Vibrational spectral studies of solutions at elevated temperatures and pressures. X. Raman spectral study of aqueous cadmium bromide solutions at 25 and 200°C

The Raman spectra of cadmium bromide solutions with bromide to cadmium mole ratios varying from 1.0 to 9.74 were studied at 200°C. Factor analysis revealed that three complexes contributed to the spectra. From a comparison with previous results at 25°C these species were identified as CdBr₂, CdBr ₃ ^– , and CdBr ₄ ^2– cadmium existed as the tetrabromo complex, CdBr ₄ ^2– , at mole ratios greater than 5.99. A formation constant of 7±2 was determined for CdBr ₄ ^2– at 200°C. No evidence of Cd(H₂O) ₆ ²⁺ or CdBr⁺ was found, although electroneutrality dictates that one or both of these species must exist at low mole ratios.     

Correction of mass spectrometric isotope ratio measurements for isobaric isotopologues of O2, CO,CO2, N2O and SO2

Gas isotope ratio mass spectrometers usually measure ion current ratios of molecules, not atoms. Often several isotopologues contribute to an ion current at a particular mass‐to‐charge ratio (m/z). Therefore, corrections have to be applied to derive the desired isotope ratios. These corrections are usually formulated in terms of isotope ratios (R), but this does not reflect the practice of measuring the ion current ratios of the sample relative to those of a reference material. Correspondingly, the relative ion current ratio differences (expressed as δ values) are first converted into isotopologue ratios, then into isotope ratios and finally back into elemental δ values. Here, we present a reformulation of this data reduction procedure entirely in terms of δ values and the ‘absolute’ isotope ratios of the reference material. This also shows that not the absolute isotope ratios of the reference material themselves, but only product and ratio combinations of them, are required for the data reduction. These combinations can be and, for carbon and oxygen have been, measured by conventional isotope ratio mass spectrometers. The frequently implied use of absolute isotope ratios measured by specially calibrated instruments is actually unnecessary. Following related work on CO₂, we here derive data reduction equations for the species O₂, CO, N₂O and SO₂. We also suggest experiments to measure the required absolute ratio combinations for N₂O, SO₂ and O₂. As a prelude, we summarise historic and recent measurements of absolute isotope ratios in international isotope reference materials. Copyright © 2008 John Wiley & Sons, Ltd.     

The mercury-sensitized oxidation of carbon monoxide

The mercury-photosensitized oxidation of CO was studied at 275°C over a wide range of [O₂]/[CO] ratios in the absence and presence of the oxygen atom scavenger 2-trifluoromethylpropene (TMP) and at 25°C at low [O₂]/[CO] ratios in the presence of TMP. By following the quantum yield of CO₂ production, Φ {CO₂}, as a function of the [O₂]/[CO] ratio, the reactions of vibrationally excited CO (v υ 9) and electronically excited O₂, probably in the c¹Σ^?_u state, were studied. At low [O₂]/[CO] ratios the predominant reactions are of vibrationally excited CO (v υ 9). Relative rate constants for chemical reaction versus deactivation of CO (v υ 9) were obtained. At higher [O₂]/[CO] ratios, the principal reactions are of electronically excited O₂. Relative rate constants for chemical reactions and deactivation of this electronically excited O₂ with CO, O₂, and TMP were obtained. From the effect of total pressure on Φ {CO₂}, it is proposed that an intermediate CO₃ is formed in the reaction of electronically excited O₂ with CO.     

Enhancement of stereospecificity in isoprene polymerization with alkylaluminum–titanium chloride catalysts through use of carbon disulfide

The effect of CS₂ on isoprene polymerization with triisobutylaluminum-titanium tetrachloride catalysts was studied at Al/Ti ratios of optimum (0.9) and higher values. In the absence of CS₂, appreciable amounts of low molecular weight oils (“extractables”) were formed at the expense of cis-1,4-polyisoprene with higher than optimum Al/Ti ratios. Small amounts of CS₂ were found to prevent extractables formation and allow attainment of higher yields of cis-1,4-polyisoprene. The optimum CS₂/Ti chloride molar ratio (0.1) was independent of the Al/Ti ratio of the catalyst. Polymer microstructure and dilute solution viscosity were unaffected by CS₂. The results support the theory that the catalyst surfaces hold two types of active sites: p-sites, which initiate polymerization, and o-sites, which lead to oligomerization. CS₂ appears to enhance polymerization by coordinating selectively at the o-sites. The predominance of oligomerization at the higher Al/Ti ratios was attributed to a destruction of p-sites by excess trialkyl-aluminum.     

