Synthesis and properties of MoO3/ZrO2 solid acid catalysts for the preparation of polydimethylsiloxane (PDMS) via octamethylcyclotetrasiloxane (D4) ring-opening

A series of MoO₃/ZrO₂ catalysts were prepared by impregnation method, and characterized by X-ray diffraction (XRD), specific surface area (BET) and temperature-programmed desorption of NH₃ (NH₃-TPD). The polydimethylsiloxane (PDMS) was prepared by ring-opening polymerization from D₄ and MM with MoO₃/ZrO₂ catalysts. The effects of MoO₃/ZrO₂ catalysts preparation conditions on PDMS molecular weight and reaction conversion rate were discussed. Moreover, the effects of reaction conditions on the ring-opening polymerization were also studied. During the preparation of PDMS, the molecular weight of the product can be controlled by adjusting the mass ratio of D₄:MM. The MoO₃/ZrO₂ catalyst was compared with other catalysts during the ring-opening process, and the repeated times of MoO₃/ZrO₂ catalysts were also studied. The results showed that MoO₃/ZrO₂ catalyst had more excellent catalytic performance, for ring-opening process, and when the repeated times was more than 5, the catalytic activity decreased significantly. In addition, the kinetics of D₄ ring-opening polymerization with the MoO₃/ZrO₂ catalyst was investigated.     

Reactivity investigations of some chosen peroxo-vanadium(V), manganese(III) and chromium(VI) compounds

An interpretative account of the results of reactions in aqueous medium of a highly peroxygenated vanadium(V) complex, K [V(O_{2 3}]·3H₂O, with different organic and inorganic substrates is presented. The reactions were monitored by solution EPR spectroscopy and isolation of products at different stages of the reactions. Redox reactions between diperoxide, K[VO(O₂)₂(H₂O)] and VOSO₄ were conducted. The results of the investigation suggest that secondary oxygen exchange-reaction occurs which not only depends on but also utilises the intermediates in the primary reaction during diperoxovanadate-dependent oxidation of VOSO₄. In an interesting reactiontris(acetylacetonato)-manganese(III), Mn(acac)₃, on being reacted with a hydrogen peroxide adduct, KF·H₂O₂, and bpy and phen afforded crystalline [Mn(acac)₂(bpy)] and [Mn(acac)₂(phen)], respectively. The X-ray structural analysis of [Mn(acac)₂(phen)] showed that the compound crystallised in orthorhombic space groupPbcn. The structure consists of a pseudooctahedral Mn(II) ion being bound to two acac⁻(C₅H₅O ₂ ⁻ ) and a phen ligand with the molecule lying on two-fold axis. Reactivity profiles of two new chromium(VI) reagents viz., pyridinium fluorochromate, C₅H₅NH[CrO₃F] (PFC), and quinolinium fluorochromate C₉H₇NH [CrO₃F] (QFC), have been presented. The compounds are capable of acting as both electron-transfer and oxygen-atom-transfer agents. The X-ray analysis of PFC crystals reveals that the compound crystallises in the orthorhombic space group CmcZ₁. The structure consists of discrete pyridinium cations and CrO₃ F anions with no significant hydrogen bonding. This results in total disorder of the pyridinium cation. The tetrahedral [CrO₃ F]⁻ ion lies on a crystallographic mirror plane.     

Synthesis and characterization of Fe2O3/SiO2 nanocomposites

Fe₂O₃/SiO₂ nanocomposites based on fumed silica A-300 (S_BET = 337 m²/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)₃) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)₃ then oxidized in air at 400–900 °C. Samples with Fe(acac)₃ adsorbed onto nanosilica and samples with Fe₂O₃/SiO₂ including 6–17 wt% of Fe₂O₃ were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe₂O₃ deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)₃ solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)₃ solution in carbon tetrachloride only α-Fe₂O₃ phase is formed in addition to amorphous Fe₂O₃. The Fe₂O₃/SiO₂ materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm³ and S_BET = 265–310 m²/g.     

