Raman and IR studies of surface metal oxide species on oxide supports: Supported metal oxide catalysts

Raman and infrared spectroscopy provide complementary information about the nature of the surface metal oxide species present in supported metal oxide catalysts. This paper reviews the type of fundamental information that is typically obtained in Raman and IR characterization studies of supported metal oxide catalysts. The molecular structures of the surface metal oxide species are reflected in the terminal M=O and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports is determined by directly monitoring the specific surface hydroxyls of the support that are being titrated. The surface coverage of the surface metal oxide species on the oxide supports can be quantitatively obtained since at monolayer coverage all the reactive surface hydroxyls are titrated and additional metal oxide results in the formation of crystalline metal oxide particles. The nature of surface Lewis and Brønsted acid sites present in supported metal oxide catalysts are determined by adsorbing basic probe molecules like pyridine. Information about the behavior of the surface metal oxide species during catalytic reactions are provided by in situ characterization studies. Such fundamental information is critical for the development of molecular structure-reactivity relationships for supported metal oxide catalysts. This paper will be limited to supported metal oxide catalysts containing group V-VII transition metal oxides (e.g., V, Nb, Cr, Mo, W and Re) on several different oxide supports (alumina, titania, zirconia, niobia and silica).     

Ultrasonication-assisted ultrafast reduction of graphene oxide by zinc powder at room temperature

A green method is reported to effectively and rapidly reduce graphene oxide to graphene with zinc powder at room temperature. The reduction is carried out by mixing graphene oxide and zinc powder in solution under ultrasonication. The reduction is complete within 1 min. The weight of the Zn powder should be at least as twice as that of graphene oxide to complete the reduction. The reduction of graphene oxide is confirmed by FTIR, UV–Vis absorption spectroscopy and Raman spectroscopy. The carbon/oxygen atomic ratio has increased from 2.58 to 33.5 after the reduction as determined by X-ray photoelectron spectroscopy. The reduced graphene oxide can have a conductivity of 15,000 S/m. It also has good thermal stability with the weight loss at 590 °C in air. The reduced graphene oxide can be readily re-dispersed into solutions of various surfactants.     

X 射线荧光光谱法测定砂岩中SiO2、Al2O3、CaO、MgO 含量

确定了用 X 射线荧光光谱法测定砂岩中 SiO2、Al2O3、CaO、MgO 的含量的最佳测定条件,该方法简单、分析速度快,SiO2、Al2O3、CaO、MgO 的相对标准偏差分别为0.22%、1.9%、5.3%、6.1%,结果稳定可靠.经大量试验证明,采用此法测定,操作方便,准确度高,结果令人满意.     

Al_2O_3基催化剂中TiO_2的分析

介绍了一种分析Al_2O_3基催化剂中Ti含量的方法。采用浓硫酸并加热溶解催化剂试样,控制待测溶液中硫酸浓度为2mol/L,加入5mL质量分数3%的过氧化氢作为显色剂,在分光光度计上进行比色,可快速测定Al_2O_3基催化剂中Ti的含量。试样测定的相对标准偏差小于或等于1.13%。     

球形氧化铝制备过程中影响因素的研究

介绍了球形氧化铝的各种制备工艺及成形方法，并以油柱成形法制备球形氧化铝。利用低温液氮吸附仪、压汞仪以及智能强度测定仪对其物化性质进行了测定，重点考察了不同铝源合成的水合氧化铝、加料方式、扩孔剂和胶溶剂用量对球形氧化铝性质的影响。实验结果表明，制备水合氧化铝的铝源是影响球形氧化铝的重要因素；并流加料方式能制得大孔容、低表观密度、高强度的球形氧化铝；球形氧化铝的制备过程中，要制得适合于油柱成形的铝溶胶，胶溶剂加入量有最佳的用量范围，胶溶剂用量愈大，球性氧化铝的强度、比表面、孔容愈大，而孔径却随之变小；活性炭粉能有效地提高球形氧化铝的压汞孔容。     

新型纳米氧化钨的近红外吸收性能

采用化学沉淀法制备纳米氧化钨粉体,并用氢氮混合气对其进行还原处理,分析了还原处理温度对氧化钨化学组成的影响,用 X 射线粉末衍射仪表征了纳米氧化钨粒子的晶相与化学组成,采用扫描电子显微镜观察了该粒子还原处理前后的晶相形貌,并测定了由该纳米颗粒还原前后制得的胶状液体从可见光到近红外波长范围内的吸收光谱和透过光谱。研究表明：还原后的氧化钨纳米粒子对 1400～1600nm 和 1900～2200nm 波段的近红外光具有显著的吸收增强效应,同时对可见光具有很高的透过性,这种具有特殊光学吸收特性的纳米氧化钨可望在新型太阳能热屏蔽器件的设计中得到应用。     

