粘土担载的钼基催化剂的制备、结构及CO加氢合成醇性能

采用溶胶凝胶法与等体积浸渍相结合制备了一系列以粘土为载体的K-Co-Mo催化剂. 采用XRD、N₂等温吸脱附、H_{26+的还原,但对Mo⁴⁺和Co²⁺的还原没有明显的影响. 催化剂经还原后,在其表面生成了一种更低价态的Mo^δ+(1<δ<4)物种,被认为是合成醇的活性中心. 与非负载催化剂相比,粘土担载的K-Co-Mo具有更高的合成醇性能. 负载型催化剂具有较高的活性物种分散度,并且其介孔结构在一定程度上延长了合成醇反应中间体的滞留时间,从而促进了低碳醇的生成. 经773 K还原的催化剂具有较高的活性,其原因可为催化剂表面具有较高含量的Mo^δ+物种.}     

沉淀方法及铈掺杂对铜锰氧化物催化剂催化氧化CO性能的影响

研究了铈掺杂及沉淀方法对铜锰氧化物催化剂的结构特性及室温催化氧化CO性能的影响. 使用X射线衍射、N₂吸附脱附、等离子体发射光谱、程序升温还原、紫外可见漫反射以及X射线光电子能谱等手段对各催化剂进行了表征. 发现掺杂少量的铈于铜锰氧化物催化剂中,CeO₂相高度分散并能阻止催化剂的烧结和团聚,所制得的催化剂的颗粒较小,氧化还原性能提高,比表面增大,并形成了较多的活性位点,使其对CO的催化氧化性能明显提高.     

利用生物质合成气在钼基催化剂上制备混合醇

采用柠檬酸作络合剂的溶胶凝胶法制备了一系列的钼基催化剂,并应用到从生物质气化合成气有效合成低碳混合醇的实际过程中. 在钼基催化剂中,Cu₁Co₁Fe₁Mo₁Zn_0.5-6%K催化剂具有相对较高的混合醇时空产率. 通过实验发现, 反应温度在340 oC以下时,碳转化率随着反应温度的增加而不断上升,总醇的选择性却逐渐下降. 在试验测试的条件内,从生物质气化合成气合成的混合醇最大产率为494.8 g/(kg_catal·h),其中C2⁺醇(C2-C6高碳醇)占总醇含量的80.4%. 在不同的钼基催化剂上合成的混合醇,其醇分布除甲醇以外均符合Schulz-Flory方程. 在醇类产物中,C2以上的高级醇含量占总醇重量的百分比为70%-85%. 同时,利用X射线衍射和BET等表征手段对钼基催化剂的形态和结构进行了表征. 从生物质合成气生产的洁净生物质燃料混合醇具有较高的辛烷值,可以用作运输燃料或汽油的添加剂.     

煅烧温度对Cu/HMOR催化剂结构及其催化二甲醚羰基化反应性能影响

采用离子交换法在不同煅烧温度下制备HMOR负载Cu(Cu/HMOR)催化剂,用于催化二甲醚(DME)羰基化合成乙酸甲酯(MA)反应. 活性测试结果表明430 oC煅烧制得Cu/HMOR具有较好催化活性,在210 oC、1.5 MPa、空速4883 h^-1下DME转化率为97.2%,MA选择性为97.9%. 对催化剂进行X射线衍射、N₂物理吸附、NH₃程序升温脱附、CO程序升温脱附及拉曼方法表征. 催化剂经一定的煅烧温度有利于Cu离子迁移及扩散和硝酸铜完全分解,从而使HMOR载体具有较多的酸性活性位、大比表面、适宜的微孔结构以及更多的CO吸附位.     

草酸铕颗粒微米层状颗粒的合成及其光学性能

在室温条件下, 以柠檬酸钠为辅助剂, 通过简单沉淀法合成了草酸铕Eu₂(C₂O₄)₃·10H₂O微米层状颗粒. 应用X射线衍射、X射线电子能谱、场发射扫描电子显微镜、光致发光光谱对Eu₂(C₂O₄)₃·10H₂O结构与性能进行了表征. 讨论了草酸铕微米层状颗粒可能的形成机理.     

