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.     

One-Pot Synthesis of 2,4,5-Trisubstituted Imidazoles Using MoO3/SiO2, an Efficient and Recyclable Catalyst

A simple one-pot synthesis has been developed for the synthesis of 2,4,5-trisubstituted imidazoles using an efficient and recyclable MoO₃/SiO₂ solid acid catalyst by condensation of benzil or benzoin, benzaldehyde, and ammonium acetate in acetonitrile as a solvent. Using this solid catalyst, the reactions could be carried out under mild reaction conditions with very good yield of imidazoles, up to 95%. This catalyst could be recycled very easily, which makes this methodology environmentally benign.     

One-Step Calcination to Gain Exfoliated g-C3N4/MoO2 Composites for High-Performance Photocatalytic Hydrogen Evolution

The difficulty of exposing active sites and easy recombination of photogenerated carriers have always been two critical problems restricting the photocatalytic activity of g-C₃N₄. Herein, a simple (NH₄)₂MoO₄-induced one-step calcination method was successfully introduced to transform bulk g-C₃N₄ into g-C₃N₄/MoO₂ composites with a large specific surface area. During the calcination, with the assistance of NH₃ and water vapor produced by ammonium molybdate, the pyrolytical oxidation and depolymerization of a g-C₃N₄ interlayer were accelerated, finally realizing the exfoliation of the g-C₃N₄. Furthermore, another pyrolytical product of ammonium molybdate was transformed into MoO₂ under an NH₃ atmosphere, which was in situ loaded on the surface of a g-C₃N₄ nanosheet. Additionally, the results of photocatalytic hydrogen evolution under visible light show that the optimal g-C₃N₄/MoO₂ composite has a high specific surface area and much improved performance, which is 4.1 times that of pure bulk g-C₃N₄. Such performance improvement can be attributed to the full exposure of active sites and the formation of abundant heterojunctions. However, with an increasing feed amount of ammonium molybdate, the oxidation degree of g-C₃N₄ was enhanced, which would widen the band gap of g-C₃N₄, leading to a weaker response ability to visible light. The present strategy will provide a new idea for the simple realization of exfoliation and constructing a heterojunction for g-C₃N₄ simultaneously.     

Enriched Surface Oxygen Vacancies of Fe2(MoO4)3 Catalysts for a PDS-Activated photoFenton System

The environmentally benign Fe₂(MoO₄)₃ plays a crucial role in the transformation of organic contaminants, either through catalytically decomposing oxidants or through directly oxidizing the target pollutants. Because of their dual roles and the complex surface chemical reactions, the mechanism involved in Fe₂(MoO₄)₃-catalyzed PDS activation processes remains obscure. In this study, Fe₂(MoO₄)₃ was prepared via the hydrothermal and calcine method, and photoFenton degradation of methyl orange (MO) was used to evaluate the catalytic performance of Fe₂(MoO₄)₃. Fe₂(MoO₄)₃ catalysts with abundant surface oxygen vacancies were used to construct a synergistic system involving a photocatalyst and PDS activation. The oxygen vacancies and Fe²⁺/Fe³⁺ shuttle played key roles in the novel pathways for generation of •O₂⁻, h⁺, and ¹O₂ in the UV–Vis + PDS + FMO-6 photoFenton system. This study advances the fundamental understanding of the underlying mechanism involved in the transition metal oxide-catalyzed PDS activation processes.     

