改性钛锆复合氧化物催化环己酮肟气相Beckmann重 排反应

制备了经SO4^2-,PO4^3-,MoO3,WO3和B2O3改性的钛锆复合氧化物(TiO2-ZrO2)催化剂,并用常压连续流动固定床微型反应器考察了它们对环己酮肟气相Beckmann重排反应制己内酰胺的催化性能。结果表明,在反应温度300℃时,B2O3/TiO2-ZrO2具有较高的己内酰胺选择性(97.0%)和收率(96.7%),且明显高于B2O3/TiO2和B2O3/ZrO2催化剂,用N2吸附和NH3-TPD,CO2-TPD等方法对催化剂的经表面积、孔容、孔分布和表面酸、碱性分别进行了测定,讨论了这些物化性能对催化剂活性、选择性和稳定性的影响。     

B2O3/TiO2-ZrO2催化环己酮肟气相Beckmann重排反应研究 Ⅰ.B2O3含量的影响

 制备了不同B2O3含量（0～20％）的B2O3／TiO2－ZrO2固体酸催\r\n化剂，用XRD，FT－IR，N2吸附及NH3－TPD等方法测定了其结构、比表\r\n面积、孔分布和表面酸性．结果表明，当B2O3含量较低（≤5％）时，\r\n催化剂呈无定形态，样品中的B2O3主要以BO4结构存在．当B2O3含量较\r\n高（≥8％）时，催化剂中的TiO2－ZrO2以ZrTiO4晶相存在，分散于Ti\r\nO2－ZrO2表面的B2O3主要以玻璃体形式和BO3结构存在．随着B2O3含量\r\n的增加，催化剂的比表面积减小，孔径增大．300℃下的环己酮肟气相\r\nBeck－mann重排反应结果表明，随着B2O3含量的增加，己内酰胺的选择\r\n性逐渐增大，而己内酰胺的收率在B2O3含量为12％时达到最大值．讨论\r\n了B2O3／TiO2－ZrO2的催化性能与其表面酸性及孔径大小的关系．     

环己酮肟在改性氧化锆催化剂上的Beckmann重排反应Ⅴ.活化焙烧温度对B2O3/ZrO2催化剂的影响

 采用BET，XRD，TG－DTA，FT－IR，XPS和NH3－TPD等分析手段，研究了活化焙烧温度（500～800℃）对B2O3／ZrO2催化剂织构／结构、表面性质和环己酮肟气相重排反应的影响．催化剂活化焙烧温度升高促进了ZrO2向单斜晶相转化，同时活性组分氧化硼由以BO4为主要结构单元的物种转变为以BO3为基本结构单元的B2O3，导致催化剂比表面积、孔体积以及表面酸量减小，ZrO2与B2O3之间的相互作用减弱．700℃活化焙烧的催化剂表面拥有最大比例的中强酸中心，而且Beckmann反应的活性稳定性最高．这些结果表明，活化焙烧温度对B2O3／ZrO2催化剂上气相重排反应的影响主要是通过改变催化剂中B原子的配位状态和表面酸性实现的．     

环已酮肟在B2O3／Al2O3—TiO2催化剂上的气相Beckemann重排反应

制备了B2O3/Al2O3-TiO2复合载体催化剂,并考察了其对环已酮肟气相Beckemann重排制已内酰胺反应的催化性能。结果表明,载体中TiO2的含量、B2O3的负载量、载体的预处理温度及催化剂的焙烧温度等均对催化剂的性能产生明显的影响。当载体中TiO2含量为60%,B2O3负载量为20%,催化剂经350℃焙烧时,环已酮肟的气相Beckemann重排反应的转化率和选择性很高。用BET,NH3-TPD,XRD和IR等方法对催化剂的织构、表面酸性和晶相等进行了表征,并与催化剂和活性进行了关联,表明催化剂表面中等强度的酸中心浓度与催化剂的选择性具有对应关系。     