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes: efficient catalytic activity for crosslinking reaction in ethylene‐vinyl acetate copolymer/alkoxysilane composites

The catalytic performances of several bis(acetylacetonato)metal complexes [Cu(acac)₂, Zn(acac)₂, TiO(acac)₂, VO(acac)₂, MoO₂(acac)₂, and WO₂(acac)₂] were investigated for the crosslinking reaction via transesterifications in the ethylene‐vinyl acetate copolymer/tetraethoxysilane (EVA/TEOS) composite system by means of dynamic attenuated total reflectance Fourier transform infrared, solvent swelling, and solid‐state ²⁹Si cross polarization/magic angle spinning nuclear magnetic resonance techniques. Results of the kinetic examination revealed that MoO₂(acac)₂ and WO₂(acac)₂ exhibited a higher catalytic activity than di‐n‐butyltin(IV) oxide, which is a catalyst most commonly used for the transesterification process in polymer system, but has a toxic effect on the environmental health. And furthermore, the crosslink density and final siloxane network structure of crosslinked EVA/TEOS composites are found to be greatly correlated with the catalyst used. On the basis of the S_N2‐Si pathway, a plausible catalytic mechanism of MoO₂(acac)₂ and WO₂(acac)₂ was proposed for the crosslinking reaction via transesterifications of the vinyl acetate moieties in EVA backbone with the ethoxysilane groups in one TEOS molecule. The findings in this study may fill the blank in the high performance and environmentally friendly catalyst in the field of the crosslinking reactions in polymer system and provide useful clue for other transesterifications. Copyright © 2015 John Wiley & Sons, Ltd.     

具备高首周库仑效率的高性能锂离子电池负极材料Li2Ni2(MoO4)3@C的制备

采用常规的固相反应法结合机械球磨制备了含碳质量分数23.7%的Li₂Ni₂（MoO₄）₃@C复合材料,并应用于锂离子电池负极。与纯Li₂Ni₂（MoO₄）₃相比,Li₂Ni₂（MoO₄）₃@C具有优异的电化学性能,在电流密度为200 mA·g^-1时,50周循环后,可逆容量高达845 mAh·g^-1。值得注意的是,Li₂Ni₂（MoO₄）₃@C的首周库仑效率高达85%。此外,运用循环伏安法对Li₂Ni₂（MoO₄）₃@C复合物存储锂行为进行了初步探索。     

Cr2(WO4)3和Cr2(MoO4)3的负热膨胀特性研究

用液相反应-前驱物烧结法制备了Cr₂(WO₄)₃和Cr₂(MoO₄)₃粉体。298～1 073 K的原位粉末X射线衍射数据表明Cr₂(WO₄)₃和Cr₂(MoO₄)₃的晶胞体积随温度的升高而增大, 本征线热膨胀系数分别为(1.274±0.003)×10^-6 K^-1和(1.612±0.003)×10^-6 K^-1。用热膨胀仪研究了Cr₂(WO₄)₃和Cr₂(MoO₄)₃在静态空气中298～1 073 K范围内热膨胀行为，即开始表现为正热膨胀，随后在相转变点达到最大值，最后表现为负热膨胀，其负热膨胀系数分别为(-7.033±0.014)×10^-6 K^-1和(-9.282±0.019)×10^-6 K^-1。     

Mechanism of Formation of Nanocrystalline ZnO Particles through the Reaction of [Zn(acac)2] with NaOH in EtOH

The mechanism of formation of nanocrystalline ZnO particles from the reaction of zinc acetylacetonate ([Zn(acac)₂]) with 2-equivalent NaOH in boiling EtOH was investigated by characterizing the particles and following the transformation of acac moieties. The reaction was found to proceed via hydrolysis of zinc ethoxide derivatives, followed by dehydration–condensation reactions. High-resolution solid-state CP-MAS¹³C NMR measurements indicate that the ZnO particles are produced through Zn (acac)(OZn)_n(acac) (3). Furthermore, it was suggested that acac⁻ligands play an important role in the generation of nanocrystalline ZnO particles by suppressing the hydrolysis–condensation of Zn(acac)(OZn)_n(acac).     

