磁性纳米催化剂的研究进展

介绍了磁性纳米催化剂的特性,综述了近年来磁性纳米催化剂在在氢化催化、加氢甲酰化催化、C-C键偶联反应催化、氧化和环氧化催化、酯化反应催化、缩合反应催化、烯烃复分解催化、光催化、生物催化等领域应用的研究进展,旨在探讨磁性纳米催化剂制备方法和应用领域,同时提出其应用过程中存在的问题,并对发展前景进行了展望。     

炭材料负载Pt催化肉桂醛选择性加氢性能的研究

采用液相还原法分别制备了碳纳米管(MWCNT)、活性炭(AC)、碳纳米纤维(CNF)和炭气凝胶(CA)负载质量分数3%的Pt催化剂,并对催化剂的结构和形貌进行了XRD和TEM等表征。以肉桂醛加氢作为探针反应,研究了其催化肉桂醛加氢的活性和产物选择性。结果表明,炭材料的结构对其催化肉桂醛加氢行为具有重要影响,纳米炭材料催化剂（Pt/MWCNT、Pt/CNF）表现出较高的CO选择性加氢行为,而无定形碳催化剂表现为C=C选择性加氢,同时Pt/MWCNT的催化活性最高。     

碱基调控Pt纳米晶构型及其催化加氢性能

贵金属纳米晶对加氢反应具有良好的催化性能,特别是Pt纳米晶,其催化活性和选择性与纳米晶的纳米结构(形貌和尺寸)密切相关。由Gibbs-Wulff晶体生长定律可知,通过加入特定结构的封端剂可以有效控制纳米晶的形貌和尺寸。本文采用Na BH4在水溶液中还原Pt的前体H2Pt Cl6制备Pt纳米晶,并将其用于催化对硝基苯酚(p-NIP)的加氢反应。实验系统研究了碱基分子(如腺嘌呤A、鸟嘌呤G、胸腺嘧啶T、胞嘧啶C)及对应的核苷分子对Pt纳米晶构型和催化加氢活性的调控规律。研究发现,碱基分子和核苷分子对于Pt纳米晶的形貌以及尺寸具有明显的调控作用,通过不同结构生物分子的精密调控,实验制备得到了形貌和尺寸各异的Pt纳米晶。同时,所得Pt纳米晶在p-NIP的加氢反应中表现出了精密可调的催化性能。鸟嘌呤核苷、腺嘌呤核苷、β-胸腺嘧啶核苷调控制备的Pt纳米催化剂的TOFave均可达到无调控剂制备得到的催化剂的两倍以上,其中腺嘌呤核苷调控制备得到的Pt催化剂性能最好。     

纳米复合氧化物催化剂研究进展

由于纳米材料催化剂具有独特的结构及表面特性，特别是纳米复合氧化物催化剂具有氧化物催化剂的复合效果及性能，因而其催化活性和选择性大大高于传统催化剂。综述了纳米复合氧化物催化剂的特性及制备方法，介绍了国内外纳米复合氧化物催化剂的应用研究状况，如在催化加氢、催化氧化、聚合反应和环境保护等方面的应用实例及研究成果。     

催化加氢制备4,4′-ODA研究进展

综述了催化加氢制备4,4′-二氨基二苯醚(4,4′-ODA)的研究进展，重点介绍了加氢催化剂、催化工艺和溶剂的选择。负载型镍(Ni)基催化剂、包覆Ni纳米颗粒催化剂和非晶态Ni-B合金催化剂均表现出优异的加氢活性和选择性，有望取代传统的贵金属加氢催化剂。混合溶剂比单一溶剂更理想，可以提高产品的收率和纯度。未来的发展重点是开发催化加氢连续化生产工艺及相应的催化剂，以降低生产成本，提高产品质量。     

纳米催化剂的制备及应用的研究进展

介绍纳米催化剂的特性和制备方法，详述纳米催化剂在催化加氢，电化学反应，电池和环境保护等领域的应用前景。     

钯纳米颗粒制备方法的研究进展

钯纳米颗粒近年来在偶联反应、催化加氢和氧化等反应中被广泛应用,并且被用于储氢材料和燃料电池催化电极等领域。在多相催化领域中,纳米技术能够通过改变金属钯的尺寸和形貌来提高其利用率和催化活性,而制备方法是决定钯纳米颗粒性能的关键。从钯纳米颗粒在催化领域的应用方面对近年来钯纳米催化剂的制备方法进行了综述。     