Cu/HMOR催化二甲醚羰基化合成乙酸甲酯: 催化剂制备方法的影响 (cited: 2)

采用氨蒸发法、尿素水解法、离子交换法及浸渍法制备HMOR负载的Cu催化剂, 考察其催化二甲醚(DME)羰基化合成乙酸甲酯(MA)性能. 结果表明离子交换法制得Cu/HMOR催化剂在Cu的金属中心和酸性分子筛载体的共同作用下具有较好催化反应活性. 在210 oC、1.5 MPa、空速4883 h^-1,DME转化率为95.3%,MA选择性为94.9%. 对催化剂进行N2物理吸附、X射线衍射、NH₃程序升温脱附和CO程序升温脱附等表征发现,离子交换法制得Cu/HMOR催化剂具有较高比表面、大量弱酸及一定中强酸、适中的CO吸附强度,提高了CO插入DME羰基化反应活性.     

催化剂的性质对超临界乙醇条件下热解木质素液化的影响

研究了在超临界乙醇中、氢气存在下,一系列金属-酸双功能催化剂的酸性、孔径大小、负载的金属对热解木质素加氢裂解过程的影响．制备并采用N₂等温吸附和BET比表面、X射线衍射、NH₃-程序升温脱附技术对催化剂进行表征．实验结果表明催化剂酸性增强可促进热解木质素的缩聚反应,从而产生大量的焦炭和水,导致其液化效率降低．微孔催化剂比介孔催化剂孔径小,与强酸共同作用会导致热解木质素裂解生成更多的小分子气体．在催化剂上负载金属Ru可有效地抑制热解木质素的缩聚反应,促进其裂解液化．     

C3N4的高温高压同步辐射研究

利用激光加热金刚石对顶砧技术在高温高压条件下合成了纯beta相和立方相C₃N₄beta相C₃N₄所属对称群为P63/M (176).对石墨相与beta相C₃N₄的X射线衍射结果进行了精确分析, 得到优化晶胞参数.原位高压同步辐射X射线衍射分析表明, 在6GPa时由beta相到立方相C₃N₄的相转变已经发生, 之后两相共存直到19GPa时相变结束得到纯立方相C₃N₄.     

脉冲磁场对水热法制备Mn掺杂ZnO稀磁半导体的影响

本文以Zn(CH₃COO)₂·2H₂O, Mn(CH₃COO)₂·4H₂O和氨水缓冲溶液为原料, 在4 T脉冲磁场下利用水热法制备了Mn掺杂ZnO稀磁半导体晶体, 通过X射线衍射、 扫描电子显微镜、透射电子显微镜、拉曼光谱、荧光分光光度计及振动样品磁强计等对样品的微观结构及磁性能等进行了表征, 结果表明: Mn掺杂ZnO稀磁半导体晶体仍保持ZnO六方纤锌矿结构, 4 T脉冲磁场下合成的Mn掺杂ZnO稀磁半导体晶体具有明显的室温铁磁性, 其饱和磁化强度(M_s)为0.028 emu/g, 比无脉冲磁场下制备的样品提高一倍以上, 且4 T 脉冲磁场将样品的居里温度提高了15 K.     

Mn掺杂SiC磁性薄膜的结构表征

利用反射式高能电子衍射(RHEED)、X射线衍射(XRD)和X射线吸收近边结构谱(XANES)等技术研究了在950 ℃条件下Si(111)衬底上共蒸发分子束外延方法制备的Mn掺杂SiC磁性薄膜的结构特征.RHEED结果表明,生长的Mn掺杂SiC薄膜为立方结构.XRD和XANES结果表明,在Mn掺杂量为0.5％和18%的样品中,Mn原子均是与SiC半导体介质中的Si原子反应生成镶嵌在SiC基体中的Mn₄Si₇化合物颗粒,并未观察到在SiC晶格中有替代式或间隙式的M     

表面活性剂修饰的CuCoMn催化剂催化合成低碳醇

分别采用阳离子(十六烷基三甲基溴化铵,CTAB)、阴离子(十二烷基硫酸钠,SDS)、非离子(三嵌段共聚物,P123)三种不同类型的表面活性剂对CuCoMn基催化剂进行改性,利用N₂吸脱附、XRD、XPS、IR手段表征了催化剂的微观结构．在生物质基合成气合成高醇中的应用研究结果表明,SDS修饰的CuCoMn催化剂表现出较高的CO转化率(29.7%),而CTAB修饰的CuCoMn催化剂具有优良的高醇选择性(41.2%)．同时,三种表面活性剂修饰的催化剂均不同程度地提高了高醇产率及其在醇产     

