温度对α-Al2O3(0001)表面吸附生长ZnO影响的DFT研究

The adsorption and the growth of ZnO on α-Al2O3(0001) surface at various temperatures were theoretically calculated by using a plane wave pseudopotentials (USP) method based on density functional theory.The average adsorption energy of ZnO at 400, 600 and 800 ℃ is 4.16±0.08, 4.25±0.11 and 4.05±0.23 eV respectively. Temperature has a remarkable effect on the structure of the surface and the interface of ZnO/α-Al2O3(0001). It is found that the Zn-hexagonal symmetry deflexion does not appear during the adsorption growth of ZnO at 400 ℃, and that the ZnO10-10 is parallel with the 10-10 of the α-Al2O3(0001), which is favorable for forming ZnO film with the Zn-terminated surface. It is observed from simulation that there are two kinds of surface structures in the adsorption of ZnO at 600 ℃: one is the ZnO surface that has the Zn-terminated structure, and whose 10-10 parallels the 10-10 of the substrate surface, and the other is the ZnO10-10 //sapphire 11-10 with the O-terminated surface. The energy barrier of the phase transition between these two different surface structures is about 1.6 eV, and the latter is more stable. Therefore,the suitable temperature for the thin film growth of ZnO on sapphire is about 600 ℃, and it facilitates the formation of wurtzite structure containing Zn-O-Zn-O-Zn-O double-layers as a growth unit-cell. At 600 ℃, the average bond length of Zn-O is 0.190±0.01 nm, and the ELF value indicates that the bond of (substrate)-O-Zn-O has a distinct covalent character, whereas the (Zn)O-Al (substrate) shows a clear character of ionic bond. However, at a temperature of 800 ℃, the dissociation of Al and O atoms on the surface of the α-Al2O3(0001) leads to a disordered surface and interface structure. Thus, the Zn-hexagonal symmetry structure of the ZnO film is not observed under this condition     

α-Al2O3(0001)表面弛豫及其对表面电子态的影响

The relaxation and electronic structure of the α-Al2O3 (0001) super-cell (2×2) surface with single Al atoms layer-terminated are studied using ab initio quantum-mechanical calculations based on the density functional theory and pseudo potential method. The calculations employ slab geometry and periodic boundary conditions, with the occupied orbitals expanded in plane waves. It is found that the surface relaxation results in the change of surface electronic states by investigating the relaxation and the population of the Al-O atoms of the surface. By analyzing the difference of the density of state and electron charge density between the unrelaxed and relaxed surface, it is obvious that the α-Al2O3 (0001) crystal surface appears on the O-surface state from which is most contribution to the O2p states, and the surface electronic density plotted by electron localization function (ELF) shows the characteristics of surface bonding atoms. The ELF indicates the outmost Al-O ionic bonds of the relaxed surface are much stronger than that of the unrelaxed surface.     

柔性α-Al2O3纳米结构纤维的制备与表征

制备了致密柔性的α-Al2O3,纳米结构纤维,并表征了纤维的微观结构和断裂强度及断裂伸长率等力学性质,讨论了影响纤维性能的因素,实验结果表明,纤维由厚度为30～50 nm 的纳米片构成,没有孔洞和裂纹,具有良好的抗热震性,同商品α-Al2O3纤维相比具有较高的断裂强度及断裂伸长率.     

改良拜耳法制备超细片状α-Al2O3

为对冶金级氧化铝生产工艺进行优化,采用改良拜耳法生产利润更高的片状α-Al2O3。讨论分析了铝酸钠溶液除杂、球形晶种强化碳分聚附、水热深度脱钠及在添加AlF3晶种条件下煅烧对制备片状α-Al2O3的影响。通过XRF、XRD和SEM对产物的成分、物相及形貌进行了分析,结果表明:除杂过程中工业氢氧化铝、氧化钙、草酸钠添加量分别为45、10、10g/L时杂质铁、硅、镁、锌、钙的含量分别降至15、50、18、15、5.2 ppm;强化碳分聚附中添加少量的球形晶种,溶液的分解率达到92%以上,产物粒度降低且分布均匀;水热深度脱钠中降低pH促进三水铝石向一水软铝石转化的过程更加彻底,且在pH=1时Na2O含量低至0.0163%;在850℃下对洗涤后的水热产物煅烧4h,当AlF3晶种添加量为2%,可得纯度大于99.96%,形貌规则的超细片状α-Al2O3。     

α-Al2O3与Co-Ni合金电化学共沉积动力学模型

在经典复合电沉积机理基础上,考虑到粒子与电极表面之间的多种作用力,以吸附强度来表征粒子与电极表面的作用力大小,根据粒子在电极表面的临界吸附强度,把粒子的吸附分为有效吸附和非有效吸附.当吸附强度大于临界吸附强度时,粒子能被有效吸附嵌入到沉积层中,粒子被有效吸附的概率和平均吸附强度有关.建立了相应的复合电沉积动力学模型.该模型在α-Al2O3与Co-Ni合金的复合共沉积体系中,在电流密度为l～20A@dm2范围内得到了验证.通过数学模型和实验结果研究了电流密度对粒子沉积量ψc、吸脱附常数K、有效吸附概率P和平均吸附强度的影响规律.     