三维花状Fe_2(MoO_4)_3微米球的水热制备及电化学性能

以Fe Cl3·7H2O和Na2Mo O4为原料,采用水热合成法制备三维花状Fe2(Mo O4)3微米球。探讨不同合成温度对样品形貌的影响,利用XRD、SEM和EDS等分析技术对样品的结构、形貌进行了表征,对该材料的电化学性能进行了测试。结果表明:Fe2(Mo O4)3微米球是由二维纳米片自组装而成的花状结构,合成温度为160℃时,制备的样品具有良好的电化学性能,当电流密度为100 m A·g-1,首次放电比容量为1 431 m Ah·g-1;并具有较好的循环性能和倍率性能。并对160℃合成样品表现较好电化学性能的原因进行了探讨。     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

高活性耐硫MoO3改性NiO-Al2O3催化剂用于焦炉煤气甲烷化

采用双水解共沉淀法结合浸渍法合成了系列的MoO₃改性的xMoO₃/NiO-Al₂O₃催化剂(x%为MoO₃的质量分数),利用固定床装置对催化剂的甲烷化反应活性和耐硫性能进行评价,并对失活前后催化剂进行详细表征。结果表明,随着MoO₃含量的升高MoO₃改性后的催化剂甲烷化活性有所下降,但MoO₃的掺杂显著提升了催化剂的耐硫性能。催化剂低温甲烷化活性降低的原因在于MoO₃负载量的增加降低了催化剂的活性比表面积,但MoO₃的引入也为硫化物提供了一个竞争吸附位点,进而延缓了活性位点的硫中毒过程。当 MoO₃负载量(质量分数)为 12.5% 时,12.5MoO₃/NiO-Al₂O₃催化剂在 143 mg·m^-3 H₂S/H₂气氛下运行时间长达7 h,远高于其他催化剂。12.5MoO₃/NiO-Al₂O₃催化剂吸收硫的量(质量分数)达到0.71%,是NiO-Al₂O₃催化剂硫吸附量的1.48倍。XPS表征进一步发现12.5MoO₃/NiO-Al₂O₃催化剂表面生成的MoS₂最多,这说明在此负载量下Mo优先吸附了更多的硫而保护了活性位点。此外,MoO₃负载量为12.5%时,MoO₃在催化剂表面接近单层分散阀值,当竞争吸附发生时,为硫化物提供更多的吸附位点。     

高活性耐硫MoO3改性NiO-Al2O3催化剂用于焦炉煤气甲烷化

采用双水解共沉淀法结合浸渍法合成了系列的MoO₃改性的xMoO₃/NiO-Al₂O₃催化剂(x%为MoO₃的质量分数),利用固定床装置对催化剂的甲烷化反应活性和耐硫性能进行评价,并对失活前后催化剂进行详细表征。结果表明,随着MoO₃含量的升高MoO₃改性后的催化剂甲烷化活性有所下降,但MoO₃的掺杂显著提升了催化剂的耐硫性能。催化剂低温甲烷化活性降低的原因在于MoO₃负载量的增加降低了催化剂的活性比表面积,但MoO₃的引入也为硫化物提供了一个竞争吸附位点,进而延缓了活性位点的硫中毒过程。当MoO₃负载量(质量分数)为12.5%时,12.5MoO₃/NiO-Al₂O₃催化剂在143 mg·m^-3 H₂S/H₂气氛下运行时间长达7 h,远高于其他催化剂。12.5MoO₃/NiO-Al₂O₃催化剂吸收硫的量(质量分数)达到0.71%,是NiO-Al₂O₃催化剂硫吸附量的1.48倍。XPS表征进一步发现12.5MoO₃/NiO-Al₂O₃催化剂表面生成的MoS₂最多,这说明在此负载量下Mo优先吸附了更多的硫而保护了活性位点。此外,MoO₃负载量为12.5%时,MoO₃在催化剂表面接近单层分散阀值,当竞争吸附发生时,为硫化物提供更多的吸附位点。     

Influence of ZrO2 on Carbon Monoxide Oxidation Over Pd/Al2O3

The influence of ZrO₂ on the properties of Al₂O₃ and performances of Pd/Al₂O₃ catalyst in CO oxidation have been investigated. TPD results show that the activity enhanced is due to the increase of the adsorptive capacity of CO and the activation of C=O bond after the introduction of ZrO₂.     

