and doping with K₂O on solid–solid interactions and physicochemical properties of NiO/Fe₂O₃ system were investigated using TG, DTA and XRD techniques. The amounts of potassium, expressed as mol% K₂O were 0.62, 1.23, 2.44 and 4.26. The pure and variously doped mixed solids were thermally treated at 300, 500, 750, 900 and 1000 °C. The catalytic activity was determined for each solid in H₂O₂ decomposition reaction at 30–50 °C. The results obtained showed that the doping process much affected the degree of crystallinity of both NiO and Fe₂O₃ phases detected for all solids calcined at 300 and 500 °C. Fe₂O₃ interacted readily with NiO at temperature starting from 700 °C producing crystalline NiFe₂O₄ phase. The degree of reaction propagation increased with increasing calcination temperature. The completion of this reaction required a prolonged heating at temperature >900 °C. K₂O-doping stimulates the ferrite formation to an extent proportional to its amount added. The stimulation effect of potassium was evidenced by following up the change in the peak height of certain diffraction lines characteristic NiO, Fe₂O₃, NiFe₂O₄ phases located at “d” spacing 2.08, 2.69 and 2.95 Å, respectively. The change of peak height of the diffraction lines at 2.95 Å as a function of firing temperature of pure and doped mixed solids enabled the calculation of the activation energy (ΔE) of the ferrite formation. The computed ΔE values were 120, 80, 49, 36 and 25 kJ mol⁻¹ for pure and variously doped solids, respectively. The decrease in ΔE value of NiFe₂O₄ formation as a function of dopant added was not only attributed to an effective increase in the mobility of reacting cations but also to the formation of potassium ferrite. The calcination temperature and doping with K₂O much affected the catalytic activity of the system under investigation.     

Anaerobic oxidation of isobutane: Catalytic properties of MgV2O6 and Mg2V2O7 prepared by the molten method

The catalytic activity of MV₂O₆ and M₂V₂O₇ type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO₂ were formed by every catalyst tested. The activities for isobutene formation were CuV₂O₆ > ZnV₂O₆, NiV₂O₆, CoV₂O₆ > MgV₂O₆ > MnV₂O₆  CaV₂O₆. Isobutene was a major product over M₂V₂O₇ (MM). Co₂V₂O₇ showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co₂V₂O₇ is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg₂V₂O₇ (MM) improved the activity. It is shown by the oxidation at low O₂ concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO₂ formation by the oxygen species derived from molecular oxygen in the gas phase.     

Thermal stability of osmium mixed oxides I. CaOsO3 decomposition products: A new orthorhombic phase Ca2Os2O7

The thermal decomposition of CaOsO₃ by differential thermal analyses, thermogravimetry and X-ray powder diffraction has been studied. In nitrogen CaOsO₃ decomposes at 880 ± 10°C into CaO, osmium metal and oxygen due to the reaction CaOsO₃ → CaO + Os + O₂. In static air the decomposition occurs in three stages: 2CaOsO₃ + 1/2O₂ → Ca₂Os₂O₇ (in region 775–808°C), Ca₂Os₂O₇ → Ca₂Os₂O_6,5 + 1/4O₂ (at a temperature interval of 850–1000°C) and in the third stage Ca₂Os₂O_6,5 → 2CaO + OsO₄ ÷ 1/4 O₂ (at 1005 ± 5°C). The first intermediate Ca₂Os₂O₇ is isostructural with orthorhombic Ca₂Nb₂O₇ and its cell parameters are: a₀ = 3.745 Å, b₀ = 25.1 Å, c₀ = 5.492 Å, Z = 4, space group Cmcm or Cmc2. Ca₂Os₂O₇ exhibits metallic conductivity and its electrical resistivity is 4.6 × 10⁻² ohm-cm at 296K.     

Factors influencing decomposition of H2O2 over supported Pd catalyst in aqueous medium

