Atomic imaging of nucleation of trimethylaluminum on clean and H2O functionalized Ge(100) surfaces

The direct reaction of trimethylaluminum (TMA) on a Ge(100) surface and the effects of monolayer H(2)O pre-dosing were investigated using ultrahigh vacuum techniques, such as scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). At room temperature (RT), a saturation TMA dose produced 0.8 monolayers (ML) of semi-ordered species on a Ge(100) surface due to the dissociative chemisorption of TMA. STS confirmed the chemisorption of TMA passivated the bandgap states due to dangling bonds. By annealing the TMA-dosed Ge surface, the STM observed coverage of TMA sites decreased to 0.4 ML at 250?°C, and to 0.15 ML at 450?°C. XPS analysis showed that only carbon content was reduced during annealing, while the Al coverage was maintained at 0.15 ML, consistent with the desorption of methyl (-CH(3)) groups from the TMA adsorbates. Conversely, saturation TMA dosing at RT on the monolayer H(2)O pre-dosed Ge(100) surface followed by annealing at 200?°C formed a layer of Ge-O-Al bonds with an Al coverage a factor of two greater than the TMA only dosed Ge(100), consistent with Ge-OH activation of TMA chemisorption and Ge-H blocking of CH(3) chemisorption. The DFT shows that the reaction of TMA has lower activation energy and is more exothermic on Ge-OH than Ge-H sites. It is proposed that the H(2)O pre-dosing enhances the concentration of adsorbed Al and forms thermally stable Ge-O-Al bonds along the Ge dimer row which could serve as a nearly ideal atomic layer deposition nucleation layer on Ge(100) surface.     

Molecular layer deposition of aluminum alkoxide polymer films using trimethylaluminum and glycidol

Molecular layer deposition (MLD) of aluminum alkoxide polymer films was examined using trimethlyaluminum (TMA) and glycidol (GLY) as the reactants. Glycidol is a high vapor pressure heterobifunctional reactant with both hydroxyl and epoxy chemical functionalites. These two different functionalities help avoid "double reactions" that are common with homobifuctional reactants. A variety of techniques, including in situ Fourier transform infrared (FTIR) spectroscopy and quartz crystal microbalance (QCM) measurements, were employed to study the film growth. FTIR measurements at 100 and 125 °C observed the selective reaction of the GLY hydroxyl group with the AlCH(3) surface species during GLY exposure. Epoxy ring-opening and methyl transfer from TMA to the surface epoxy species were then monitored during TMA exposure. This epoxy ring-opening reaction is dependent on strong Lewis acid-base interactions between aluminum and oxygen. The QCM experiments observed linear growth with self-limiting surface reactions at 100-175 °C under certain growth conditions. With a sufficient purge time of 20 s after TMA and GLY exposures at 125 °C, the mass gain per cycle (MGPC) was 19.8 ng/cm(2)-cycle. The individual mass gains after the TMA and GLY exposures were also consistent with a TMA/GLY stoichiometry of 4:3 in the MLD film. This TMA/GLY stoichiometry suggests the presence of Al(2)O(2) dimeric core species. The MLD films resulting from these TMA and GLY exposures also evolved with annealing temperature to form thinner conformal porous films with increased density. Non-self-limiting growth was a problem at shorter purge times and lower temperatures. With shorter purge times of 10 s at 125 °C, the MPGC increased dramatically to 134 ng/cm(2)-cycle. The individual mass gains after the TMA and GLY exposures in the CVD regime were consistent with a TMA/GLY stoichiometry of 1:1. The MGPC decreased progressively versus purge time. This behavior was attributed to the removal of reactants that could lead to CVD and the instability of the surface species after the reactant exposures. These results reveal that the TMA and GLY reaction displays much complexity and must be carefully controlled to be a useful MLD process.     