Regioselective Ring Opening of Styrene Oxide Catalyzed by MoO2(acac)2

The ring-opening reaction of styrene oxide with various nitrogen, oxygen, and carbon nucleophiles catalyzed by MoO₂(acac)₂ was described. The corresponding ring-opening compounds with nearly 100% regioselectivities were obtained under mild conditions in moderate to good yields. MoO₂(acac)₂ is a highly efficient catalyst for the ring opening of styrene oxide. The reaction serves as a simple and efficient method for the synthesis of 1,2-bifunctional compounds.     

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。     

Ethoxy Groups on ZrO2, CuO,and CuO/ZrO2 Studied by IR Spectroscopy

The formation, properties, decomposition and reactions of ethoxy groups on ZrO₂, CuO, and CuO/ZrO₂ were followed by IR spectroscopy. The reaction of ethanol with terminal Zr-OH groups leads to the formation of monodendate ethoxy groups (type I), whereas the reaction of ethanol with tribridged Zr-OH grups results in the formation of bidendate ethoxyls (type II). In both cases, water is produced. Ethoxy groups of type II were also formed on CuO. The type of the surface species detected after interaction of ethanol with CuO/ZrO₂ was the same as detected for both oxides (i.e., ZrO₂ and CuO) separately. This suggests that no new phase was formed in the mixed oxide system. At higher temperatures, ethoxy groups were oxidized forming acetate ions. Gaseous ethanol present in the cell was oxidized to acetaldehyde without the intermediacy of ethoxy groups.     

Structural and electrical properties of the 2Bi2O3·3ZrO2 system

Powder mixtures of α-Bi₂O₃ (bismite) and monoclinic m-ZrO₂ (baddeleyite) in the molar ratio 2:3 were mechanochemically and thermally treated with the goal to examine the phases, which may appear during such procedures. The prepared samples were characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), electrical measurements, as well as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanochemical reaction leads to the gradual formation of a nanocrystalline phase, which resembles δ-Bi₂O₃, a high-temperature Bi₂O₃ polymorph. Isothermal sintering in air at a temperature of 820 °C for 24 h followed by quenching to room temperature yielded a mixture of ZrO₂-stabilized β-Bi₂O₃ and m-ZrO₂ phases, whereas in slowly cooled products, the complete separation of the initial α-Bi₂O₃ and m-ZrO₂ constituents was observed. The dielectric permittivity of the sintered samples significantly depended on the temperature. The sintered and quenched samples exhibited a hysteresis dependence of the dielectric shift, showing that the ZrO₂-doped β-Bi₂O₃ phase possess ferroelectric properties, which were detected for the first time. This fact, together with Rietveld refinement of the β-Bi₂O₃/m-ZrO₂ mixture based on neutron powder diffraction data showed that ZrO₂-doped β-Bi₂O₃ has a non-centrosymmetric structure with as the true space group. The ZrO₂ content in the doped β-Bi₂O₃ and the crystal chemical reasons for the stabilization of the β-Bi₂O₃ phase by the addition of m-ZrO₂ are discussed.     

CaO/ZrO2固体碱催化水解CFC-12的研究

采用沉淀过饱和浸渍法制备CaO/ZrO₂固体碱催化剂,通过XRD、SEM、EDS、N₂吸附-脱附、FT-IR和CO₂-TPD表征手段对催化剂进行表征,同时研究了催化剂焙烧温度、催化水解温度、水蒸气浓度与总流量对CFC-12转化率的影响.结果表明,在焙烧温度为500℃、催化水解温度为400℃、水蒸气浓度为25%、总流量为5 mL/min时CFC-12的转化率最高,达到95.80%,主要产物为HCl、HF和CO₂,副产物为CFC-13.表征结果表明其为典型的介孔材料,并且纯度较高,经过焙烧后CaO和ZrO₂形成了固溶体,500℃焙烧的催化剂具有较高的比表面积和孔容,焙烧温度过高催化剂会烧结成块,孔结构遭到破坏.CO₂-TPD表征结果表明催化剂的活性中心为碱,并且高的焙烧温度会降低其碱性.     