纳米莫来石强化龙泉青瓷胎体性能

在龙泉青瓷胎体中引入纳米莫来石晶粒作为增强相强化龙泉青瓷,分析了纳米莫来石晶粒的添加量对龙泉青瓷力学性能、物相组成及显微结构的影响规律。研究结果表明,在龙泉青瓷胎体中引入纳米莫来石晶粒,通过颗粒增韧和裂纹增韧机理而增加龙泉青瓷的力学性能。当纳米莫来石晶粒的引入总量为3%时,其抗折强度可以达到59.7 MPa,相对于未引入纳米莫来石晶粒的青瓷样品其抗折强度增幅达85.4%。     

负载型NiO和CoO催化剂上N2O分解研究

本研究在对多种金属氧化物催化剂进行初步筛选的基础上，研制出以莫来石为载体的负载型NiO、CoO催化剂，考察了分解温度、催化剂组成和负载量对N2O分解率的影响，并对其分解反应动力学进行了研究。结果表明莫来石负载NiO、CoO催化剂对N2O分解有良好的催化性能；其反应速度对N2O均为一级反应；同样负载量下NiO有更好的催化分解活性；这一研究为开发阻力低、催化性能好的工业用蜂窝型规整填料奠定了基础。     

以塑性材料为载体的新型钯／铑纳米催化剂

Chem．Commun报道了一种新型的负载于塑性材料上的钯和铑纳米催化剂，在超临界CO2体系中催化加氢反应。     

莫来石晶粒柱状生长对莫来石基陶瓷力学性能的影响

将AlF3加入莫来石(莫来石/氧化锆)先质中,生坯试样经密闭处理及常压烧结,可获得莫来石柱状晶粒生长.实验结果表明:莫来石柱状生长使莫来石陶瓷在其强度不下降的前提下,韧性提高,且随柱状晶粒粒径增大而增加有类似架桥作用.ZTM(含AlF3)材料韧性的提高是由于莫来石柱状晶粒生长使t-ZrO2形态发生了变化,具有较大长径比或有尖角的不规则形态的t-ZrO2晶粒容易发生应力诱导相变,使材料力学性能得到明显提高.     

Structure Refinement of Mullite by the Rietveld Method and a New Method for Estimation of Chemical Composition

The structure of mullite was refined by the Rietveld method, and a new method for the estimation of chemical composition of mullite was proposed. Mullites were synthesized by firing the starting materials prepared by sol–gel and spray pyrolysis methods at various temperatures. Linear correlations were recongnized between the chemical composition of mullite analyzed with the Rietveld method and the lengths of a and b axes, but a small anomaly was found in the variation of the c axis. It was found to be caused by a difference in the c axis of pseudotetragonal mullite and that of orthorhombic mullite. A good correlation was found between the chemical composition of mullite and the intensity ratio of ( I ₂₂₀/ I ₁₁₁). This is a much more convenient method for estimating the chemical composition of mullite than Cameron's method, which uses a lattice constant.     

High-Temperature Compressive Creep of Polycrystalline Mullite

Aluminosilicates of three compositions with mullite as the major phase were synthesized by a sol-gel process and characterized with bulk and microchemical analyses and microstructural observation. An apparatus for measuring the compressive creep up to 1900 K with a sensitivity of ±1 μm was constructed and used to measure the creep of singlephase mullite, mullite with second-phase glass, and mullite with second-phase corundum. Measurements in air at stresses of 15 to 100 MPa and temperatures of 1471 to 1724 K determined that samples with second-phase glass crept more rapidly than single-phase mullite or mullite with secondphase corundum. The apparent creep activation energies determined at 100 MPa were 742 kJ/mol for the mullite containing glass, 819 kJ/mol for the single-phase mullite, and 769 kJ/mol for the mullite with second-phase corundum. The stress exponents determined at 1724 K were 1.6 for the mullite plus glass, 1.5 for the single-phase mullite, and 1.2 for the mullite with α-Al₂O₃. The creep behavior of the aluminosilicates containing glass were consistent with rate control by the viscous flow of the glass and the measured creep rates were in good agreement with creep rates calculated from a model by Dryden. The creep behavior of the completely crystalline aluminosilicates was consistent with rate control by diffusional creep.     

