A novel nonaqueous route to V2O3 and Nb2O5 nanocrystals

The reaction between transition metal alkoxides and benzyl alcohol provides a novel soft chemistry route to metal oxide nanoparticles. The method allows the preparation of nanocrystals of two important transition metal oxides, namely V₂O₃ and Nb₂O₅. Although the reaction temperatures of 200–220 °C are comparably low, the obtained particles are highly crystalline. According to TEM investigations, the V₂O₃ crystals exhibit particle sizes between 20 and 50 nm, and the Nb₂O₅ crystals display platelet-like particle shapes with sizes of 50–80 nm, without any indications of amorphous character.     

纳米复合材料Ag/MxOy-TiO2(MxOy=ZnO、Al2O3和Fe2O3)的制备及其微波辅助光催化降解甲基橙

采用溶胶-凝胶-程序升温溶剂热一步法,利用表面活性剂EO₂₀PO₇₀EO₂₀(P123)作为模板剂,分别制备了三元纳米复合材料Ag/ZnO-TiO₂、Ag/Al₂O₃-TiO₂和Ag/Fe₂O₃-TiO₂。通过XRD、氮气吸附-脱附测定、TEM以及扫描电子显微镜配合X-射线能量色散谱仪(SEM-EDS)等对合成的3种催化剂进行了对比表征分析。结果表明,复合材料Ag/M_xO_y-TiO₂中Ag以单质形式存在并较好地分布在M_xO_y-TiO₂表面上。所合成产物颗粒尺寸较小(约10 nm左右),形貌较好。其中,Ag/ZnO-TiO₂的比表面积与Ag/Al₂O₃-TiO₂十分相近,略大于Ag/Fe₂O₃-TiO₂。光催化活性研究中,以甲基橙为模型分子且辅以微波场作用。结果显示,上述三元复合材料的活性均明显高于未掺杂银的二元复合材料,其中Ag/ZnO-TiO₂的光催化活性最好,在90 min内对甲基橙的降解率高达86%。     

Synthesis of morphology-controllable mesoporous Co3O4 and CeO2

Recently, extensive works have been devoted to the morphology control of mesoporous materials with respect to their use in various applications. In this paper, we used two kinds of mesoporous silica, SBA-15 rods and spheres as hard templates to synthesize morphology-controllable mesoporous metal oxides. By carefully controlling the loading of metal precursors in the mesopores of the hard template, mesoporous Co₃O₄ and CeO₂ with different morphologies, such as micrometer-sized rod, hollow sphere, saucer-like sphere, and solid sphere were conveniently obtained. The structural properties of these materials were characterized by XRD, BET, SEM and TEM. In addition, it is found that the differences observed in the textural properties of the two mesoporous metal oxides nanocasted from the same template can be attributed to the properties of metal precursors and the interaction between metal oxide and SiO₂. Thus-obtained mesoporous metal oxides with such special morphologies may have a potential application in the field of environmental catalytic oxidation.     

Plasma afterglow atomization in electrothermal atomic absorption spectrometry

Potentialities of an Ar/H₂ microwave induced plasma afterglow at 8.2 mbar as an atomization source in electrothermal atomic absorption spectrometry have been examined. More specifically the atomization efficiency, as shown from appearance temperatures, and the reaction mechanisms of the atomization of the oxides and chlorides of alkaline earth and transition metals have been investigated and compared with conventional electrothermal atomization. For all the investigated metal chlorides and alkaline earth oxides, a considerable decrease in appearance temperature (some 500 K), is observed in the plasma afterglow. Such enhanced atomization is believed to be linked to reactions with H atoms. No plasma enhancement, however, is measured for the atomization of the transition metal oxides. All metal oxides are effectively reduced to free metal in the solid state by the Ar/H₂ afterglow, and as a consequence the supply rate is governed by the metal sublimation for these compounds. For metal chlorides, however, strong evidence is found for the atomization process to proceed via gas phase reactions.     

MnOx-SnO2 Catalysts Synthesized by a Redox Coprecipitation Method for Selective Catalytic Reduction of NO by NH3

MnO_x-SnO₂ composite oxides prepared by a redox coprecipitation route were tested in selective catalytic reduction of NO by NH₃ at low temperatures. The results showed that the MnO_x-SnO₂ catalyst with a Mn/(Mn+Sn) molar ratio of 75% exhibited the best performance, on which NO conversion of 100% could be achieved at temperatures of 120–200 °C. The characterization results of N₂ adsorption-desorption, X-ray diffraction, and X-ray photoelectron spectroscopy indicated that the higher surface area, the formation of solid solution between manganese and tin oxides, and the high oxidation state manganese species were responsible for the high catalytic activity of the MnO_x-SnO₂ catalyst.     