The development of cerium oxide coatings from cryolite melts. A self-forming anode for aluminum electrowinning

The anodic deposition of cerium oxide from cryolite melts onto tin oxide substrates was investigated. Such a coated structure offers promise as an oxygen-evolving anode in Hall-Heroult cells. The development and dimensional stability of the coating is established by the equilibrium between the bath components and the cerium oxide. The coating thickness and morphology is shown to be dependent on the initial cerium oxide bath concentration and, to a lesser extent, on current density. The presence of the cerium oxide coating greatly diminishes dissolution of the anode substrate and increases the purity of the electrowon aluminum. The protection afforded by the coating is achieved by reducing the exposed substrate surface area.     

Estimation of nitric oxide emissions from an internal combustion engine

The analysis of nitric oxide, the principal nitrogen oxide in raw exhaust gas, is described by two different techniques. Concordance of analytical determinations using the Saltzman colorimetric solution method with the gas phase chemiluminescence method is demonstrated. By dilution of exhaust gas from an internal combustion engine with nitrogen it is shown that gas samples can be stored for periods of at least 30 min without significant change in sample composition with respect to nitric oxide. This procedure enables reliable estimations of nitric oxide in exhaust gas contained in a sealed transportable vessel to be performed at sites remote from the sample point, without introducing errors due to loss of nitric oxide by chemical reaction in the time between sampling and analysis.     

Emission of nitrous oxide from soils used for agriculture

Nitrous oxide is emitted into the atmosphere as a result of biomass burning, and biological processes in soils. Biomass burning is not only an instantaneous source of nitrous oxide, but it results in a longer term enhancement of the biogenic production of this gas. Measurements of nitrous oxide emissions from soils before and after a controlled burn showed that significantly more nitrous oxide was exhaled after the burn. The current belief is that 90% of the emissions come from soils. Nitrous oxide is formed in soils during the microbiological processes nitrification and denitrification. Because nitrous oxide is a gas it can escape from soil during these transformations. Nitrous oxide production is controlled by temperature, pH, water holding capacity of the soil, irrigation practices, fertilizer rate, tillage practice, soil type, oxygen concentration, availability of carbon, vegetation, land use practices and use of chemicals. Nitrous oxide emissions from agricultural soils are increased by the addition of fertilizer nitrogen and by the growth of legumes to fix atmospheric nitrogen. A recent analysis suggests that emissions of nitrous oxide from fertilized soils are not related to the type of fertilizer nitrogen applied and emissions can be calculated from the amount of nitrogen applied. Legumes also contribute to nitrous oxide emission in a number of ways, viz. atmospheric nitrogen fixed by legumes can be nitrified and denitrified in the same way as fertilizer nitrogen, thus providing a source of nitrous oxide, and symbiotically living Rhizobia in root nodules are able to denitrify and produce nitrous oxide. Conversion of tropical forests to crop production and pasture has a significant effect on the emission of nitrous oxide. Emissions of nitrous oxide increased by about a factor of two when a forest in central Brazil was clear cut, and pasture soils in the same area produced three times as much nitrous oxide as adjacent forest soils. Studies on temperate and tropical rice fields show that less than 0.1% of the applied nitrogen is emitted as nitrous oxide if the soils are flooded for a number of days before fertilizer application. However, if mineral nitrogen is present in the soil before flooding it will serve as a source of nitrous oxide during wetting and drying cycles before permanent flooding. Thus dry seeded rice can be a source of considerable nitrous oxide. There are also indirect contributions to nitrous oxide emission through volatilization of ammonia and emission of nitric oxides into the atmosphere, and their redistribution over the landscape through wet and dry deposition. In general nitrous oxide emissions can be decreased by management practices which optimize the crop's natural ability to compete with processes whereby plant available nitrogen is lost from the soil-plant system. If these options were implemented they would also result in increased productivity and reduced inputs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetics of the electrolytic coloring process on anodized aluminum

The kinetics of tin electrodeposition during the electrolytic coloring of porous anodic oxide films on aluminum is studied as a function of the oxide properties, e.g., the thickness of the porous oxide layer, and the surface resistance offered by the barrier oxide layer. While the thickness of the porous oxide layer is controlled by the anodization time, the surface resistance is controlled by the anodization voltage, and the anodization bath temperature. Steady-state polarization measurements are employed to characterize the dependence of the coloring kinetics on the oxide properties. Measurements indicate that the kinetics of the electrolytic coloring process can be accelerated by: (i) reducing the surface resistance of the oxide film (primarily offered by the barrier oxide layer) by growing the oxide at a lower anodization voltage, and/or a higher bath temperature, or (ii) growing a thinner porous oxide layer by decreasing the anodization time. The electrochemical measurements are supported by gravimetric analysis of electrolytically colored alumina samples (using calibrated wavelength-dispersive X-ray fluorescence spectroscopy), and by optical spectrophotometry.     