K-Co-Mo/CNTs催化剂合成低碳醇性能研究

A series of carbon nanotubes-supported K-Co-Mo catalysts were prepared by a sol-gel method combined with incipient wetness impregnation.The catalyst structures were characterized by X-ray diffraction,N₂ adsorption-desorption,transmission electron microscopy and H₂-TPD,and its catalytic performance toward the synthesis of higher alcohols from syngas was investigated.The as-prepared catalyst particles had a low crystallization degree and high dispersion on the outer and inner surface of CNTs.The uniform mesoporous structure of CNTs increased the diffusion rate of reactants and products,thus promoting the reaction conversion.Furthermore,the incorporation of CNTs support led to a high capability of hydrogen absorption and spillover and promoted the formation of alkyl group,which served as the key intermediate for the alcohol formation and carbon chain growth.Benefiting from these characteristics,the CNTs supported Mo-based catalyst showed the excellent catalytic performance for the higher alcohols synthesis as compared to the unsupported catalyst and activated carbon supported catalyst.     

Self-assembled one-pot synthesis of red luminescent CdS:Mn/Mn(OH)2 nanoparticles

We report a novel method of growing red luminescent (635 nm) Mn-doped CdS (CdS:Mn) nanoparticles capped by an inorganic shell of Mn(OH)₂. CdSO₄, Na₂S₂O₃ and Mn(NO₃)₂ were used as the precursors, and thioglycerol (C₃H₈O₂S) was employed as the capping agent and also the catalyst of the reaction. Using these materials resulted in very slow rate of the reaction and particles growth. The self-assembled one-pot process was performed at pH of 8 and Mn:Cd ratio of 10, and took about 10 days for completion. CdS:Mn nanoparticles are slowly formed in the first day of the process; however, the luminescence is weak. After 7 days, the solution turns white turbid through the formation of additional particles, which precipitate on the walls on the next day. At this stage, a relatively strong red luminescence at 635 nm appears from transparent solution of the CdS:Mn nanoparticles. The white deposit on the walls turns to dark-brown color and luminescence increases on the 9th day. Finally, the CdS:Mn nanoparticles agglomerate and precipitate out of the solution on 10th day. X-ray diffraction and optical spectroscopy showed crystalline phase CdS nanoparticles with an average size of 3.6 nm. We explain the luminescence enhancement based on the formation of a Mn(OH)₂ shell on the surface of the CdS:Mn nanoparticles during the precipitation stage. This can passivate the S dangling bonds located on the particles surface. As the surface Cd sites are previously capped with thioglycerol molecules, a complete surface passivation is achieved and results in emergence of high-intensity luminescence.     

Selective CO oxidation in hydrogen-rich gas over CuO/CeO2 catalysts

A series of CuO/CeO₂ catalysts with different Cu-Ce compositions were synthesized by co-precipitation method and characterized by X-ray diffraction, H₂-TPR, CO-TPD, SEM and X-ray photoelectron spectroscopy (XPS) techniques. The effects of Cu-Ce composition and water vapor on the catalytic properties for the selective CO oxidation in the hydrogen-rich gas were investigated. The results indicated that CuO (10%)/CeO₂ catalyst remained the maximum CO conversion and selectivity at 140 and 160 °C, while the performance of CuO/CeO₂ catalysts deteriorated with the CuO molar ratio further increased. The interfacial CuO and CeO₂ interaction and synergistic effect enhanced the redox properties of CuO/CeO₂ catalyst and the highly dispersed copper species were proposed as the active sites for the selective CO oxidation. The blockage of catalytic active sites by absorbed water and the formation of CO-H₂O surface complexes reduced the activity of CuO (10%)/CeO₂ catalyst. The decreasing of surface lattice oxygen and absorbed oxygen species and the agglomeration of copper particles were the plausible interpretations for the deactivation of CuO (10%)/CeO₂ catalyst.     