Magnetic properties of Ca2F2-xMnxO5

Magnetic susceptibility of Ca₂F_2-xMn_xO₅ members crystallizing in two different structures, one having octahedral (O), tetrahedral (T) and square-pyramidal (SP) coordination of transition metal atoms (OTSP structure) and the other having octahedral and tetrahedral coordination (OT structure), has been investigated. Susceptibility behaviour of the oxides with OTSP structure is different from that of the oxides with OT structure. Ca₂Fe_1-33Mn_0-67O₅ with OTSP structure shows an antiferromagnetic ordering while the corresponding oxide with OT structure shows weak ferromagnetism. Contribution No. 398 from the Solid State and Structural Chemistry Unit     

MgF2 as a non-conventional catalyst support

This review reports progress in the study of the surface structure of MgF₂ and its use as a support of catalytically active phases. Magnesium fluoride was applied first as a support in catalysis for systems containing individual oxides of transition metals (Mo, V, W, Cu, Cr) and then two different oxide phases (Cu-Cr, Cu-Mn), a metal phase (Ru, Pd) or heteropolyacids. Its use as a support enabled determination of the structure and surface properties of these catalysts. The MgF₂-supported catalysts are characterized by high activity and selectivity in such processes as: hydrodechlorination of chlorofluorocarbons (CFCs), hydrodesulfurization of organic compounds and purification of fuel combustion products from nitrogen oxides. Magnesium fluoride has been also used in MgF₂-doped chromium or aluminum fluoride catalysts for Cl/F exchange on hydrochlorocarbons.     

Effective modification of MgO with surface transition metal oxides for NF3 decomposition

NF3 decomposition over transition metal oxides coated MgO reagents in the absence of water is investigated. The results show that NF3 can be decomposed completely over pure MgO but the time of NF3 steady full conversion kept as short as 80 min, while the reactivities of coated MgO reagents were remarkably enhanced by transition metal oxides, for example the time of NF3 complete conversion over 12%Fe/MgO extended to 380 min. It is suggested that not only an increase in surface area but also a significant enhancement in the fluorination of MgO substrate caused by the surface transition metal oxides result in an improved reactivity of coated MgO reagents for NF3 decomposition.     

Basicity and catalytic activity of ZrO2?Y2O3 mixed oxides in the oxidation of cyclohexanol

Acidity/basicity of mixed oxides of ZrO₂−Y₂O₃ activated at various temperatures were determined by a titration method using Hammett indicators. The activity of these oxides towards liquid phase oxidation of cyclohexanol are also reported. The activity data parallel the basicity of these oxides.     

Tetragonal paramagnetic complex in Gd3+ doped Nd2(SO4)3·(NH4)2SO4·8H2O au]V.M. Malhotra

EPR studies of Gd³⁺ doped in single crystals of Nd₂(SO₄)₃·(NH₄)₂SO₄·8H₂O (hereafter referred to as NASO) at room (RT) and liquid nitrogen (LNT) temperatures exhibit that (1) the metal aquo complex has a tetragonal symmetry with abnormally low magnitudes of crystalline field parameters at RT and (2) NASO undergoes a possible phase transition between RT and LNT.     

酸性金属氧化物对锰铈氧化物催化剂脱硝温度窗口的调控作用

利用溶胶-凝胶法,采用三种酸性金属氧化物（氧化铌、氧化钨和氧化钼）对锰铈复合氧化物催化剂进行了改性. 测试了催化剂的氮氧化物选择性催化还原（SCR）活性,以筛选对应不同温度窗口的合适酸性氧化物改性剂. 同时评价了催化剂的NO氧化和NH₃氧化活性. 利用X射线衍射、BET比表面积测试、H₂程序升温还原、NH₃/NO_x程序升温脱附和NH₃/NO_x吸附红外光谱等手段对催化剂进行了表征. MnO_x-CeO₂催化剂表现出良好的低温（100-150 ℃）活性. 酸性金属氧化物的添加削弱了催化剂的氧化还原特性,从而抑制了NH₃的活化和NO₂辅助的快速SCR反应. 与此同时,相对高温（250-350 ℃）区NH₃的氧化也受到了抑制,B酸和L酸上的NH₃吸附得以增强. 因此,催化剂的SCR脱硝温度窗口向高温移动,改性效果Nb₂O₅ < WO₃ < MoO₃.     