TiO2-Al2O3作为Mo催化剂担体的研究

Tio。－AI。oa二元氧化物的制备at艺大体可分为两种．一种是利用液相浸渍或气相沉积方法将Tio。担载在AI。0。上，使Tio。主要覆盖在AI。0。表面上［‘－1另一种是通过Ti盐和AI盐混合溶液共沉淀方法使Tio。和AI。0。均匀混合在一起【‘－’1．不同的制备工艺对Tio。－AI。03的表面结构和表面性质有很大影响问．我们曾报导用TICly蒸气化学气相沉积方法制备出了D02在1川2O3表面呈现十分均匀分布的DoZ一周。03复合氧化物担体＊’1．本文进一步考察D0。在周。0。表面的沉积对川。0。孔结构的影响，以及Ti02－A1203作为加氢精制MO催…     

添加贵金属的Ni/α-Al2O3催化剂甲烷部分氧化制合成气的研究

甲烷部分氧化制合成气因其高空速、高转化率、低H2/CO比而引起人们的重视[1～5].本文研究了在Ni/α-Al2O3催化剂中添加的Rh、Ru、Pt和Pd等贵金属在甲烷部分氧化制合成气反应中的催化作用,重点研究了添加Pt对Ni/α-Al2O3催化剂反应性能的影响.     

用金属有机化合物燃烧化学沉积α-Al2O3纳米陶瓷膜

提出了直接在空气中沉积纳米陶瓷薄膜的新方法———燃烧化学沉积法。以沉积αAl2O3为例,用异醇铝溶于易燃溶剂甲苯中形成原始溶液,将该溶液雾化并穿过氧乙炔火焰,在火焰前方的基体上形成了αAl2O3纳米陶瓷薄膜。提出了火焰体系化学反应的相变动力学公式,按完全燃烧原理和流体连续方程计算出专用喷嘴的原料液体流量及氧压力,并进行雾化试验,确定出合理的耗氧量,对可能由于工艺参数不合适导致的不均匀生长进行了分析,提出了合理的工艺参数。结果表明,用金属有机化合物溶于易燃溶剂中进行燃烧制备纳米陶瓷薄膜的工艺方法是可行的。     

纳米α-Al2O3粉体的制备与表征

以硫酸铝铵为原料,可溶性淀粉为分散剂,分别利用固相法和湿化学法制备了纳米α-Al2O3粉体。产品经超声波处理后,X-射线衍射实验证明为α相,用透射电子显微镜(TEM)测得粉体呈球形,粒径为20nm-30nm。利用大分子链的空间位阻效应,高分子网络的阻融作用,以及固体分散剂的物理分散作用,克服了粉末的粘连与团聚。     

α-Al2O3与Co-Ni合金电化学共沉积动力学模型

在经典复合电沉积机理基础上,考虑到粒子与电极表面之间的多种作用力,以吸附强度来表征粒子与电极表面的作用力大小,根据粒子在电极表面的临界吸附强度,把粒子的吸附分为有效吸附和非有效吸附.当吸附强度大于临界吸附强度时,粒子能被有效吸附嵌入到沉积层中,粒子被有效吸附的概率和平均吸附强度有关.建立了相应的复合电沉积动力学模型.该模型在α-Al2O3与Co-Ni合金的复合共沉积体系中,在电流密度为1～20 A•dm2范围内得到了验证.通过数学模型和实验结果研究了电流密度对粒子沉积量φc、吸脱附常数K、有效吸附概率P和平均吸附强度的影响规律.     

硝酸镁在γ-Al2O3上的热分解及MgO/γ-Al2O3

研究了不同载量时Mg(NO     

异丁烷脱氢V2O5/γ-Al2O3催化剂的研究

五氧化二钒;异丁烷脱氢V2O5/γ-Al2O3催化剂的研究     

NOx储存催化剂Pt/BaAl2O4-Al2O3的XAFS研究

采用共沉淀-浸渍法在不同载体焙烧温度下,制备了不同Al/Ba原子比的Pt/BaAl2O4-Al2O3系列样品.用XRD, XANES, EXAFS,以及NSC (NOx storage capacity）测定等手段对样品的微观结构和NOx储存性能进行了详细的表征.样品中Ba物种是以BaAl2O4和BaCO3两种混合物相的形式存在,且伴随着载体焙烧温度和Ba含量的降低, BaAl2O4物相的分散度变高, NOx储存活性也随之提高,这表明BaAl2O4相的分散度与样品的NOx储存性能密切相关,小颗粒的BaAl2O4相是NOx的主要储存活性中心.在样品中, Pt物种以金属原子簇形式存在,分散度很高,其Pt－Pt壳层配位数较标样Pt粉有显著下降, Pt－Pt键长变短,出现了纳米收缩现象.高分散的小颗粒金属Pt原子簇为捕获和氧化NOx的主要活性中心.     