Concerning oxygen anions in a nitrate melt

Previous electrochemical measurements of the equilibrium constants for the oxidation of oxide ions by nitrate melts and associated equilibria are shown to be supported by other recent non-electrochemical measurements and by thermodynamic calculations. However, the hypothesis that the oxide ion is stabilized by nitrate anions (to form pyro- or orthonitrate anions) is shown to be inadequate to explain the experimental electrochemical results obtained by many workers.The alternative hypothesis of oxide ion stabilization by silica not only explains the existing measurements but allows consistent equilibrium constants to be calculated from existing data.The reaction between carbonate and powdered silica was shown to be rapid and to lead to a complex silicate but reaction with glass was found to be much slower. Similar differences in reactivity were observed with solutions of sodium peroxide. This kinetic stability of concentrated oxide, peroxide and hydroxide solutions in nitrate melts is thought to explain a number of other hitherto conflicting results.     

A mechanism theory of dissolution profile of oxide particles in oxide melt

The shape origin and variation of oxide dissolution profile in the oxide melt is for the first time explained with a mechanism of diffusion-distance-controlled dissolution (DDD). A novel analytical model is derived to present this theory. The profile shape is governed by the diffusion distance of the dissolved components in the oxide melt. The viscosity gradient at the boundary of the diffusion region provides the driving force for the profile variation. Both temperature and initial viscosity of oxide melt are the key factors determining the oxide dissolution kinetics. This theory can be applied to describe diffusion-limited particle dissolution in a general system.     

乙醇溶剂中硝酸银与氢氧化钠的反应机理

在乙醇溶剂中制备纳米Ag2O时,发现有纳米Ag2O和纳米Ag2种产物,进而通过XRD对其反应机理进行了研究。实验结果和理论分析表明,溶剂对制备纳米氧化银有很大影响,在乙醇溶剂中不能制备出纯的纳米氧化银;其反应机理为该反应首先是银离子与氢氧根离子反应生成氧化银沉淀,氧化银在碱性条件下将溶剂乙醇氧化为乙醛,而自身被还原为单质银;生成的乙醛又将银离子和氧化银还原为单质银,从而导致产物既有纳米氧化银又有纳米银;其中碱性介质是氧化银将乙醇氧化为乙醛的催化剂。     

Second Harmonic Generation studies of the oxidation of metal electrodes: Compact and hydrous oxide growth at gold electrodes in acid solutions

The oxidation of gold electrodes in aqueous media has been examined using Second Harmonic Generation (SHG). Initial growth of the compact or α oxide causes a substantial drop in SH generation even when only partial coverage of oxide is attained and this is suggested to be due to the effect of the development of the oxide on a surface plasmon derived from d-electrons in gold, the involvement of these electrons in oxide formation meaning that the surface plasmon can no longer propagate. When thicker hydrous (or β) oxides are grown on top of the α oxide by holding at constant potential, the subsequent reduction of the oxide leads to unusual narrow peaks (dips) in the SHG response which occur before any significant reduction charge is passed. As the amount of hydrous oxide increases, the initial single narrow SHG peak changes to a pair of peaks and these then merge into one broad peak. The SHG peaks are suggested to be related to an order-disorder transition at the interface between α and β oxides, or perhaps due to the presence of surface traps. Second Harmonic Generation is shown again to be a sensitive and informative technique Having sub-monolayer sensitivity for α oxide growth and offering insight into the reduction process of multilayer oxides.     

The formation of a peroxoantimonate thin film coating on graphene oxide (GO) and the influence of the GO on its transformation to antimony oxides and elemental antimony

The ultrathin peroxoantimonate coating of graphene oxide from hydrogen peroxide-rich solutions of hydroxoantimonate is demonstrated. An amorphous 1–2 nm Sb (V) oxide film is formed and can be further crystallized by exposure to an electron beam to give a 2–5 nm thick supported Sb₆O₁₃ particulate coating. Heat treatment of the peroxoantimonate yielded different crystalline oxides, whereas in the presence of the graphene support only trigonal Sb (0) was produced by heat treatment in vacuum or an argon atmosphere. The graphene oxide support is essential for the formation of the Sb (0) phase and even in air a substantial elemental antimony was obtained. Whereas heat treatment of uncoated graphene oxide in an inert atmosphere produces reduced graphene oxide, the antimony oxide coated graphene oxide is not reduced by the heat treatment. Only after the supported antimony oxide is reduced to give the trigonal Sb (0) phase the graphene oxide was reduced by the heat treatment. The phases before and after the different heat treatments are characterized by electron and X-ray diffraction, thermal analysis, XPS studies, electron microscopy and wet chemistry.     