Potential Precursor Alternatives to the Pyrophoric Trimethylaluminium for the Atomic Layer Deposition of Aluminium Oxide

New precursor chemistries for the atomic layer deposition (ALD) of aluminium oxide are reported as potential alternatives to the pyrophoric trimethylaluminium (TMA) which is to date a widely used Al precursor. Combining the high reactivity of aluminium alkyls employing the 3-(dimethylamino)propyl (DMP) ligand with thermally stable amide ligands yielded three new heteroleptic, non-pyrophoric compounds [Al(NMe₂)₂(DMP)] ( 2 ), [Al(NEt₂)₂(DMP)] ( 3 , BDEADA) and [Al(NiPr₂)₂(DMP)] ( 4 ), which combine the properties of both ligand systems. The compounds were synthesized and thoroughly chemically characterized, showing the intramolecular stabilization of the DMP ligand as well as only reactive Al−C and Al−N bonds, which are the key factors for the thermal stability accompanied by a sufficient reactivity, both being crucial for ALD precursors. Upon rational variation of the amide alkyl chains, tunable and high evaporation rates accompanied by thermal stability were found, as revealed by thermal evaluation. In addition, a new and promising plasma enhanced (PE)ALD process using BDEADA and oxygen plasma in a wide temperature range from 60 to 220 °C is reported and compared to that of a modified variation of the TMA, namely [AlMe₂(DMP)] (DMAD). The resulting Al₂O₃ layers are of high density, smooth, uniform, and of high purity. The applicability of the Al₂O₃ films as effective gas barrier layers (GBLs) was successfully demonstrated, considering that coating on polyethylene terephthalate (PET) substrates yielded very good oxygen transmission rates (OTR) with an improvement factor of 86 for a 15 nm film by using DMAD and a factor of 25 for a film thickness of just 5 nm by using BDEDA compared to bare PET substrates. All these film attributes are of the same quality as those obtained for the industrial precursor TMA, rendering the new precursors safe and potential alternatives to TMA.     

Effect of atomic layer deposition coatings on the surface structure of anodic aluminum oxide membranes

Anodic aluminum oxide (AAO) membranes were characterized by UV Raman and FT-IR spectroscopies before and after coating the entire surface (including the interior pore walls) of the AAO membranes by atomic layer deposition (ALD). UV Raman reveals the presence of aluminum oxalate in bulk AAO, both before and after ALD coating with Al2O3, because of acid anion incorporation during the anodization process used to produce AAO membranes. The aluminum oxalate in AAO exhibits remarkable thermal stability, not totally decomposing in air until exposed to a temperature >900 degrees C. ALD was used to cover the surface of AAO with either Al2O3 or TiO2. Uncoated AAO have FT-IR spectra with two separate types of OH stretches that can be assigned to isolated OH groups and hydrogen-bonded surface OH groups, respectively. In contrast, AAO surfaces coated by ALD with Al2O3 display a single, broad band of hydrogen-bonded OH groups. AAO substrates coated with TiO2 show a more complicated behavior. UV Raman results show that very thin TiO2 coatings (1 nm) are not stable upon annealing to 500 degrees C. In contrast, thicker coatings can totally cover the contaminated alumina surface and are stable at temperatures in excess of 500 degrees C.     

Measuring the heat evolved from individual reaction steps in atomic layer deposition

A thermopile has been constructed for detecting heat of reaction during the individual steps taking place in the growth cycles of atomic layer deposition (ALD). The thermopile sensor consists of 64 junctions of thermocouple type K. It has successfully been applied to characterize ALD growth of Al₂O₃ from Al(CH₃)₃ (TMA) and H₂O, and has furthermore been applied to explore energetics of ALD growth for the following combinations of precursors: TMA + O₃, TMA + O₂, TMA + hydroquinone, TiCl₄ + H₂O, and Zn(CH₃CH₂)₂ + H₂O. The thermopile clearly identifies exo/endothermal reaction steps, the effect of surface temperature on exposure to precursors from cold sources as well as variation in the flow of gases, and allows setting up of experiments where variations in precursors and pulsing parameters may provide mechanistic insight into the ALD growth. The sensor represents a new and complementary tool for in situ characterization of thin film growth by ALD.     

