The active site of methanol synthesis over Cu/ZnO/Al2O3 industrial catalysts

One of the main stumbling blocks in developing rational design strategies for heterogeneous catalysis is that the complexity of the catalysts impairs efforts to characterize their active sites. We show how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al(2)O(3) methanol synthesis catalyst by using a combination of experimental evidence from bulk, surface-sensitive, and imaging methods collected on real high-performance catalytic systems in combination with density functional theory calculations. The active site consists of Cu steps decorated with Zn atoms, all stabilized by a series of well-defined bulk defects and surface species that need to be present jointly for the system to work.     

三氧化铝催化合成丙交酯

采用三氧化二铝作催化剂催化乳酸脱水,讨论了丙交酯制备过程中的影响因素,用重结晶法得到了高纯度的丙交酯,并通过熔点、红外光谱对丙交酯进行了表征。     

Creep-resistant, Al2O3-forming austenitic stainless steels

A family of inexpensive, Al2O3-forming, high-creep strength austenitic stainless steels has been developed. The alloys are based on Fe-20Ni-14Cr-2.5Al weight percent, with strengthening achieved through nanodispersions of NbC. These alloys offer the potential to substantially increase the operating temperatures of structural components and can be used under the aggressive oxidizing conditions encountered in energy-conversion systems. Protective Al2O3 scale formation was achieved with smaller amounts of aluminum in austenitic alloys than previously used, provided that the titanium and vanadium alloying additions frequently used for strengthening were eliminated. The smaller amounts of aluminum permitted stabilization of the austenitic matrix structure and made it possible to obtain excellent creep resistance. Creep-rupture lifetime exceeding 2000 hours at 750 degrees C and 100 megapascals in air, and resistance to oxidation in air with 10% water vapor at 650 degrees and 800 degrees C, were demonstrated.     

Ultra-low thermal conductivity in W/Al2O3 nanolaminates

Atomic layer deposition and magnetron sputter deposition were used to synthesize thin-film multilayers of W/Al(2)O(3). With individual layers only a few nanometers thick, the high interface density produced a strong impediment to heat transfer, giving rise to a thermal conductivity of approximately 0.6 watts per meter per kelvin. This result suggests that high densities of interfaces between dissimilar materials may provide a route for the production of thermal barriers with ultra-low thermal conductivity.     

X-ray diffraction study of the ultrathin Al2O3 layer on NiAl110

Ultrathin Al2O3 layers on alloys are used as templates for model catalysts, tunneling barriers in electronic devices, or corrosion-resistant layers. The complex atomic structure of well-ordered alumina overlayers on NiAl110 was solved by surface x-ray diffraction. The oxide layer is composed of a double layer of strongly distorted hexagonal oxygen ions that hosts aluminum ions on both octahedral and tetrahedral sites with equal probability. The alumina overlayer exhibits a domain structure that can be related to characteristic growth defects and is generated during the growth of a hexagonally ordered overlayer (Al2O3) on a body-centered cubic (110) substrate (NiAl).     

Al2O3陶瓷对CO2激光吸收率试验测定

试验验证了PHC-1500型CO2激光器输出激光经传输光路转换后的偏振化方向.利用设计的反射率测定装置,测定了Al2O3陶瓷表面分别对不同入射角下垂直和平行于入射面的线偏振CO2激光的反射率,据此得到Al2O3陶瓷的折射率和布儒斯特角及吸收率,与采用Fresnel公式计算获得的相应的反射率和吸收率值变化趋势一致,吻合较好.试验发现,平行于入射面的线偏振CO2激光使Al2O3陶瓷的吸收率由零度入射角时的约75%提高到布儒斯特入射角时的95%.这一结论为在开展CO2激光辅助切削Al2O3陶瓷时,设计高能量利用率的传输光路和对温度场的准确计算提供了试验和理论依据.     

KF／Al2O3催化合成2-溴-2-硝基-1，3-丙二醇

目的 采用KF/Al2O3催化剂催化合成2-溴-2-硝基-1,3-丙二醇,并确定最佳反应条件.方法 制备KF/Al2O3催化剂,用该催化剂对硝基甲烷与甲醛的羟基化反应进行催化合成,再经过溴化反应制得产物,最后由红外光谱及熔点测定对产物进行确定表征.结果经测定,产物2-溴-2-硝基-1,3-丙二醇的红外特征峰为3240 cm-1、3190 cm-1、1810 cm-1、1920 cm-1、960 cm-1、840 cm-1,熔点为126.7 ℃.当溴化反应条件固定为反应温度10 ℃,反应时间0.5 h时,KF/Al2O3催化剂对硝基甲烷与甲醛的羟基化反应的最佳反应条件为反应温度25 ℃,反应时间2 h,反应物硝基甲烷、甲醛与催化剂使用量物质量的比为2∶5∶2.在最佳反应条件下,该催化合成反应收率可达78.1%.结论 KF/Al2O3催化剂实现了对2-溴-2-硝基-1,3-丙二醇的催化合成,且反应具有收率高,操作方法简单,反应时间短,反应条件容易控制,反应对环境友好的特点.     