B2O3/ZrO2催化剂的11B MAS NMR表征

 用11B MAS NMR技术研究了B2O3/ZrO2催化剂中B2O3活性组分的存在形式及作用状态. 结果表明,B2O3在ZrO2表面以三配位BO3与四配位BO4结构单元存在. ZrO2载体的预焙烧温度和硼含量对B2O3的作用状态具有重要的影响,并改变BO3与BO4结构单元之间的比例. 催化剂表面吸附水的存在对BO4与BO3之间的分布有很大的影响,催化剂焙烧脱水至少可使部分BO4转化为BO3. BO4结构形式容易在无定形的微孔大比表面积的ZrO2表面形成; BO3结构形式却倾向于在结晶形的中孔小比表面积的ZrO2上存在.     

B2O3/ZrO2催化剂稳定性和再生性能的研究

以气相环己酮肟重排反应合成己内酰胺是多相催化研究领域的重要课题之一[1,2]. 本研究小组曾首次报道了B2O3/ZrO2催化剂对该反应表现出较高的活性和己内酰胺选择性,但是该催化剂的稳定性和再生性能较差[3,4]. 而通过对催化剂的组成和结构与己内酰胺产率关系的研究表明,当B2O3在ZrO2载体(60 m2/g)表面平均形成约两个单层厚度的B2O3表面相时催化剂性能最好[2],这预示着增加ZrO2载体的比表面积可望改善B2O3/ZrO2催化剂的性能. 采用常规方法制备的ZrO(OH)2经600 ℃焙烧后所得ZrO2的比表面积一般不超过60 m2/g. 本文以蒸煮回流ZrO(OH)2水凝胶的方法制备了高比表面积的ZrO2,并考察了以其为载体的B2O3/ZrO2催化剂对气相环己酮肟重排反应的催化性能.     

环己酮肟在改性氧化锆催化剂上的Beckmann重排反应 V．活化焙烧温度对B2O3／ZrO2催化剂的影响

采用BET，XRD，TG－DTA，FT－IR，XPS和NH3－TPD等分析手段，研究了活化焙烧温度（500－800℃）对B2O3／ZrO2催化剂织构／结构、表面性质和环己酮肟气相重排反应的影响。催化剂活化焙烧温度升高促进了ZrO2向单斜晶相转化，同时活性组分氧化硼由以BO4为主要结构单元的物种转变为以BO3为基本结构单元的B2O3，导致催化剂比表面积，孔体积以及表面酸量减小，ZrO2与B2O3之间的相互作用减弱、700℃活化焙烧的催化剂表面拥有最大比例的中强酸中心，而且Beckmann反应的活性稳定性最高。这些结果表明，活化焙烧温度为B2O3／ZrO2催化剂上气相重排反应的影响主要是通过改变催化剂中B原子的配位状态和表面酸性实现的。     

环己酮肟在B2O3/Al2O3-TiO2催化剂上的气相Beckmann重排反应

制备了B2O3/Al2O3-TiO2复合载体催化剂,并考察了其对环己酮肟气相Beckmann重排制己内酰胺反应的催化性能. 结果表明,载体中TiO2的含量、B2O3的负载量、载体的预处理温度及催化剂的焙烧温度等均对催化剂的性能产生明显的影响. 当载体中TiO2含量为60%,B2O3负载量为20%,催化剂经350 ℃焙烧时,环己酮肟的气相Beckmann重排反应的转化率和选择性很高. 用BET,NH3-TPD,XRD和IR等方法对催化剂的织构、表面酸性和晶相等进行了表征,并与催化剂的活性进行了关联,表明催化剂表面中等强度的酸中心浓度与催化剂的选择性具有对应关系.     

钙硼对CuO/Al_2O_3催化剂结构及醋酸仲丁酯氢解性能的影响

以经氧化钙和氧化硼改性的氧化铝为载体,采用浸渍法制备了负载型CuO/Al2O3催化剂,采用XRD、BET、TPR和NH3-TPD技术对催化剂CuO/Al2O3进行了表征.结果表明,氧化硼既可以作为结构性助剂提高铜在催化剂表面的分散度,又可以作为电子性助剂有利于催化剂表面氧化铜物种的稳定;氧化钙的引入降低了催化剂表面酸性,有利于催化剂的选择性提高.采用氧化硼和氧化钙改性的Cu10B20Ca30为催化剂,醋酸仲丁酯转化率可达99.5%,生成仲丁醇和乙醇的选择性分别达98.9%和97.8%.     