Fischer-Tropsch synthesis on anchored Co/Nb2O5/Al2O3 catalysts: the nature of the surface and the effect on chain growth

A series of Co/x%Nb2O5/Al2O3 catalysts were prepared by anchoring niobia on an Al2O3 support at different niobia concentrations. Characterization of the structure and nature of surface active sites was attempted in order to correlate the CO hydrogenation activity of these systems with those of the Co/Al2O3 and Co/Nb2O5 catalysts. The effect of the reduction temperature on the CO hydrogenation activity and selectivity was studied, showing that interaction of cobalt and niobia surface species favored the selectivity for hydrocarbon chain growth. However, this effect is less pronounced on the niobia-promoted Co/Al2O3 compared to Co/Nb2O5 catalysts. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS) results on Co/x%Nb2O5/Al2O3 showed prevailing amounts of Co2+ and Co3+ after calcination and reduction at 573 K, while, after reduction at 773 K, besides metallic cobalt, the Co2+ species still remains in contact with alumina, even for higher niobia loading. It seems that during this process formation and destruction of new interfaces involving Co0-NbOx sites takes place. Results suggest that Co0, Co0-Co2+, and Co0-NbOx are the active sites at the surface. The relative abundance of Co2+ species affects greatly the performance of the catalysts. DRIFTS and selectivity results suggest that these sites might be responsible for the reaction chain growth and therefore for the drastic change in the selectivity of CH4 and C5+ hydrocarbons mainly on the Co/Nb2O5 catalyst. DRIFTS results on Co/Nb2O5/Al2O3 showed the formation of -C=C- and -CH3- besides CHxO species. With increasing reduction temperature, the -C=C- species disappear while -CH3- fragments increased markedly, suggesting the formation of increasing amounts of hydrocarbons with higher chain length.     

Role of water in the atomic layer deposition of TiO(2) on SiO(2)

Atomic layer deposition (ALD) of TiO(2) on SiO(2) powder using sequential addition of TiCl(4) and H(2)O vapors has been investigated by infrared spectroscopy. In the first cycle, TiCl(4) reacts monofunctionally or bifunctionally with surface silanols forming (Si-O-)(n)Ti-Cl(4)(-)(n) (n = 1, 2) species. Subsequent addition of water vapor leads to the hydrolysis of the (Si-O-)(n)Ti-Cl(4)(-)(n) to form a Ti-O-Ti network, and at the same time, some cleavage of Si-O-Ti bonds occurs, regenerating Si-OH in the process. It is shown that the species formed on the surface in the first TiCl(4) dose are temperature dependent. However, after addition of H(2)O vapor, the amount of TiO(2) deposited in the first complete cycle is independent of reaction temperature. In the second and above cycles, the amount of TiO(2) deposited as a function of ALD cycles strongly correlates with the amount of water on the surface. This, in turn, led to a temperature dependence of the growth rate of the TiO(2) per cycle.     

铂基催化剂用于柴油烃氧化

The catalytic performance of Pt-based catalysts for the total oxidation of hydrocarbons was investigated.The activity of supported Pt catalysts(Pt/Al2O3,Pt/ZrO2,Pt/TiO2,and Pt/H-ZSM-5)depends on the metal oxide support.Pt/Al2O3 showed the highest catalytic activity when the catalysts were aged at 750°C for 50 h in air.The activity of Pt/Al2O3 was dependent on the valence state of the Pt surface.Pt/Al2O3 with the Pt surface in the metallic state was more active than with the surface in the cationic state.The surface density of acid and basic sites on the Al2O3 support controlled the valence state of the Pt surface and stability of the Pt particles in the highly dispersed state,respectively.     

The importance of dye chemistry and TiCl(4) surface treatment in the behavior of Al(2)O(3) recombination barrier layers deposited by atomic layer deposition in solid-state dye-sensitized solar cells