High Temperature Reactions in the MoO3-Ag2O System

High-temperature reactions were investigated in the MoO₃-Ag₂O system by means of X-ray, DTA and scanning microscopy methods, and a model was proposed according to which first an Ag₂Mo₄O₁₃ phase was formed at the MoO₃ and Ag₂O (or metallic Ag) interface. Subsequently, at the Ag₂Mo₄O₁₃-Ag₂O contact area a layer of Ag₂Mo₂O₇ appeared. If the amount of silver oxide is sufficiently high, a layer of Ag₂MoO₄ is formed between the Ag₂O and Ag₂Mo₂O₇ phases. This revised version was published online in July 2006 with corrections to the Cover Date.     

表面Cu2O纳米颗粒修饰高效促进γ-Bi2MoO6的可见光催化活性

采用水热法在γ-Bi₂MoO₆光催化剂表面修饰了纳米级Cu₂O, 得到了具有高效可见光响应的复合光催化材料, 并利用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、选区电子衍射(SAED)、X射线光电子能谱(XPS)和紫外-可见漫反射光谱(UV-Vis-DRS)等技术对其相结构、微观形貌和光吸收性能进行了表征. 在可见光条件下(λ>400 nm)考察了Cu₂O表面修饰对γ-Bi₂MoO₆光催化降解亚甲基蓝(MB)性能的促进作用. 结果表明, 纳米级Cu₂O(~10 nm)颗粒均匀地修饰于γ-Bi₂MoO₆的表面, 使γ-Bi₂MoO₆的可见光吸收带发生明显红移, 且吸收强度大幅提高, 增强了复合材料光生电子-空穴对的分离效率, 从而使复合材料表现出较高的光催化活性. 当Cu₂O的表面修饰量为1.5%(w)时, 复合光催化剂降解MB的活性与纯γ-Bi₂MoO₆相比提高了6.4倍.     

Polymerizations of chloral,styrene oxide,and methyl methacrylate initiated by the binary system of bis(acetylacetonato)metal(II) and chloral

The binary system of bis(acetylacetonato)metal(II) [M(acac)₂] and chloral induced the polymerization of chloral [M = Mn(II), Co(II), Mg(II), and Cu(II)], the ring-opening polymerization of styrene oxide [M = Co(II) and Mg(II)], and the radical polymerization of methyl methacrylate [M = Mn(II) and Co(II)]. The similar order of activity of M(acac)₂ as the catalyst for the polymerization of chloral and for the aldol reaction of chloral with acetylacetone, the deactivation of the catalyst by the introduction of a substituent at the 3-position of M(acac)₂, the presence of saturated β-diketone at the end of the polymer of chloral and that of styrene oxide, and the visible light spectral data supporting the formation of the β-ketoalcoholate intermediate in the binary system of Co(acac)₂ and chloral are all experimental findings which suggest that M(acac)₂ is subject to the aldol addition by chloral at the 3-position of the chelated acetylacetone and that the resultant β-ketoalcoholate is a common active species for these polymerizations.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. 58. Zur Kenntnis von 2-(Dimethylaminomethyl)ferrocenyl-Verbindungen des Vanadiums,Molybdäns,Wolframs, Thoriums und Urans

Contributions to the Chemistry of Transition Metal Alkyl Compounds. 58 On 2-(Dimethylaminomethyl)ferrocenyl Compounds of Vanadium, Molybdenum, Tungsten, Thorium, and Uranium Earlier results according to which dimethylaminomethylferrocenyl groups (FcN) are able to form stable organometallic chelate compounds were confirmed by synthesis of the heterobimetallic chelate compounds (FcN)₂VO · Li(acac) II , (FcN)MoO₂(acac) III , (FcN)WOCl₃ IV , (FcN)Th(acac)₃ V , and (FcN)UO₂(acac) VI from the corresponding metal acetylacetonates or oxidchlorides and (FcN)Li I . The new compounds were characterized by elemental analysis, the i.r., ¹H-n.m.r., and electron spectra and by their effective magnetic moments.     