L3/L2 white-line intensity ratios in the electron energy-loss spectra of 3d transition-metal oxides

The L₃/L₂ white-line intensity ratio in transition-metal oxides deviates widely from the statistical value of 2 : 1 but shows interesting systematics. In a series of oxides of a given metal, the ratio reaches a maximum for the d⁵ configuration (e.g. MnO) and a minimum for the d⁰ configuration (e.g. KMnO₄). In a series of monoxides, sesquioxides and dioxides of different metals, the ratio is again a maximum at the d⁵ configuration and decreases as the configuration changes towards d⁰ or d¹⁰. Our results, obtained by electron energy-loss spectroscopy, carried out in an electron microscope, are interpreted on an atomic mechanism involving spin-spin coupling. According to this model, the L₂ transition probability decreases in the progression d⁰ to d⁵ whereas the L₃ transition probability decreases beyond d⁵.     

Polymorphism in Bi2WO6

The polymorphism of Bi₂WO₆ has been studied using differential dilatometry and differential thermal analysis with polycrystalline specimens prepared by sintering the oxides Bi₂O₃ and WO₃. Two reversible polymorphic transitions were observed, one at 662°C and one at 962°C. The former transition showed a very small change of enthalpy and very little dimensional change, while the latter showed a large thermal hysteresis, had a large change of enthalpy, and was accompanied by a sizable volume change. The high-temperature powder X-ray data indicated that the intermediate phase as well as the low-temperature form had orthorhombic symmetry and the high-temperature form had monoclinic symmetry. The 662°C transition is displacive and the 962°C transition reconstructive. A crystal structure of the high-temperature form is proposed and discussed in comparison with that of the low-temperature form.     

Continuous hydrothermal synthesis of CoFe2O4 nanoparticles

We have investigated the continuous hydrothermal synthesis and crystallization of spinel CoFe₂O₄ via the reaction of ferric nitrate and cobalt nitrate with sodium hydroxide. The reaction was carried out in water at temperatures ranging from 475 to 675 K and pressures of 25 MPa. The relative solubility of the precipitating cations was found to play a critical role in attaining the correct product. It was found necessary to control pH and temperature in order to prevent premature precipitation of iron in the reactor. Two variations of the continuous hydrothermal technique were examined—cold mixing and hot mixing. The cold mixing experiments produced a product with less impurity than the hot mixing experiments. Furthermore, the cold mixing configuration was successful in producing uniform nanoparticles of CoFe₂O₄. A mechanism of particle formation was postulated involving the precipitation of metal hydroxides at ambient conditions, dissolution of the hydroxides as temperature is increased followed by rapid precipitation of metal oxides at elevated temperatures. The hot mixing experiments, on the other hand, simply involve the precipitation of metal oxides due to the addition of the hot hydroxide solution. In both cases, very fine particles of CoFe₂O₄ are produced in the range of the processing conditions investigated.     

New Selenidogermanates with Transition-Metal Complexes as Counterions: Solvothermal Synthesis, Crystal Structures, and Properties of [Mn(en)3]2Ge2Se6 and [Fe(dien)2]2Ge2Se6

Summary. New selenidogermanates [Mn(en)₃]₂Ge₂Se₆ (en = ethylenediamine) and [Fe(dien)₂]₂Ge₂Se₆ (dien= diethylenetriamine) were synthesized by the reaction of germanium dioxide, elemental selenium, and transition metal chlorides in respectively en and dien. Both compounds crystallize in the monoclinic space group P2₁/n with two formula units in the unit cell, and consist of discrete [Ge₂Se₆]⁴⁻ anions with transition metal complex cations as counter ions. The [Ge₂Se₆]⁴⁻ anion is formed by two GeSe₄ tetrahedra sharing a common edge to form a planar Ge₂Se₂ four-membered ring. The [Mn(en)₃]²⁺ and [Ni(dien)₂]²⁺ complex cations are in distorted octahedral geometry. In both selenidogermanates extensive N–H···Se hydrogen bonding contacts lead to 3-dimensional network structures. The band gaps of 2.36 and 2.25 eV were derived from optical absorption spectra. Thermogravimetric analysis shows that the first compound decomposes in two steps under the nitrogen stream, while the second exhibits a one-step decomposition process.     