Atomic layer deposition (ALD) was used to fabricate Al(2)O(3) recombination barriers in solid-state dye-sensitized solar cells (ss-DSSCs) employing an organic hole transport material (HTM) for the first time. Al(2)O(3) recombination barriers of varying thickness were incorporated into efficient ss-DSSCs utilizing the Z907 dye adsorbed onto a 2 μm-thick nanoporous TiO(2) active layer and the HTM spiro-OMeTAD. The impact of Al(2)O(3) barriers was also studied in devices employing different dyes, with increased active layer thicknesses, and with substrates that did not undergo the TiCl(4) surface treatment. In all instances, electron lifetimes (as determined by transient photovoltage measurements) increased and dark current was suppressed after Al(2)O(3) deposition. However, only when the TiCl(4) treatment was eliminated did device efficiency increase; in all other instances efficiency decreased due to a drop in short-circuit current. These results are attributed in the former case to the similar effects of Al(2)O(3) ALD and the TiCl(4) surface treatment whereas the insulating properties of Al(2)O(3) hinder charge injection and lead to current loss in TiCl(4)-treated devices. The impact of Al(2)O(3) barrier layers was unaffected by doubling the active layer thickness or using an alternative ruthenium dye, but a metal-free donor-π-acceptor dye exhibited a much smaller decrease in current due to its higher excited state energy. We develop a model employing prior research on Al(2)O(3) growth and dye kinetics that successfully predicts the reduction in device current as a function of ALD cycles and is extendable to different dye-barrier systems.     

New functionalized flexible Al-MIL-53-X (X = -Cl, -Br, -CH3, -NO2, -(OH)2) solids: syntheses, characterization, sorption, and breathing behavior

Five new flexible functionalized aluminum hydroxo terephthalates [Al(OH)(BDC-X)]·n(guests) (BDC = 1,4-benzene-dicarboxylate; X = -Cl, 1-Cl; -Br, 2-Br; -CH(3), 3-CH(3); -NO(2), 4-NO(2); -(OH)(2), 5-OH(2)) were synthesized under solvothermal conditions. The as synthesized (Al-MIL-53-X-AS) as well as the activated compounds were characterized by X-ray powder diffraction (XRPD), IR spectroscopy, thermogravimetric (TG), and elemental analysis. Activation, that is, removal of unreacted H(2)BDC-X molecules and/or occluded solvent molecules, followed by hydration in air at room temperature, led to the narrow pore (NP) form of the title compounds [Al(OH)(BDC-X)]·n(H(2)O) (Al-MIL-53-X). Thermogravimetric analysis (TGA) and temperature-dependent XRPD (TDXRPD) experiments performed on the NP-form of the compounds indicate high thermal stability in the range 325-500 °C. As verified by N(2), CO(2), or H(2)O sorption measurements, most of the thermally activated compounds exhibit significant microporosity. Similar to pristine Al-MIL-53, the present compounds retain their structural flexibility depending on the nature of guest molecules and temperature, as verified by cell parameter determination from XRPD data. The breathing behavior of the functionalized frameworks upon dehydration-rehydration, investigated by temperature and time-dependent XRPD measurements, differs significantly compared to parent Al-MIL-53.     

Fe-Mn/Al2O3催化剂低温 NH3选择性催化还原 NO的性能

本文制备了一系列 Fe-Mn/Al2O3催化剂,并在固定床上考察了其 NH3低温选择性催化还原 NO的性能.首先考察了不同 Fe负载量制备的催化剂的脱硝性能,优选出最佳的 Fe负载量;在此基础上,研究了 Mn负载量对催化剂脱硝效率的影响;最后,对优选催化剂的抗 H2O和抗 SO2性能进行了实验研究;同时,对催化剂由于 SO2所造成的失活机制进行了考察.采用 N2吸附-脱附、X射线衍射、透射电镜、能量弥散 X射线谱、程序升温还原、程序升温脱附、X射线光电子能谱、热重和傅里叶变换红外光谱等方法对催化剂进行了表征.结果表明,最佳的 Fe和 Mn负载量均为8%,所制的8Fe-8Mn/Al2O3催化剂在150°C的脱硝效率可达近99%;同时,在整个低温测试区间(90–210°C)的脱硝效率均超过了92.6%. Fe在催化剂表面主要以 Fe3+形态存在,而 Mn主要包括 Mn4+和 Mn3+; Mn的添加提高了 Fe在催化剂表面的积累,促进了催化剂比表面积增大和活性物种分散,改善了催化剂氧化还原性能和对 NH3的吸附能力.催化剂的高活性主要是由于其具有较大的比表面积、高度分散的活性物种、增加的还原特性和表面酸性、较低的结合能、较高的 Mn4+/Mn3+和增强的表面吸附氧.此外,8Fe-8Mn/Al2O3的催化性能受 H2O和 SO2影响较小,抗 H2O和 SO2能力较强.同时,反应温度对催化剂的抗硫性有重要影响,在较低的反应温度下,催化剂抗硫性更好; SO2造成催化剂活性降低主要是由于催化剂表面硫酸盐物种的生成.一方面,表面硫酸铵盐的生成造成催化剂孔道堵塞和比表面积降低,减少了反应中的气固接触从而导致活性降低;另一方面,催化剂表面的活性物种被硫酸化,造成反应中的有效活性位减少,从而降低了催化剂活性.     