掺杂Nb、B等元素对MoVTe催化剂一步催化氧化丙烯制丙烯酸的影响

采用共沉淀法制备MoVTe复合氧化物系列催化剂,研究其一步氧化丙烯制备丙烯酸的催化性能,并采用XRD、ICP、EDS、H2-TPR、NH3-TPD对催化剂的结构、表面进行表征.结果表明,加入适量的Nb显著提高MoVTe复合氧化物对丙烯酸的选择性,可从34.1%提高至83.5%;同时丙烯酸的收率从24.7%提高到48.8%.适量Nb存在可以稳定催化剂表面Te元素,从而提高了丙烯酸的选择性;B、Fe、Ce、W元素掺杂对催化剂催化性能产生不同的影响,B掺杂提高了催化剂的催化性能,加入酸性元素硼可增加MoVTeNb复合氧化物催化剂表面丙烯活化位点(Te4+=O·Te3+─O·)的数目,使得丙烯转化率和丙烯酸收率显著提高,分别高达89.8%和64.8%.     

Direct formation of thermally stabilized amorphous mesoporous Fe2O3/SiO2 nanocomposites by hydrolysis of aqueous iron III nitrate in sols of spherical silica particles

Nanocomposite materials containing 10% and 20% iron oxide/silica, Fe2O3/SiO2 (w/w), were prepared by direct hydrolysis of aqueous iron III nitrate solution in sols of freshly prepared spherical silica particles (St?ber particles) present in their mother liquors. This was followed by aging, drying, calcination up to 600 degrees C through two different ramp rates, and then isothermal calcinations at 600 degrees C for 3 h. The calcined and the uncalcined (dried at 120 degrees C) composites were characterized by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption techniques, and scanning electron microscopy as required. XRD patterns of the calcined composites showed no line broadening at any d-spacing positions of iron oxide phases, thereby reflecting the amorphous nature of Fe2O3 in the composite. The calcined composites showed nitrogen adsorption isotherms characterizing type IV isotherms with high surface area. Moreover, surface area increased with the increasing of the iron oxide ratio and lowering of the calcination ramp rate. Results indicated that iron oxide particles were dispersed on the exterior of silica particles as isolated and/or aggregated nanoparticles. The formation of the title composite was discussed in terms of the hydrolysis and condensation mechanisms of the inorganic FeIII precursor in the silica sols. Thereby, fast nucleation and limited growth of hydrous iron oxide led to the formation of nanoparticles that spread interactively on the hydroxylated surface of spherical silica particles. Therefore, a nanostructured composite of amorphous nanoparticles of iron oxide (as a shell) spreading on the surface of silica particles (as a core) was formed. This morphology limited the aggregation of Fe2O3 nanoparticles, prevented silica particle coalescence at high temperatures, and enhanced thermal stability.     

Formation and characterization of two FeO3 isomers in solid argon

Two FeO 3 isomers were prepared and characterized using matrix isolation infrared spectroscopy and theoretical calculations. The iron monoxide molecules produced from laser evaporation of the bulk iron oxide target react with dioxygen in solid argon to form the (eta (2)-O 2)FeO complex spontaneously on annealing. The (eta (2)-O 2)FeO complex was predicted to have a (5)B 2 ground state with a planar C 2 v structure, in which the O 2 fragment is side-on bonded to the iron center. The (eta (2)-O 2)FeO complex rearranges to the more stable iron trioxide isomer upon visible light (lambda > 500 nm) irradiation. The iron trioxide molecule was predicted to have a closed-shell singlet ground state with a planar D 3 h symmetry, in which the iron possesses a +6 oxidation state.     