Syntheses and characterization of two oxoborates, (Pb3O)2(BO3)2MO4 (M=Cr, Mo)

Two oxoborates, (Pb₃O)₂(BO₃)₂MO₄ (M=Cr, Mo), have been prepared by solid-state reactions below 700 °C. Single-crystal XRD analyses showed that the Cr compound crystallizes in the orthorhombic group Pnma with a=6.4160(13) Å, b=11.635(2) Å, c=18.164(4) Å, Z=4 and the Mo analog in the group Cmcm with a=18.446(4) Å, b=6.3557(13) Å, c=11.657(2) Å, Z=4. Both compounds are characterized by one-dimensional chains formed by corner-sharing OPb₄ tetrahedra. BO₃ and CrO₄ (MoO₄) groups are located around the chains to hold them together via Pb–O bonds. The IR spectra further confirmed the presence of BO₃ groups in both structures and UV–vis diffuse reflectance spectra showed band gaps of about 1.8 and 2.9 eV for the Cr and Mo compounds, respectively. Band structure calculations indicated that (Pb₃O)₂(BO₃)₂MoO₄ is a direct semiconductor with the calculated energy gap of about 2.4 eV.     

Ag/Ag2MoO4/Bi2MoO6复合光催化剂的制备及其光催化性能

采用水热、化学沉积和原位光还原的方法成功制备了新型Ag/Ag₂MoO₄/Bi₂MoO₆三元复合光催化剂。通过X射线粉末衍射（XRD）、扫描电子显微镜（SEM）、X射线光电子能谱（XPS）和紫外可见漫反射光谱（UV-Vis DRS）等技术对材料的组成、形貌、光吸收特性和光电化学性能等进行系统分析。以四环素为目标污染物,研究Ag/Ag₂MoO₄/Bi₂MoO₆在可见光下的光催化性能。研究结果表明,相比于纯Ag₂MoO₄和Bi₂MoO₆,Ag的表面等离子体共振（SPR）效应显著拓宽了催化体系对可见光的吸收能力及响应范围。当Ag₂MoO₄理论负载量（质量分数）为24.6%时,Ag/Ag₂MoO₄/Bi₂MoO₆复合材料在20 min内可将四环素完全降解,且5次循环使用后仍保持较高的催化活性,表现出良好的循环稳定性。     

Reductive carbonylation of aryl and heteroaryl iodides using Pd(acac)2/dppm as an efficient catalyst

Palladium catalyzed simple and efficient protocol for reductive carbonylation of aryl and heteroaryl compounds has been developed. The formylation of aryl and heteroaryl iodides takes place in the presence of Pd(acac)₂/dppm catalyst at 10 bar pressure of synthetic gas to give the desired aromatic and heteroaromatic aldehydes in good to excellent yields. Easy work-up, stability of the catalyst, low catalyst loading and less reaction time are the advantages of this method.     

Dinuclear oxomolybdenum(VI) acetylacetonates: Crystal and molecular structure of Mo2O5(acac)2L2 (L = D2O,DMF)

The behavior of MoO₂(acac)₂ (acac = acetylacetonate) towards representative amines, amides, sulfoxides and phosphine oxides in common solvents has been examined. Compounds of the composition Mo₂O₅(acac)₂L₂ [L = H₂O, D₂O, dimethylformamide (DMF), dimethylacetamide (DMA), dimethylbenzamide (DMBA), tetramethylurea (TMU), dimethylsulfoxide (DMSO), dibutylsulfoxide (Bu₂SO), p-tolylsulfoxide (p-Tol₂SO), tributylphosphine oxide (OPBu₃), triphenylphosphine oxide (OPPh₃), hexamethylphosphoramide (HMPA)], derived from partial hydrolysis of MoO₂(acac)₂ followed by condensation and coordination of L, can readily be isolated. The crystal and molecular structures of Mo₂O₅(acac)₂L₂ (L = D₂O, DMF) have been established by X-ray diffraction analysis.     