Localized surface plasmon resonance nanosensor: a high-resolution distance-dependence study using atomic layer deposition

Atomic layer deposition (ALD) is used to deposit 1-600 monolayers of Al(2)O(3) on Ag nanotriangles fabricated by nanosphere lithography (NSL). Each monolayer of Al(2)O(3) has a thickness of 1.1 A. It is demonstrated that the localized surface plasmon resonance (LSPR) nanosensor can detect Al(2)O(3) film growth with atomic spatial resolution normal to the nanoparticle surface. This is approximately 10 times greater spatial resolution than that in our previous long-range distance-dependence study using multilayer self-assembled monolayer shells. The use of ALD enables the study of both the long- and short-range distance dependence of the LSPR nanosensor in a single unified experiment. Ag nanoparticles with fixed in-plane widths and decreasing heights yield larger sensing distances. X-ray photoelectron spectroscopy, variable angle spectroscopic ellipsometry, and quartz crystal microbalance measurements are used to study the growth mechanism. It is proposed that the growth of Al(2)O(3) is initiated by the decomposition of trimethylaluminum on Ag. Semiquantitative theoretical calculations were compared with the experimental results and yield excellent agreement.     

Synthesis, thermal and spectral characterization of nanosized Ni(x)Mg(1-x)Al2O4 powders as new ceramic pigments via combustion route using 3-methylpyrozole-5-one as fuel

New Ni(x)Mg(1-x)Al(2)O(4) nanosized in different composition (0.1≤x≤0.8) powders have been synthesized successively for first time by using low temperature combustion reaction (LTCR) of corresponding metal chlorides, carbonates and nitrates as salts with 3-methylpyrozole-5-one (3MP5O) as fuel at 300°C in open air furnace. Magnesium aluminate spinel (MgAl(2)O(4)) was used as crystalline host network for the synthesis of nickel-based nano ceramic pigments. The structure of prepared samples was characterized by using different techniques such as thermal analysis (TG-DTG/DTA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). UV/Visible and Diffuse reflectance spectroscopy (DRS) using CIE-L*a*b* parameters methods have been used for color measurements. The obtained results reveal that Ni(x)Mg(1-x)Al(2)O(4) powder of samples is formed in the single crystalline and pure phase with average particle size of 6.35-33.11 nm in the temperature range 500-1200°C. The density, particle size, shape and color are determined for all prepared samples with different calcination time and temperature.     

Influence of precursors chemistry on ALD growth of cobalt-molybdenum oxide films

Cobalt molybdenum compounds are important catalytic materials in many processes, e.g. in splitting of ammonia to form CO free hydrogen fuel. We here report on deposition of such cobalt molybdenum oxides by atomic layer deposition (ALD) using different types of metal precursors CoCp(2) (Cp = cyclopentadienyl), Co(thd)(2) (Hthd = 2,2,6,6-tetramethylheptan-3,5-dione), Mo(CO)(6) and oxygen precursors O(3), H(2)O, and (O(3) + H(2)O). The growth dynamics have been investigated using quartz crystal microbalance (QCM) methods. It is evident that mixing of the different precursor chemistries affect the growth patterns. When water is introduced to the reactions, a surface controlled mechanism takes place which guides the deposited stoichiometry towards the CoMoO(4) phase over a wide range of cobalt rich pulsed compositions. This is a rare example of how surface chemistry can control stoichiometry of depositions in ALD. The deposited films have been investigated by X-ray diffraction, Raman spectroscopy and atomic force microscopy. The catalytic activity of selected films have been characterized by temperature programmed ammonia decomposition, proving the films to be catalytically active and lowering the decomposition temperature by some 200 °C.     