Spontaneous vesicles, disks, threadlike and spherical micelles found in the solubilization of DMPC liposomes by the detergent DTAC

Iron oxide/MCM-41 nanocomposites, Fe(2)O(3)/MCM-41, containing 5%, 10%, and 20% (w/w) iron oxide, were prepared via a direct nonhydrothermal method at room temperature. The preparations were preformed by using iron(III) nitrate, tetra-ethoxysilane (TEOS), and cetyltrimethylammonium bromide (CTAB) mixed or unmixed with dodecyltrimethylammonium bromide (DTAB). The produced materials were dried and calcined at 550 °C for 3 h. Test materials were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), N(2) gas adsorption/desorption isotherms, small angle and wide angle X-ray diffraction (XRD). Results indicate that mixing of CTAB with DTAB does not harm the formation of blank MCM-41 structure. For the composite Fe(2)O(3)/MCM-41 materials, results showed formation of more stable MCM-41 structure with higher surface area and improved porosity in the presence of mixed (CTAB+DTAB) than in the presence of single (CTAB) surfactants for up to 10% Fe(2)O(3)/MCM-41 (w/w). This was explained in terms of the effect DTAB on contraction of the template micellar size to compensate for the expected size expansion upon the addition of ionic iron(III) nitrate precursor. Highly dispersed Fe(2)O(3) nanoparticles were formed in all cases even with the highest iron oxide percentage. Formation of the nanocomposites was postulated to be determined by fast nucleation and slow growth of iron oxide species, which facilitated formation of well dispersed iron oxide nanoparticles inside and on the wall of the MCM-41 material.     

Control of structure and particle size of iron oxide on carrier oxide by the sol-gel method using organic polydentate ligands

It was tried to control the structure and particle size of iron oxide supported on a carrier by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands. The iron oxide/carrier composites were prepared by calcining carrier oxides impregnated with organic ligands and Fe(NO₃)₃·9H₂O. When ligands were diacetone alcohol and ethanol, the structure of the iron oxide was exclusively corundum. But, with ligands such as ethylene glycol, citric acid and galacturonic acid, the structure of the iron oxide changed from corundum to spinel as the amount of ligands used increased. With both series of ring and straight chain saccharides, size of the iron oxide particles changed depending on saccharides used. It was thus concluded that the structure and particle size of iron oxide supported on a carrier can be regulated by using organic polydentate ligands.     

Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process.

The synthesis of highly crystalline and monodisperse gamma-Fe(2)O(3) nanocrystallites is reported. High-temperature (300 degrees C) aging of iron-oleic acid metal complex, which was prepared by the thermal decomposition of iron pentacarbonyl in the presence of oleic acid at 100 degrees C, was found to generate monodisperse iron nanoparticles. The resulting iron nanoparticles were transformed to monodisperse gamma-Fe(2)O(3) nanocrystallites by controlled oxidation by using trimethylamine oxide as a mild oxidant. Particle size can be varied from 4 to 16 nm by controlling the experimental parameters. Transmission electron microscopic images of the particles showed 2-dimensional and 3-dimensional assembly of particles, demonstrating the uniformity of these nanoparticles. Electron diffraction, X-ray diffraction, and high-resolution transmission electron microscopic (TEM) images of the nanoparticles showed the highly crystalline nature of the gamma-Fe(2)O(3) structures. Monodisperse gamma-Fe(2)O(3) nanocrystallites with a particle size of 13 nm also can be generated from the direct oxidation of iron pentacarbonyl in the presence of oleic acid with trimethylamine oxide as an oxidant.     

CO/H_2合成混合醇Cu-Co-Fe催化剂的组成和铁的分散行为(英文)

Cu-Co-Fe catalysts were prepared by coprecipitation of Cu-Co nitrate solutions with Na2CO3 and impregnation of iron nitrate on the Cu-Co precipitates by incipient wetness method; and their phase structure, composition and iron dispersion behavior were studied by XRD, SEM and SAM techniques. The catalyst precursor consists of CuO, Co3O4 and (-Fe2O3. The intensity of XRD peak of Fe2O3 changes as the relative content of iron varies. No X-ray diffraction peak of iron oxide appears unless the content of iron surpasses a threshold value.     