Self-catalytic synthesis and light-emitting property of highly aligned Mn-doped Zn2SiO4 nanorods

Highly aligned Mn-doped Zn₂SiO₄ nanorods were fabricated by using a modified vapor-phase evaporation method. Their microstructure and chemical bond configurations were investigated with the help of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared absorption spectroscopy, and X-ray photoelectron spectroscopy. The formation process of the Mn-doped Zn₂SiO₄ nanorods can be elucidated on the basis of a self-catalytic vapor–liquid–solid growth mechanism in which Mn chloride hydrate acts as the catalyst and impurity source. Photoluminescence measurements revealed that an intensive green luminescence peak appears at 523 nm, which corresponds to the electronic transition ⁴T₁(⁴G)→⁶A₁(⁶S) of Mn²⁺ ions. Our experimental results provide a useful approach to directly fabricate Si-based nanoscale light-emitting materials using ZnO–Zn₂SiO₄ composite. PACS 81.05.-t; 81.10.Bk; 81.07.-b     

The performance of iron-containing catalysts prepared at low temperature for carbon monoxide hydrogenation

The performance for carbon monoxide hydrogenation of amorphous- and crystalline-unsupported iron oxides following low temperature pretreatment in nitrogen, carbon monoxide and hydrogen has been examined. The phase compositions of the catalysts before and after catalytic evaluation have been determined by⁵⁷Fe Mössbauer spectroscopy. Pretreatment of amorphous non-potassium doped precipitates gave the formation of metallic iron catalysts which were catalytically active at low temperatures and which were shown by Mössbauer spectroscopy to be converted during evaluation to iron carbide and the iron oxide Fe₃O₄. Catalysts which were not pretreated were reduced during catalytic evaluation to Fe₃O₄. Pretreated potassium-doped catalysts composed of either iron carbide or a mixture of iron carbide and metallic iron gave hydrocarbon product distributions which showed a higher Schulz-Flory alpha value and a lower selectivity towards methane when the catalyst reached steady state as a result of an increase in carbon monoxide adsorption and/or a decrease in hydrogen adsorption. The used catalysts were shown by Mössbauer spectroscopy to contain iron carbide together with various proportions of metallic iron and the iron oxide Fe₃O₄. The activities of the pretreated amorphous and crystalline catalysts were comparable and may be related to the disintegration of the crystalline catalysts during pretreatment in carbon monoxide which induces the formation of particles with surface areas similar to those observed in the amorphous catalysts.     

Structural and magnetic properties of Mn-doped anatase TiO<Subscript>2</Subscript> films synthesized by atomic layer deposition

Mn-doped anatase TiO₂ (Mn: 1.2, 2.4 at%) thin films were grown on Si(100) via atomic layer deposition (ALD). The synthesis utilized Ti(OCH(CH₃)₂)₄ and H₂O as ALD precursors and Mn(DPM)₃ as a dopant source. X-ray photoelectron spectroscopy measurements indicate that Mn is successfully doped in the TiO₂ matrix and reveal information about film composition and elemental chemical states. Microstructure, crystallinity, and density were investigated with scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. All ALD-synthesized films exhibited room-temperature ferromagnetism; the microstructure, density, and magnetic field-dependent magnetization of the TiO₂ varied with the concentration of Mn. ALD permits precise composition and thickness control, and much higher process throughput compared to alternative techniques.     

Research on Si-Al based catalysts prepared by complete liquid-phase method for DME synthesis in a slurry reactor

A series of Si-Al based DME synthesis catalysts were prepared by complete liquid-phase method and characterized by in situ XPS, XRD, N₂ adsorption and NH₃-TPD analyses. Based on the results, the addition of Si could adjust the pore structure and surface acidity of catalyst, exhibiting a strong promoting effect on the CO conversion and DME selectivity. However, when Si/Al ratio is higher, Si would cover active sites and increase the amount of strong acidity sites, causing the reduction in catalytic activity. It was found from in situ XPS characterization that Cu⁰ is the active center of methanol synthesis in DME production, and the addition of Si changes the chemical surroundings of active components and weaken the interaction between Cu, Zn and Al, which maybe give rise to the decrease in catalyst stability.     

Synthesis of coiled carbon nanotubes on Co/Al2O3 catalysts in a fluidised-bed

Mixtures of regularly coiled and straight multi-walled carbon nanotubes (MWNTs) were synthesised on alumina supported Co catalysts prepared by pH controlled, wet impregnation. The synthesis reaction was performed under C₂H₂:H₂:N₂ at 750 °C in a fluidised-bed for 30 min. Scanning electron microscopy/energy dispersive X-ray spectroscopy shows good distribution of the active Co particles on the surface of the alumina support. Determined from 10 individual SEM images from the same product batch, the CNTs present are typically from 10 to 40 nm in diameter. Thermogravimetric analysis (TGA) and Raman spectroscopy indicate the total oxidative weight loss is independent of pH during catalyst preparation. This study is the first to report the use of a fluidised-bed for the synthesis of coiled MWNTs, using alumina supported Co catalysts.