Nanometer-thick conformal pore sealing of self-assembled mesoporous silica by plasma-assisted atomic layer deposition

On a porous substrate, regular atomic layer deposition (ALD) not only takes place on top of the substrate but also penetrates into the internal porosity. Here we report a plasma-assisted process in which the ALD precursors are chosen to be nonreactive unless triggered by plasma, so that ALD can be spatially defined by the supply of plasma irradiation. Since plasma cannot penetrate within the internal porosity, ALD has been successfully confined to the immediate surface. This not only gives a possible solution for sealing of porous low dielectric constant films with a conformal layer of nm-scale thickness but also enables us to progressively reduce the pore size of mesoporous materials in a sub-A/cycle fashion for membrane formation.     

Difference in the dynamic properties of chiral and racemic crystals of serine studied by Raman spectroscopy at 3-295 K

Single-crystal polarized Raman spectra (60-4000 cm(-1) at 3 < or = T < or = 295 K) were measured for chiral L- and racemic DL-serine, alpha-amino-beta-hydroxypropionic acid, (NH3)+CH(CH2OH)(COO)-. The Raman spectra of dl-serine do not show any striking changes with temperature or on storage. In contrast to that, the dynamical properties of L-serine change at about 140 K. These changes can be interpreted as the reorientation of the side chain -CH2OH fragments of the zwitterions with respect to the backbone C-C bonds, resulting in the positional disorder of the O-H...O intermolecular H-bonds. The redistribution in the intensities of the Raman spectra of the crystals of L-serine stored for a long time (about a year) indicates the changes in the orientation of the molecular fragments in the direction normal to the axes of the head-to-tail chains. The difference in the thermodynamic functions of L- and DL-serine reported previously [Drebushchak, V. A.; Kovalevskaya, Yu. A.; Paukov, I. E.; Boldyreva, E. V. J. Therm. Anal. Calorim. 2007, 89 (2), 649-654] is explained by the difference in the spectra of external vibrations of the crystals.     

Studies on the Synthesis, Properties andPreparation Methods of Zeolite ZK-4

IntroductionIn 1961 Kerr et al. LI] first synthesized a new zeolite designated ZK-4 whose crystal structure is similar to that of zeolite A, but whose chemical composition differs significantly fromthat of zeolite A. Like zeolite A, ZK-4 contains 24 tetrahedra in a cubic unit cell. However,zeolite ZK--4 has a ratio of silicon to aluminium greater than 1. 0. This increases the siliconcontent of the new zeolite, resulting in smaller unit cell parameters than those of zeolite A.Because the …     

Glow discharge deposition of silicon dioxide and aluminum oxide films: A kinetic model of the surface processes

Silicon oxide films have been deposited in a RF discharge plasma using hexamethyl-disiloxane (HMDSO) and Ar/O₂ or N₂O. Also, aluminum oxide layers have been deposited using trimethylaluminum (TMA) and N₂O or CO₂. The influence of the nature and the proportion q( the oxidizing gases and file suhstrate temperature effect have been studied. As far as the films obtained with HMDSO and TMA tire concerned, the most important experimental finding is the decrease of the deposition rate with increasing substrate temperature. FTIR, ESCA, and refractive index measurements show that the decrease of the deposition rate correlates with a nearly stoichiometric film. Low negative apparent activation energies are deduced from Arrhenius plots and are representative of deposition rates controlled hr fire adsorption of radical and surface di fusivities. A kinetic rnodel shows that the rate-limiting step is the adsorption of HMDSO or TMA radicals at low temperatures while for temperatures above 250°C the oxidation reactions control the deposition rate.     