Environment-friendly synthesis of N-phenylpiperidine from aniline and 1,5-pentanediol over γ-Al2O3 catalyst

An efficient environment-friendly synthesis of N-phenylpiperidine was developed from aniline and 1,5-pentanediol over γ-Al2O3 catalyst under atmospheric pressure. The conversion of 1,5-pentanediol reached 97% and the selectivity for N-phenylpiperidine attained 94%. The structure of the catalyst was characterized by NH3-TPD and BET. The influences of calcination temperature of the catalyst and reaction temperature on activity and selectivity of the catalyst were investigated.     

A Novel Way to Prepare γ-Al2O3 Supported SO42-/ZrO2 Solid Superacid Catalysts for n-Butane Isomerization

Highly active solid superacid catalysts for n-butane isomerization, SZ/Al2O3-P, were prepared by supporting SO42-/ZrO2 (SZ) on γ-Al2O3 carrier using a precipitation method.The activities of some catalysts were enhanced significantly.The activity of the most active sample, 60%SZ/Al2O3-P, was even about 2 times more active than that of the SZ catalyst.     

NiO/γ-Al2O3催化剂中NiO与γ-Al2O3间的相互作用

利用溶胶－凝胶法制备了不同含量的 ＮｉＯ／γ－Ａｌ_２Ｏ_３催化剂,通过ＸＲＤ,ＸＰＳ和 ＴＰＲ等技术考察了制备方法、ＮｉＯ含量和焙烧温度对催化剂结构和Ｎｉ存在状态的影响,发现溶胶－凝胶法制备的催化剂活性组分ＮｉＯ与担体γ－Ａｌ_２Ｏ_３间具有强相互作用．详细地讨论了Ｎｉ物种的还原状态与以“Ｎｉ~０”为活性中心的催化反应的活性之间的关系．溶胶－凝胶法制备的催化剂经高温焙烧后,Ｎｉ以一种类尖晶石结构的固溶体形式存在,这种固溶体态尖晶石可能会抑制Ｎｉ的烧结和流失,提高催化剂的稳定性．     

TiO2-Al2O3复合载体的比较研究

对用混胶法和共沉淀法分别制备的ＴｉＯ２－Ａｌ２Ｏ３复合载体（ＴｉＯ２含量为０．０８ｇ／ｇγ－Ａｌ２Ｏ３）进行了对比研究，采用的表征方法有ＸＲＤ，ＸＲＳ，ＬＲＳ等，得出的结论如下：两种载体均保持了γ－Ａｌ２Ｏ３的骨架结构，但ＴｉＯ２的分散状态不尽相同，混胶样品中ＴｉＯ２主要以表面富集的形式分散在γ－Ａｌ２Ｏ３表面，这有利于集二者的优点于一体，共沉淀样品中ＴｉＯ２趋于整个体相均匀分散，这有利于相互作用     

MoO3/TiO2-Al2O3对H2S吸附的XPS研究

应用ＸＰＳ对ＭｏＯ３／ＴｉＯ２－Ａｌ２Ｏ３体系的ＭｏＯ３在ＴｉＯ２－Ａｌ２Ｏ３载体上的存在状态及其对Ｈ２Ｓ的吸附和脱附性能进行了表征，结果表明：ＭｏＯ３在ＴｉＯ２－Ａｌ２Ｏ３表面存在分散状态的不同，这导致了对Ｈ２Ｓ吸附性能的不同，在相同的条件下，吸附剂的０．１５ｇＭｏＯ３／ｇＴｉＯ２－Ａｌ２Ｏ３时具有最大载硫量，且随吸附温度的升高载硫量也增加，达饱和对Ｓ／Ｍｏ原子比接近１，较好的氧化脱附温度为１５     

改性γ-Al2O3微填充柱色谱分析氢同位素

使用Cr2O3改性后的γ-Al2O3微填充色谱柱,分析了He、H2、HD、D2混合气体.结果表明,经改性后的γ-Al2O3柱对氢同位素分析的谱图在峰型、保留时间、柱效等方面明显优于未经改性的γ-Al2O3柱.在柱温77.4 K、氖载气流速30 mL/min、进样量5~100 μL条件下,氢同位素各组分线性关系良好,谱峰...