Phase equilibria up to the solidus line in the V2O5−Cr2(MoO4)3 system

Phase equilibria being established in the subsolidus area of the V₂O₅?Cr₂(MoO₄)₃ system at the whole component concentration range have been studied basing on DTA and X-ray phase powder diffraction. It has been established that the system is not a real two-component system in the subsolidus area. The fact has been proved by the presence of fields in that area, where three solid phases remain in mutual equilibrium.     

Effects of the preparation methods on the properties of Ni-La2O3-SiO2 catalysts for m -dinitrobenzene hydrogenation

Ni-La₂O₃-SiO₂ catalysts were prepared by wetness impregnation and sol-gel method followed by conventional drying and supercritical drying, respectively. Their physico-chemical properties and activity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine were investigated by BET, XRD, TPR, H₂-TPD and activity tests. The results showed that the structural and catalytic properties of the Ni-La₂O₃-SiO₂ catalysts obviously depended on the preparation method and the drying mode. The catalyst prepared by the sol-gel method in combination with conventional drying exhibited the highest catalytic activity among the catalysts tested, attributable to its well-dispersed nickel particles and larger active nickel surface area.     

SO42-改性后的TiO2(锐钛和/或金红石)表面上MoO3的分散性质研究

采用红外(IR)、拉曼(Raman)、X-射线衍射(XRD)、程序升温还原(TPR)等方法考察了经硫酸根改性后的金红石(SR)与锐钛矿(SA)的混合比例变化时的负载型催化剂，MoO₃ / TiO₂(SR+SA)，的一些物理化学性质(如活性组分MoO₃的分散行为、表面酸碱性、氧化还原性)的变化规律。结果表明：对于MoO₃ / TiO₂(SR+SA)样品，低含量MoO₃表面分散时倾向于优先与混合载体中的改性金红石(SR)发生作用；TiO₂载体表面SO₄^2-的存在，使得载体表面产生了新的酸性位，导致样品中表面分散的钼物种主要以聚合八面体状态存在。     

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.     

La(OH)3和 La2O2CO3纳 米 棒 的 合 成 及 其 催 化 Claisen-Schmidt缩合反应性能简

通过调节溶液的pH值,在水热条件下合成出长径比为2-45的La（OH）₃纳米棒. 对水热合成过程中间体的结构演变分析,发现高碱度有利于小尺寸晶核的形成,La（OH）₃晶体结构的各向异性导致这些晶种沿着C轴方向生长,进而形成纳米棒结构. 将La（OH）₃纳米棒前驱体于773 K焙烧可以得到长径比为2-20的La₂O₂CO₃纳米棒. 随着长径比的增加,La₂O₂CO₃纳米棒暴露的（110）晶面逐渐增加,La³⁺-O^2-碱性位的数目也从0.08增加到0.24 mmol/g. 因此,在Claisen-Schmidt缩合反应中,La₂O₂CO₃纳米棒催化剂上的反应速率随着长径比的增加而逐渐增大.     

Monolith Manganese-Based Catalyst Supported on ZrO2-TiO2 for NH3-SCR Reaction at Low Temperature

Monolith catalysts were prepared using TiO₂ and ZrO₂-TiO₂ as supports with MnO₂ as active component and Fe₂O₃ as promoter. The catalytic activities at low temperature and stability at high temperature for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) in the presence of excessive O₂ were studied after the catalysts calcined at different temperatures. The catalysts were characterized by X-ray diffraction (XRD), specific surface area measurements (BET), oxygen storage capacity (OSC), and temperature programmed reduction (H₂-TPR). The results indicated that the catalyst supported on ZrO₂-TiO₂ had excellent stability at high temperature, and possessed high specific surface area and oxygen storage capacity, and had strong redox property. The results of the catalytic activities indicated that the monolith manganese-based catalyst using ZrO₂-TiO₂ as support had evidently improved the activity of NH₃-SCR reduction reaction at low temperature, and it showed great potential for practical application.