Ag/Ag2MoO4/Bi2MoO6复合光催化剂的制备及其光催化性能

采用水热、化学沉积和原位光还原的方法成功制备了新型Ag/Ag₂MoO₄/Bi₂MoO₆三元复合光催化剂。通过X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和紫外可见漫反射光谱(UV-Vis DRS)等技术对材料的组成、形貌、光吸收特性和光电化学性能等进行系统分析。以四环素为目标污染物,研究Ag/Ag₂MoO₄/Bi₂MoO₆在可见光下的光催化性能。研究结果表明,相比于纯Ag₂MoO₄和Bi₂MoO₆,Ag的表面等离子体共振(SPR)效应显著拓宽了催化体系对可见光的吸收能力及响应范围。当Ag₂MoO₄理论负载量(质量分数)为24.6%时,Ag/Ag₂MoO₄/Bi₂MoO₆复合材料在20 min内可将四环素完全降解,且5次循环使用后仍保持较高的催化活性,表现出良好的循环稳定性。     

Complex compounds of tetracycline with WO 4 2− and MoO 4 2− ions. Investigation by pH-metric and conductometric methods

By using pH-metric and conductometric methods it has been found that tetracycline (H₃TC) forms with WO ₄ ^2– and MoO ₄ ^2– ions the following complex compounds: [WO₃HTC]^2–, [WO₃(H₂TC)₂]^2– and [MoO₃(H₂TC)₂]^2–. Stability constants log/gb ₁ ^k =7.86 and log ₁ ^k =7.80 for [WO₃HTC]^2– and [MoO₃HTC]^2–, respectively, have been calculated from pH-metric measurements.     

Ring opening of epoxides with alcohols using Fe(Cp)2BF4 as catalyst

Fe(Cp)₂BF₄ is an efficient catalyst for the alcoholysis of aromatic, aliphatic, and cyclic epoxides giving excellent yields of the corresponding β-alkoxy alcohols under ambient conditions. The methanolysis of styrene oxide using Fe(Cp)₂BF₄ as a catalyst (5 mol %) gave excellent yield of 2-methoxy-2-phenylethanol with complete regio-selectivity. The ring opening of cyclic epoxides gave 77–97% yields of trans-β-methoxy alcohols, in 0.5–6 h. The use of 1,2-epoxyhexane and 1,2-epoxydodecane as substrates gave both regioisomers in excellent yields. The first order rate of reaction with respect to catalyst was observed for the kinetics of ring opening of 1,2-epoxyhexane with methanol.     

Facile one-pot synthesis of 2-arylbenzothiazoles catalyzed by H3PO4/TiO2-ZrO2 (1/1) under solvent-free conditions

A highly efficient and simple protocol for the preparation of 2-arylbenzothiazoles through condensation of 2-aminothiophenol and different aldehydes in the presence of H₃PO₄/TiO₂-ZrO₂(1/1)-cetyl pyridinium bromide (CPB) is described. The reaction proceeded under mild and solvent-free conditions to afford 2-arylbenzothiazole derivatives. In this method, the title compounds were obtained in good to excellent yields and short reaction times. The structures of synthesized products were identified by infrared, ¹H NMR, ¹³C NMR, and mass spectroscopy.     

A comparative study on the dispersion behaviors and surface acid properties of molybdena on CeO2 and ZrO2 (Tet)

Dispersion of molybdena on CeO₂, ZrO₂ (Tet), and a mixture of CeO₂ and ZrO₂ (Tet), was investigated by using laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and temperature programmed reduction (TPR). The results indicate that molybdena is dispersed on both individual oxide support and mixed oxide support at the adopted molybdena loadings (0.2 and 0.8 mmol Mo⁶⁺/100 m²) and the structure of the supported molybdena species is intimate association with its loading amount. Two molybdena species are identified by Raman results, i.e. isolated MoO²⁻₄ species at 0.2 mmol Mo⁶⁺/100 m² and polymolybdate species at 0.8 mmol Mo⁶⁺/100 m². IR spectra of ammonia adsorption prove that isolated MoO²⁻₄ species are Lewis acid sites on the Mo/Ce and/or Zr samples, and the polymolybdate species are Brönsted acid sites on the Mo/Ce and/or Zr samples. Moreover, a combination of the Raman, IR and TPR results confirms that at 0.2 mmol Mo⁶⁺/100 m² Ce + Zr, molybdena is preferentially dispersed on the surface of CeO₂ when a mixed oxide support (CeO₂ and ZrO₂) is present, which was explained in term of the difference of the surface basicity between CeO₂ and ZrO₂ (Tet). Surface structures of the oxide supports were also taken into consideration.