Iron oxide coated gold nanorods: synthesis, characterization, and magnetic manipulation

We report a simple process to generate iron oxide coated gold nanorods. Gold nanorods, synthesized by our three-step seed mediated protocol, were coated with a layer of polymer, poly(sodium 4-styrenesulfonate). The negatively charged polymer on the nanorod surface electrostatically attracted a mixture of aqueous iron(II) and iron(III) ions. Base-mediated coprecipitation of iron salts was used to form uniform coatings of iron oxide nanoparticles onto the surface of gold nanorods. The magnetic properties were studied using a superconducting quantum interference device (SQUID) magnetometer, which indicated superparamagnetic behavior of the composites. These iron oxide coated gold nanorods were studied for macroscopic magnetic manipulation and were found to be weakly magnetic. For comparison, premade iron oxide nanoparticles, attached to gold nanorods by electrostatic interactions, were also studied. Although control over uniform coating of the nanorods was difficult to achieve, magnetic manipulation was improved in the latter case. The products of both synthetic methods were monitored by UV-vis spectroscopy, zeta potential measurements, and transmission electron microscopy. X-ray photoelectron spectroscopy was used to determine the oxidation state of iron in the gold nanorod-iron oxide composites, which is consistent with Fe2O3 rather than Fe3O4. The simple method of iron oxide coating is general and applicable to different nanoparticles, and it enables magnetic field-assisted ordering of assemblies of nanoparticles for different applications.     

Factors affecting the catalytic epoxidation of olefins by iron porphyrin complexes and H2O2 in protic solvents

The catalytic epoxidation of cyclohexene by iron(III) porphyrin complexes and H2O2 has been investigated in alcohol solvents to understand factors affecting the catalyst activity in protic solvents. The yields of cyclohexene oxide and the Fe(III/II) reduction potentials of iron porphyrin complexes were significantly affected by the protic solvents, and there was a close correlation between the product yields and the reduction potentials of the iron porphyrin catalysts. The role of alcohol solvents was proposed to control the electronic nature of iron porphyrin complexes that determines the catalyst activity in the epoxidation of olefins by H2O2. We have also demonstrated that an electron-deficient iron porphyrin complex can catalyze the epoxidation of olefins by H2O2 under conditions of limiting substrate with high conversion efficiency in a solvent mixture of CH3OH and CH2Cl2.     

合成醇催化剂中组分间的相互作用

近年来,CO/H_2催化合成低碳混合醇的研究受到广泛的关注。低碳混合醇可作为掺合汽油的助溶剂、燃料和代油品,一经分离则是非常重要的化工原料,应用价值很大。催化剂是合成过程的关键,七十年代以来该领域研究取得很大进展,如美国Dow公司开发的MoS_2体系,意大利Sham公司研制的“甲基燃料”合成催化剂及法国IFP开发的混合氧化物型“乙基燃料”合成催化剂等,引起人们的极大重视。催化剂的表面     

纳米Fe2O3/膨润土复合催化剂的制备及光催化活性

Using the surfactant（PVA）in the preparation process,the nano-iron oxide / Bentonites were prepared through a reaction between a solution of iron salt and a dispersion of Bentonite clay. The X-ray diffraction（XRD）results reveal that the catalysts mainly consist of α-Fe2O3 . The photo-catalytic activity of iron oxide / Bentonites was examined in the photo-assisted degradation of an organic azo-dye Orange Ⅱ. It is found that the photo-catalytic activity of the catalysts is much higher than that of α-Fe2O3 . The experimental results（using the different catalysts in which the quantities of Fe2O3 are equal）demonstrate that the photo-catalytic activity of catalysts is as follows:Fe-A > Fe-B > Fe-C > Fe-D. In addition,the research shows that Orange Ⅱ degradation ratio of heterogeneous photo-Fenton process is higher than that of homogeneous one.