Polymorphism in presolar Al2O3 grains from asymptotic giant branch stars

We report microstructural and isotopic analyses of two presolar Al2O3 grains. Aluminum oxide is important cosmically, because its presence has been detected in the infrared spectra of the circumstellar envelopes of O-rich asymptotic giant branch stars and because it is predicted to be the first solid to condense in these stellar environments. The two grain structures, one corundum and the other amorphous, confirm that asymptotic giant branch stars produce both phases. The variation in structure and Ti content demonstrates that Al2O3 can condense in the absence of TiO2 seed clusters but that Ti may be important in determining the crystal structure.     

Limits for combustion in low O2 redefine paleoatmospheric predictions for the Mesozoic

Several studies have attempted to determine the lower limit of atmospheric oxygen under which combustion can occur; however, none have been conducted within a fully controlled and realistic atmospheric environment. We performed experimental burns (using pine wood, moss, matches, paper, and a candle) at 20 degrees C in O2 concentrations ranging from 9 to 21% and at ambient and high CO2 (2000 parts per million) in a controlled environment room, which was equipped with a thermal imaging system and full atmospheric, temperature, and humidity control. Our data reveal that the lower O2 limit for combustion should be increased from 12 to 15%. These results, coupled with a record of Mesozoic paleowildfires, are incompatible with the prediction of prolonged intervals of low atmospheric O2 levels (10 to 12%) in the Mesozoic.     

TiO2/MIL-53(Al)和TiO2/Al2O3催化剂的制备及其光催化性能研究

采用溶剂热法合成了MIL-53(Al),以此为载体负载TiO_2制备得到TiO_2/MIL-53(Al)光催化剂用于污水中次甲基蓝的催化降解研究,并与传统载体材料Al_2O_3负载的TiO_2催化剂的光催化效果进行比较。样品通过热重-差热扫描量热(TG-DSC)、红外光谱(FTIR)、扫描电镜(SEM)、X射线衍射(XRD)、N_2物理吸附-脱附等方法进行表征。采用光度吸收法分析污水中次甲基蓝的降解率,结果显示,TiO_2/MIL-53(Al)光催化剂对次甲基蓝的光催化降解率达到98.6%,而TiO_2/Al_2O_3光催化剂对次甲基蓝的降解率只有70.3%,TiO_2/MIL-53(Al)光催化剂对污水中次甲基蓝的降解去除能力明显优于TiO_2/Al_2O_3光催化剂对次甲基蓝的降解去除能力。     

涂层对三维碳纤维编织体/Al2O3陶瓷复合材料性能的影响

从自制的SiO2和SiC涂层/三维碳纤维编织体出发,采用溶胶浸渍-原位分解法得到三维碳纤维编织体/涂层/Al2O3陶瓷复合材料.采用等温氧化失重、XRD、SEM、电子拉伸试验等测试手段研究了涂层对碳纤维编织体抗氧化性、复合材料力学性能的影响及复合材料的强韧化机理.结果表明:涂层可明显提高碳纤维编织体的抗氧化性能;梯度SiC涂层可明显改善纤维与陶瓷颗粒的界面结合性能,使复合材料的强度、断裂韧性和弹性模量分别增加5~10倍,材料的断裂呈层间紧密的复合断裂;裂纹扩展和断口分析表明,复合材料的强韧化机理为Cf的拔出、桥接和诱导裂纹偏转.     

固体超强酸SO4^2-/ZrO2/Al2O3催化乙二胺合成哌嗪的研究

采用超声化学共沉淀法制备SO4^2-/ZrO2/Al2O3固体超强酸催化剂,并对该催化剂在常压固定床反应器中催化乙二胺合成哌嗪的性能进行了研究.结果表明,乙二胺的转化率随反应温度升高而增大,哌嗪的选择性和收率在温度超过250℃条件下急剧下降;进料速度超过0.50 mL/min后,乙二胺的转化率和哌嗪的收率急剧降低,而哌嗪的选择性与进料速度没有明显关系;乙二胺的进料质量分数不超过50%,原料转化率、哌嗪收率以及哌嗪选择性没有明显差别;但随乙二胺质量分数进一步增大,原料转化率急剧下降,而哌嗪的选择性和哌嗪的收率则下降更快.     

挤压态Cu-Al2O3弥散强化铜合金组织结构与强化机制的定量探讨

通过力学性能测试、金相和透射电镜观察等手段研究了热挤压态Cu-0.12Al2O3弥散强化铜合金的组织与性能.结果表明:挤压态Cu-Al2O3弥散强化铜合金的主要强化机制是细晶强化和弥散强化.细小的Al2O3相钉扎位错,强烈抑制基体的再结晶,造成材料小晶粒、多晶界效应,其平均亚晶粒大小仅为2~4μm.同时对不同强制机制对合金强度的贡献进行了定量计算,计算值与实验值吻合较好.     