Since H₂O₂ decomposition can result in selectivity/yield loss in the direct H₂O₂ synthesis process from H₂ and O₂ over supported Pd catalysts, it is important to have an enhanced understanding about the factors affecting the H₂O₂ decomposition reaction. Herein, detailed studies have been undertaken to investigate the influence of different factors, such as (a) nature and concentration of acid in reaction medium, (b) nature and concentration of halide in presence and absence of acid in reaction medium, (c) pretreatment procedures and (d) catalyst modification by incorporation of different halides, on the H₂O₂ decomposition reaction over a 5% Pd/C catalyst in aqueous medium at 25 °C. This study has shown that the H₂O₂ decomposition activity is profoundly influenced by all the above factors. The effectiveness of the acids in suppressing the H₂O₂ decomposition activity decreased in the following order: hydroiodic acid > hydrobromic acid > hydrochloric acid  acetic acid > phosphoric acid > sulfuric acid > perchloric acid. The ability of the acid to decrease the H₂O₂ decomposition activity was found to very strongly depend on the nature of its associated anion. Halides, such as iodide, bromide and chloride were particularly effective in suppressing the H₂O₂ decomposition activity. Oxidation pretreatment of the catalyst was found to strongly suppress its H₂O₂ decomposition activity, while a reduction treatment was found to promote its activity. A gradual decrease in the H₂O₂ decomposition activity of the catalyst was observed with each successive usage due to in situ sub-surface oxidation of Pd by H₂O₂. Halide incorporation either via the reaction medium or prior catalyst modification had a similar qualitative effect on the H₂O₂ decomposition activity.     

Fabrication of Nb2O5/C nanocomposites as a high performance anode for lithium ion battery

Nb₂O₅/C nanosheets are successfully prepared through a mixing process and followed by heating treatment.Such Nb₂O₅/C based electrode exhibits high rate performance and remarkable cycling ability, showing a high and stable specific capacity of ~380 mAh g^-1 at the current density of 50 mA g^-1(much higher than the theoretical capacity of Nb₂O₅).Further more,at a current density of 500 mA g^-1,the nanocomposites electrode still exhibits a specific capacity of above 150 mAh g^-1 after 100 cycles.These results suggest the Nb₂O₅/C nanocomposite is a high performance anode material for lithium-ion batteries.     

The first tetranuclear vanadium(V) peroxo complex: Preparation, vibrational spectra and X-ray crystal structure of K6[V4O4(O2)8(PO4)]·9H2O

The vanadium(V) peroxo phosphato complex K₇[V₄O₄(O₂)₈(PO₄)]·9H₂O has been obtained from the KVO₃---KH₂PO₄---KOH---H₂O₂---H₂O---C₂H₅OH system. The X-ray structural analysis revealed a tetranuclear anionic structure in which two dinuclear [V₂O₂(O)₂)₂(μ-η¹ : η²-O₂)₂] units are connected by the μ₄-PO₄ group.     

γ-Al2O3对SCR脱硝催化剂V2O5-WO3/TiO2的改性研究

采用溶胶凝胶法制备了不同γ-Al₂O₃含量的钛铝复合载体,以此为载体采用浸渍法负载V₂O₅和WO₃制备了一系列催化剂。采用X射线衍射(XRD)、比表面积测定(BET)、程序升温还原(H₂-TPR)、高分辨率透射电子显微镜(HRTEM)等表征技术对催化剂表面形态进行分析,同时在模拟氨气选择性催化还原NO(NH₃-SCR)的反应条件下,对催化剂的脱硝反应活性和SO₂抗中毒进行考察。结果发现,TiO₂和γ-Al₂O₃之间的协同作用使得V₂O₅-WO₃/TiO₂-γ-Al₂O₃催化剂的脱硝效率及活性窗口明显优于单一载体制备的催化剂,表现出了良好的热稳定性和抗SO₂毒化能力,特别是V₂O₅-WO₃/TiO₂-15% γ-Al₂O₃在310~460 ℃,NO的转化率均在80%以上,反应窗口最宽。各种表征结果表明,TiO₂-γ-Al₂O₃复合载体中γ-Al₂O₃高度分散在TiO₂上,复合载体具有较大的比表面积,同时具有较强的还原能力。     

Heat capacities of the tungsten oxides WO3, W20O58, W18O49 and WO2

The heat capacities of the tungsten oxides WO₃, W₂₀O₅₈, W₁₈O₄₉ and WO₂ have been measured over the temperature range 340–999 K using differential scanning calorimetry. The lower oxides were prepared by controlled reduction of WO₃ in H₂/H₂O gas atmospheres. Previous calorimetric work on WO₃ is confirmed in the temperature range 340–800 K, however, significant increases in heat capacity were observed in the range 800–999 K prior to the orthorhombic—tetragonal phase transition. W₂₀O₅₈ is shown to behave similarly to WO₃. A high temperture phase change is evident, however, this appears to be complete by 970–990 K. The measured values of heat capacity for W₁₈O₄₉ are in close agreement with estimated data for W₁₈O₄₉. There is no evidence of any phase transitions for this oxide in the temperature range studied. The heat capacity data for WO₂ confirm previous drop calorimetry measurements and give no evidence of any phase changes for WO₂ in the temperature range 340–990 K.     