Pt/Co3O4/3DOM Al2O3：甲苯燃烧的高效催化剂

与硫氧化物、氮氧化物、一氧化碳以及悬浮颗粒一样,大部分挥发性有机物(VOCs)污染大气环境.控制 VOCs排放有多种方法,其中催化氧化法是一种有效技术,关键在于获得高效催化剂.
　　近年来,负载过渡金属和贵金属催化剂因具有比单纯负载贵金属和单纯负载过渡金属氧化物更好的催化性能而备受关注.在负载贵金属催化剂中,高比表面积载体负载 Pt, Pd或 Rh催化剂得到广泛而深入的研究,尽管这些催化剂成本较高,但是其对 VOCs氧化反应显示了很高的低温催化活性.众所周知,催化活性取决于贵金属和 VOCs的种类,不同负载贵金属催化剂对特定反应会表现出不同的催化活性.负载 Pt催化剂对长链碳氢化合物和芳香族化合物氧化反应表现出更高的活性.相对于负载贵金属催化剂,负载过渡金属氧化物催化剂不仅具有良好的氧化活性,而且价格低廉.迄今已发现许多过渡金属氧化物(如 Co3O4, Cr2O3和 MnO2等)对典型 VOCs氧化反应具有催化活性,其中 Co3O4的催化活性尤为突出.研究表明, Co3O4的性质和分散度是决定其性能的关键因素,制备方法、载体性质和过渡金属氧化物负载量对 Co3O4的物化性质具有重要影响,而且在负载 Pt催化剂中添加金属氧化物能改善其催化性能.尽管多孔氧化铝是一种常用的载体材料,但目前尚无文献报道三维有序大孔-介孔氧化铝负载 Co3O4和 Pt纳米粒子催化剂的制备及其对甲苯氧化反应的催化性能.
　　本文采用聚甲基丙烯酸甲酯微球胶晶模板法、等体积浸渍法和聚乙烯醇保护的硼氢化钠还原法制备了三维有序大孔-介孔(3DOM Al2O3)负载 Co3O4和 Pt (xPt/yCo3O4/3DOM Al2O3, Pt的质量分数(x%)为0-1.4%, Co3O4的质量分数(y%)为0-9.2%)纳米催化剂.通过电感耦合等离子体原子发射光谱、X射线衍射、氮气吸附-脱附、扫描电子显微镜、透射电子显微镜、选区电子衍射、X射线光电子能谱及氢气程序升温还原等技术表征了催化剂的物化性质,利用固定床微型石英反应器评价了催化剂对甲苯氧化反应的催化活性.结果表明,xPt/yCo3O4/3DOMAl2O3催化剂具有多级孔结构(大孔孔径为180–200 nm,介孔孔径为4–6 nm),比表面积为94?102 m2/g.粒径为18.3 nm的 Co3O4纳米粒子和粒径为2.3?2.5 nm的 Pt纳米粒子均匀分散在3DOM Al2O3表面.在xPt/yCo3O4/3DOM Al2O3催化剂中,1.3Pt/8.9Co3O4/3DOM Al2O3拥有最高的 Oads浓度、最好的低温还原性和最高的甲苯氧化反应催化活性(当空速为20000mL g–1 h–1时,甲苯转化率达90%的反应温度为160oC).基于催化剂的活性数据和结构表征,我们认为,1.3Pt/8.9Co3O4/3DOM Al2O3优异的催化性能与其高分散的 Pt纳米粒子、高的 Oads浓度、好的低温还原性、Pt和 Co3O4纳米粒子间的强相互作用以及多级孔结构相关.     

Microwave and UV excitation spectra of 4-fluorobenzyl alcohol at high resolution. S0 and S1 structures and tunneling motions along the low frequency -CH2OH torsional coordinate in both electronic states

Rotationally resolved electronic spectra of several low frequency vibrational bands that appear in the S(1) ← S(0) transition of 4-fluorobenzyl alcohol (4FBA) in the collision-free environment of a molecular beam have been observed and assigned. Each transition is split into two or more components by the tunneling motion of the attached -CH(2)OH group. A similar splitting is observed in the microwave spectrum of 4FBA. Analyses of these data show that 4FBA has a gauche structure in both electronic states, but that the ground state C(1)C(2)-C(7)O dihedral angle of ～60° changes by ～30° when the photon is absorbed. The barriers to the torsional motion of the attached -CH(2)OH group are also quite different in the two electronic states; V(2) ～ 300 cm(-1) high and ～60° wide in the S(0) state, and V(2) ～ 300 cm(-1) high and ～120° wide (or V(2) ～ 1200 cm(-1) high and ～60° wide) in the S(1) state. Possible reasons for these behaviors are discussed.