The synthesis of barium hexaferrite from iron oxide and barium carbonate: II. The role of iron oxide texture

The texture of several samples of laboratory-prepared and commercial iron oxide and their reactivity with barium carbonate (BaCO₃.6Fe₂O₃) has been examined. The first stage of the reaction involves decarbonation with the formation of monoferrite and dynamic thermogravimetry was used to assess mix reactivity. While some of the variation in the behaviour of iron oxide powders could be appreciated from an examination of their texture by scanning electron microscopy and porosity determination, prediction of their reactivity was not possible. In fact the reactivity of the mix can best be considered to give an indication of the efficiency of mixing of the finer iron oxide particles with the barium carbonate. In the subsequent formation of barium hexaferrite the coarse end of the iron oxide particle size range is of primary importance since it controls the rate of completion of the reaction. The larger aggregates in an iron oxide sample can readily be detected by scanning electron microscopy but conclusions regarding reactivity may be erroneous if this coarse material is dispersed during mixing. It was shown by scanning electron microscopy that the least reactive iron oxide sample examined contained aggregates which survived the mixing process employed.     

The anodic oxide film on iron in neutral solution

The composition of the anodic passive oxide film on iron in neutral solution has been investigated by cathodic reduction, chemical analysis and ellipsometry. The cathodic reduction using a borate solution of pH 6·35 containing arsenic trioxide as inhibitor estimates iron in the film to be all iron (III), indicating that no magnetite layer is present. Oxygen in the film is estimated from the ellipsometric thickness to be in excess of the stoichiometric ferric oxide, suggesting the presence of bound water. The average composition is represented as Fe₂O₃.0·4H₂O, in which hydrogen may be replaced partly with iron-ion vacancy. The anodic oxide film is composed of an inner anhydrous ferric oxide layer, which thickens with the potential and an outer layer of hydrous ferric oxide whose thickness depends on the condition of passivation and environment.     

Cu基ZnO薄膜紫外光催化降解水中有机污染物

利用Cu基ZnO薄膜紫外光催化降解水体中的有机污染物是一项非常有前景的水处理技术,本文利用电化学沉积方法,在锌盐的水溶液中沉积制备Cu基ZnO薄膜,并以较难降解的偶氮类有色化合物甲基橙是为例,紫外光照射下,用制备好的Cu基ZnO薄膜降解水中甲基橙.结果表明有很好的催化降解效能.该技术还没有得到广泛应用,有待于进一步完善...     

纳米二氧化钛薄膜光催化剂的合成及特性

研究采用溶胶-凝胶技术以载玻片为基质制备了纳米TiO2薄膜,向溶胶中添加乙酰丙酮后改善了溶胶的稳定性及薄膜的牢固性。用扫描探针显微镜(DFM)、X射线衍射(XRD)、红外光谱(IR)及X射线光电子能谱(XPS)对薄膜进行了表征。结果表明:扫描探针显微镜(DFM)观察到薄膜中颗粒的粒径为20~40nm,X射线衍射(XRD)表明TiO2为锐钛型,用红外光谱(IR)表征了溶胶及粉末样品的物性并探讨了反应的机理,X射线光电子能谱(XPS)结果显示薄膜中除含有Ti、O元素外,还有少量从玻璃表面扩散至薄膜中的Na和Si元素。TiO2薄膜对光降解甲基橙水溶液具有很好的光催化性,通过掺SnO2、酸处理途径明显提高了其性能。     

A flame metal combustion method for production of nanoparticles

We propose a flame metal combustion method for continuously synthesizing metal oxide nanoparticles. Micro-sized metal powder precursors were injected into a hydrogen-oxygen flame through a newly designed feeder system in order to be completely converted into metal oxide nanoparticles with good crystallinity. There is no limitation in the selection of precursors including metal, metal chloride and metal organic powders to synthesize nanoparticles. Various oxides such as magnesia, iron oxides and zinc oxide were demonstrated to be successfully generated by using this method. The sizes of oxide nanoparticles were controlled by varying flame temperatures and residence times.