CdCu3(OH)6Cl2: A new layered hydroxide chloride

A new transition metal hydroxide chloride containing kagomé layers of magnetic ions, CdCu₃(OH)₆Cl₂, has been synthesized and structurally characterized. The actual low symmetry P2₁/n structure can be derived from the ideal trigonal one with a change in cation distribution and coherent distortions of the anion framework. The result is a fundamentally different Cu²⁺ kagomé framework than found in the related Herbertsmithite and Kapellasite minerals. Magnetization measurements show no transition to long range magnetic order above T=2 K, despite strong antiferromagnetic interactions with a Weiss temperature of θ_w=−150 K. Furthermore, we show that the structure of CdCu₃(OH)₆Cl₂ and related hydroxide chlorides can be rationalized on the basis of [(OH)₃Cl]⁴⁻ pseudopolyatomic anions that pack and rotate, in much the same way as do traditional polyatomic anions. This opens the door to rational design of new and useful hydroxide chloride materials.     

Formation,dissociation and expansion behavior of platinum group metal oxides (PdO,RuO2, IrO2)

The oxidation behavior of palladium, ruthenium and iridium powders of different grain sizes was investigated by TG, DTA and X-ray methods. The solid oxides formed during heating up (PdO, RuO₂, IrO₂) show different stability and decomposition temperatures depending on the oxygen pressure. The kinetics of the reaction MeO_x → Me+x/2 O₂ is discussed. High temperature X-ray studies confirmed the strong anisotropy of thermal expansion in the case of RuO₂ and IrO₂. The thermal expansion behavior of these oxides is compared to that of other rutile-type oxides.     

ZrxTixAl1-2xO2的制备及其在三效催化剂上的应用

Zr_0.5Ti_0.5O₂(ZT) and Zr_0.25Ti_0.25Al_0.5O₂(ZTA) mixed oxides were prepared by co-precipitation method and characterized by low temperature adsorption-desorption， XRD and NH₃-TPD. The activity of Pt/Zr_0.5Ti_0.5O₂ and Pt/ Zr_0.5Ti_0.5Al_0.5O₂ catalysts was evaluated using the simulated gases. The results show that ZTA samples exhibit higher specific surface area， larger pore volume and proper surface acidic amount and acidity in comparison with ZT. The results of the catalytic test indicate that Pt/ZT and Pt/ZTA catalysts exhibit excellent low-temperature catalytic activity and lower light-off temperatures of hydrocarbon， carbon monoxide and nitrogen oxides， especially better conversion for nitrogen oxides (NO_x). The addition of Al₂O₃ into ZT enhanced the anti-aging property of Pt/ ZTA catalysts due to the excellent textural， structural， surface acidity and thermal stability.     

Solubility of trans-Co2(CO)6 [3,5-bis(CF3)C6H3P(i-C3H7)2] in dense carbon dioxide

The title compound (1) was prepared by the reaction of 3,5-bis(CF₃)C₆H₃P(i-C₃H₇)₂ (L1) and Co₂(CO)₈. Its solubility in supercritical carbon dioxide was measured at varying temperatures and pressures using a modified analytical extraction device. Solubility data were determined in the temperature and pressure ranges between 40 and 70 °C and between 100 and 300 bar, respectively. The solubility of 1 is lower compared to (p-CF₃C₆H₄)₃P, but much higher than for transition metal complexes bearing phosphines without fluorinated substituents.     

35Cl NQR and 1H NMR studies of [C(NH2)3]AuCl4, [C(NH2)3]2PtCl4, and [C(NH2)3]2PdCl4

The temperature dependence measurements of ³⁵Cl NQR frequencies and ¹H NMR spin-lattice relaxation time T₁ were carried out for guanidinium tetrachloro-aurate(III), -platinate(II), and -palladate(II). The gold(III) complex showed four NQR lines at various temperatures between 77 and 344 K, while the platinum-(II) and palladium(II) complexes gave two NQR lines in the temperature ranges 77–169 K and 77–220 K, respectively. An unusual phase transition was located at 363 K for the gold(III) complex. The high-temperature phase was easily supercooled. All the complexes studied yielded a T₁ minimum attributable to the reorientation of the planar cation about its C₃ axis. The motional parameters were evaluated. The Zeeman-quadrupole cross relaxation between protons and chlorine nuclei was observed for the platinum(II) and palladium(II) complexes at various temperatures below room temperature, while it was also detected for the high-temperature phase of the gold(III) complex.