纳米负载型V2O5-WO3/TiO2催化剂碱中毒及再生研究

实验制备了陶瓷颗粒为骨架的纳米级V₂O₅-WO₃/TiO₂(C)催化剂。采用浸渍法模拟碱金属中毒,研究了中毒及再生对催化剂脱硝活性的影响,运用XRD、FT-IR、H₂-TPR、XPS技术表征分析了碱金属对催化剂的失活作用。实验表明,碱金属能使催化剂活性降低,钾的毒性大于钠。FT-IR结果显示,催化剂以Lewis酸作为活性酸位。H₂-TPR、XPS结果表明,钾的加入降低了催化剂的氧化能力,主要影响了催化剂表面的吸附氧。采用单纯的水洗方法并不能提高催化剂活性,而酸洗再生后催化剂在较高反应温度下活性得到较好的恢复。     

燃煤烟气中砷对V_2O_5-WO_3/TiO_2 SCR脱硝催化剂性能的影响

通过将商业V_2O_5-WO_3/TiO_2脱硝催化剂暴露于含As_2O_3烟气中,制备了砷中毒催化剂,并运用X射线衍射(XRD)、比表面积(BET)、NH3化学吸附、傅里叶变换红外光谱(FT-IR)、X射线光电子能谱等技术表征分析了砷对催化剂性能的影响,并提出了催化剂砷中毒机理。结果表明,砷对催化剂具有严重的毒害作用,As_2O_3会吸附在催化剂表面,并被催化剂氧化形成As_2O_5覆盖层,减小催化剂比表面积,减少催化剂V活性位,阻止催化剂对NH3的吸附,造成催化剂失活。     

Preparation of crack-free ZrO2 membrane on Al2O3 support with ZrO2–Al2O3 composite intermediate layers

To develop porous alumina supported MF ZrO₂ membranes, ZrO₂–Al₂O₃ composite intermediate layers are considered in order to decrease stress creation during the processing and avoid cracks formation. The relation between distortion stress and sintering shrinkage was experimentally studied. And the cracks formation mechanism was qualitatively evaluated and discussed. Finally, crack-free YSZ membrane with pore size of 0.16 μm on the two ZrO₂–Al₂O₃ intermediate layers possessing a gradient composition was successfully prepared and characterized.     

1.54 and 1.75 μm infrared luminescence of Y2O3:Er

A new 1.75 μm infrared emission transition of Y₂O₃:Er³⁺ is assigned to the ⁴S_3/2 → ⁴I_9/2 transition of Er³⁺ ions situated at the C₂ sites of cubic RE₂O₃ (RE = Y, Gd, Lu). The intensities of features in the 1.54 μm ⁴I_15/2–⁴I_13/2 absorption transition due to Er³⁺ at S₆ and C₂ sites are consistent with the site occupation ratio and the relative magnetic dipole–electric dipole intensity contributions of Er³⁺ at the different sites. The 1.54 μm emission lines are predominantly from Er³⁺ ions at C₂ sites. The different behaviours of the emission intensities 1.75 and 1.54 μm groups with change in Er³⁺ dopant ion concentration, preparation technique, Yb³⁺ co-doping, temperature change and different excitation line are rationalized.     

Kinetics and mechanisms of the reduction of Cu0.5Zn0.5Fe2O4 with hydrogen at 400–600 °C for the production of metallic nanoparticles

Ferrites have continued to attract attention over years. As magnetic materials, ferrites cannot be replaced by any other magnetic material because they are relatively inexpensive, stable and have a wide range of technological applications in transformer core, high quality filters, high frequency circuits and operating devices. Nanocrystallite sizes of Cu_0.5 Zn_0.5Fe₂O₄ with 25 nm have been obtained by hydrothermal route. Cu_0.5Zn_0.5Fe₂O₄ powder was isothermally reduced in H₂ flow at 400–600 °C. The reduction behavior of the produced powder as well as the influence of reduction temperature on the structural characteristics of the products was extensively studied. Microstructure of partially and completely reduced samples was investigated and the activation energy values were calculated from Arrhenius equation. The activation energy for nanocrystallite Cu_0.5 Zn_0.5Fe₂O₄ reduced at the initial stage was found to be 37.4 kJ/mole, while that at the final stage is 14 kJ/mole. The approved mathematical formulations for the different crystallite sizes gas solid reaction were applied and it was found that at the final stages the reaction is controlled by the gaseous diffusion while the combined gaseous diffusion and interfacial chemical reaction is the rate controlling mechanisms at the initial stages. The reduction process produce nanoparticles metallic phases of iron, copper and zinc, which have ball and fibers shapes.