KOH／Al2O3催化大豆油酯交换反应制备生物柴油

[目的]用固体碱催化剂催化酯交换反应制备生物柴油,以减少对环境造成的污染。[方法]以层析用中性氧化铝为载体,负载KOH并经高温焙烧处理制得KOH／Al2O3催化剂,催化大豆油酯交换反应制备生物柴油,系统地研究了催化剂的制备、酯交换反应等条件对大豆油转化率的影响。[结果]该催化剂对大豆油与甲醇酯交换反应有很高的催化活性。试验结果显示,当KOH负载量为10％,500℃焙烧3h,催化剂用量5％,醇油摩尔比12：1,酯交换反应仅2h,大豆油的转化率高达98．63％。[结论]KOH／Al2O3催化剂对大豆油与甲醇发生酯交换反应有很高的催化活性,且生产工艺简单,产品后处理方便,具有很大的应用价值。     

Ordering of V2+, Mn2+, and Fe3+ Ions in Zoisite, Ca2Al3Si3O12(OH)

The presence of very small amounts of Mn(2+), V(2+), and Fe(3+) ions in zoisite can be easily detected by the electron paramagnetic resonance technique at room temperature. The Mn(2+) and Fe(3+) ions are completely ordered and are probably located in the Ca(1)- and Al(II)-sites, respectively, whereas the V(2+) ions probably occupy both Ca(1)- and Ca(2)-sites, with a preference for the Ca(1)-site.     

活性Al2O3法与CaO＋KH2PO4法处理高氟饮用水的对比

[目的]选择适宜的高氟饮用水处理方法。[方法]针对相同的高氟饮用水水质，利用活性Al2O3吸附法与CaO＋KH2PO4沉淀法进行对比研究，并对2种除氟方法的除氟效果、处理成本、处理周期和出水量等方面作了对比。[结果]将氟化物浓度为1．75mg／L的高氟水降至1．0mg／L以下，吨水活性Al2O3和CaO＋KH2PO4的投加量分别为20．0kg和2．05kg。确定了CaO／KH2PO4的最佳投药量为0．400／0．625，在该配比下得到的水质结果为：氟质量浓度为0．86mg／L，pH值为7．02，总硬度144mg／L，硫酸盐质量浓度68．5mg／L，氯化物质量浓度为46．2mg／L，达到了饮用水水质标准。活性Al2O3吸附法较CaO＋KH2PO4沉淀法的处理周期短，设备和工程投资少，而CaO＋KH2PO4沉淀法在处理效果、出水量以及能耗方面占优势。[结论]活性Al2O3吸附法适用于原水氟化物超标倍数低，且总硬度偏低的高氟水水质；CaO＋KH2PO4沉淀法适用于原水K^＋和PO4^3-偏低的水质。     

硬质合金TiC/Al2O3/TiN复合涂层的热应力分析

采用有限元法分析了硬质合金TiC/Al2O3/TiN复合涂层的残余热应力,结果表明:iC/Al2O3/TiN复合涂层温度从800 ℃下降到0 ℃时,等效应力在TiN层内应力最高,为3 103 MPa;三轴应力在TiN涂层内以拉应力为主,最大拉应力为1 844 MPa,在硬质合金基体内以压应力为主,其最大压应力为-1 194 MPa;TiC层内拉应力比TiN层内略小,l2O3层为一应力低谷,夹在2个高峰之间;在刀片边缘应力相对较小,在刀片表面的中心应力相对集中.     

制备γ-Fe2O3纳米微粒的一种新方法

提出了两次反应制备γ-Fe2O3纳米微粒的新方法.制备过程中通过控制第2次反应中NaOH的浓度实现了由结晶的FeOOH逐渐转化为结晶的γ-Fe2O3纳米微粒.用X射线衍射仪(XRD)、透射电子显微镜(TEM)和振动样品磁强计(VSM)分别对纳米微粒的晶体结构、形态和大小、磁化强度进行表征.实验结果表明,γ-Fe2O3纳米微粒具有高结晶性,形状近似为球形,饱和磁化强度达63.90 A·m2/kg,是γ-Fe2O3块体饱和磁化强度的84.1%.     

超声化学共沉淀法制备SO4^2-/ZrO2/Al2O3固体酸及其催化作用

采用超声化学共沉淀法制备SO4^2-/ZrO2/Al2O3固体超强酸催化剂,采用FT-IR、TG-DTG对催化剂进行了表征,并对催化剂的酸性强度及催化乙二胺合成哌嗪的性能进行了研究．结果表明,该催化剂具有桥式双配位结构,该结构在温度超过700℃时被破坏;随浸渍溶液浓度增大,催化剂的酸性强度和含硫量均先增大后减小;随陈化时间增加,催化剂的酸性强度增大,但陈化时间超过9h后,催化剂的酸性强度没有明显变化;焙烧温度不超过550℃时,催化剂的酸性强度随焙烧温度升高而增强,但温度超过550℃后,催化剂的酸性强度随焙烧温度升高反而降低;随催化剂中Al摩尔分数的增大,催化剂的酸性强度先增大后减小．引入Al对于提高乙二胺的转化率、改善哌嗪的收率和选择性具有一定的作用,并且哌嗪的收率和选择性随Al含量的增大而增大．