Evolution of Mullite Texture on Firing Tape-Cast Kaolin Bodies

Kaolin undergoes a series of phase changes on heating to elevated temperature, proceeding through kaolin, metakaolin, γ-Al₂O₃ spinel, and mullite. The morphologic evolution of the kaolin–mullite reaction series was investigated in the present study. A highly textured kaolin green body was prepared by a tape-casting technique, and the morphology evolution from kaolin flakes to mullite aciculars on firing from 450° to 1600°C was then monitored using X-ray diffractometry and scanning electron microscopy. Equiaxed mullite nuclei first appeared at 1000°C; the aspect ratio of the mullite grains then increased with increased firing temperature. The mullite aciculars rearranged their orientation in a glassy phase until they impinged on each other. A highly textured mullite specimen was prepared by firing the kaolin tape at a temperature >1500°C.     

Development of Textured Mullite by Templated Grain Growth

Highly textured mullite was obtained by enhancing anisotropic grain growth by TiO₂ doping and by templating grain growth on oriented acicular mullite seed particles in a mullite precursor. Upon heating, the mullite precursor crystallized and densified to an equiaxed microstructure of 1-2 µm mullite grains at which time the mullite seed particles grew rapidly in the length direction ( c -axis) to produce a highly textured microstructure. By changing the seed (template) particle concentration, a range of oriented microstructures and anisotropic grains could be produced.     

保温时间对废催化裂化平衡剂合成莫来石的影响

采用X射线粉末衍射和扫描电子显微镜研究了保温时间对废催化裂化平衡剂合成莫来石的影响。结果表明，二次莫来石化反应发生在1 450 ℃，保温3 h后，莫来石质量分数达94%，晶体发育良好；当保温时间超过4 h，由于反应物中Si4+被Al3+取代，导致空位增多，过渡金属进入结构的空位，使莫来石熔点降低，表现为保温时间越长，液相越多，莫来石晶体粘结于液相之中，使机械性能降低。由此可见，保温时间对二次莫来石生成反应影响较大。     

莫来石结合Al2O3-SiC浇注料的显微结构特征

借助SEM和EDAX研究了莫来石结合Al2O3 -SiC浇注料的显微结构特征。结果表明 :在莫来石结合Al2 O3 -SiC浇注料中 ,莫来石相与填充在其间隙的玻璃相形成连续基质 ;刚玉颗粒与基质中SiO2 反应生成的二次莫来石与基质中的原生莫来石交错存在 ,构成网状结构 ;SiC颗粒表面高温氧化生成的SiO2 膜 ,改善了SiC颗粒与基质的润湿性 ,是其与基质直接结合的媒介。     

Anisotropic Grain Growth in Mullite Powders as a Result of High-energy Ball Milling

High-energy ball milling was applied to a commercial mullite powder, which had a particle size ranging from 2 to 10 μm, and was considerably refined to be <1 μm after milling for 10 h. Anisotropic grain growth of mullite was observed in the milled mullite powder, starting at relatively low temperatures (1200°C). The anisotropic grain growth was possibly attributed to the special anisotropic structure of mullite and refined mullite powder as a result of the high-energy ball milling, although other factors, such as lattice defects, localized stress of the milled powder, and impurities or contaminations caused by the high-energy milling also could be factors. This anisotropic grain growth of mullite might be useful in the fabrication of reinforced ceramics based on mullite and other materials.     

Reaction sintering of alumina/mullite nanocomposites from nano-sized starting powders

Alumina/mullite ceramic nanocomposites were prepared by the mixtures of nano-sized starting powders of alumina with silica and alumina with silicon carbide. Silica from deliberate addition and as the product of silicon carbide oxidation reacted completely with alumina to form mullite. Silica from direct addition segregated at the grain boundary and intergranular mullite was formed whereas silica from oxidation was surrounded by alumina matrix and intragranular mullite was formed after reaction sintering. The most significant difference was fracture behaviour where intragranular mullite nanoparticles promoted transgranular fracture in alumina matrix due to thermal mismatch around nanoparticles and intergranular mullite nanoparticles gave rise to intergranular fracture similar to pure alumina. Wear resistance of the nanocomposites was better than that of alumina. Pull-out formation in the nanocomposites was less and pull-out size was also smaller. Fracture toughness of the nanocomposites was significantly higher than that of alumina.     

原位合成莫来石晶须及其微观结构的研究

本文通过以高岭土、工业氢氧化铝为原料,添加适量AlF3和V2O5,在高温下原位合成了莫来石晶须,采用扫描电镜（SEM）研究了合成的莫来石晶须的微观形貌,探讨了莫来石晶须的生长机理,并讨论了影响莫来石晶须生长的相关因素.在综合考虑影响莫来石晶须生长的相关因素后,制备出晶须多、长径比大、分布均匀的莫来石晶须样品.