Raman spectral studies of aqueous zinc bromide solutions to 300°C at pressures of 9 MPa

A Raman spectral study of 14 solutions of varying bromide to zinc ratios was conducted up to 300°C and 9 MPa. The tetra-, tri-, di- as well as the mono-bromozinc complexes were identified. The signal from the ZnBr⁺ complex increased in intensity as temperature increased, for solutions of low bromide- to-zinc ratios. The ZnBr ₄ ^2– species was favored at higher Br/Zn ratios, and higher temperatures favored the formation of the species ZnBr₂ and ZnBr⁺ at the expense of ZnBr ₄ ^2– and ZnBr ₃ ^– . Although solvated water is probably present in these zinc-bromo complexes, we found no evidence of O–Zn vibrations other than for Zn(H₂O) ₆ ²⁺ . However, spectra of successive dilutions of solutions with high bromide to zinc ratios show a relative change in species populations thereby suggesting that water activity plays a decisive role in complex formation. For the first time trifluoromethanesulfonic acid (HTFMS) has been used as an internal standard in Raman spectroscopy. This permitted quantitative measurement of stepwise stability constants.     

Isotopomeric analysis of N2O dissolved in a river in the Tokyo metropolitan area

River water has been suggested as a potential source of nitrous oxide (N₂O), which is a greenhouse gas that is accumulating rapidly in the troposphere and which is a precursor to stratospheric NO_x that depletes ozone. Previous studies on freshwater N₂O sources have specifically examined estuaries where sedimentary N₂O production might be important and a few points near anthropogenic nitrogen sources such as agricultural or municipal wastewater areas. Here we present the first observation of a temporal and horizontal distribution of N₂O and its isotopomers between the midstream and estuary of an urban river. Surface water was supersaturated (100–6800%) with N₂O at all stations during the study period. The average or maximum saturation value was greater than described in most previous reports. High N₂O concentrations were observed near sewage plants and the unique signature of isotopomer ratios implied direct N₂O addition from the plants. The isotopomer ratios also suggested N₂O production/consumption at the sediment‐water interface. Fluxes and isotopomer ratios of N₂O, from the river to the atmosphere, estimated from our observations, indicated that the urban river is indeed a source of atmospheric N₂O and that its production could be distinguished from other natural or anthropogenic sources using isotopomer ratios. Copyright © 2009 John Wiley & Sons, Ltd.     

Characteristics of lime-silica fume mixtures

The hydration of two calcium hydroxide-silica fume mixtures was studied at 25°C. The mixtures were prepared at lime/silica molar ratios of 1.0 and 1.7. The free lime, free silica and chemically combined water contents were determined after various periods of hydration (0.5 h-90 days). Thus, the molar ratios CaO/SiO₂ and H₂O/SiO₂ molar in the calcium silicate hydrates (C-S-H) formed could be derived. The hydrates formed were identified by using differential thermal analysis. The mechanism of the hydration-gardening thermal analysis. The mechanism of the hydration-hardening reaction between lime and silica fumes was suggested. The changes in the molar ratios CaO/SiO₂ and H₂O/SiO₂ in the C-S-H formed with the time of hydration were found to follow the same trends as observed during the hydration course for the suggested mechanism.     

The formation of V-bearing ferrite by aerial oxidation of an aqueous suspension

Stoichiometric V-bearing ferrites, Fe₂VO₄Fe₃O₄ solid solutions, were formed by the aerial oxidation of aqueous suspensions at V⁴⁺/Fe_total molar ratios of 0.034 and 0.072 in the initial solutions, at pH 11.0 and 65°C. At V⁴⁺/Fe_total ratios of from 0.111 to 0.154 in the initial solution, the V-bearing ferrites formed were slightly further oxidized. At ratios above 0.20 in the initial solution, α-FeOOH was formed together with V-bearing ferrites having a higher V⁴⁺ content, and the ferrites were further oxidized in the course of the aerial oxidation and drying.     

系列硅铝比纳米薄层ZSM-5分子筛的合成和表征

以自制不对称双子季铵盐表面活性剂为模板, 在水热合成体系中控制合成系列硅铝比纳米薄层ZSM-5分子筛.采用X射线衍射(XRD)、N₂吸附-脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)和²⁷Al魔角旋转核磁共振(²⁷Al MAS-NMR)对合成的样品进行了表征. 详细研究了晶化温度、晶化时间、结构导向剂(SDA)用量、碱度等对合成的影响和纳米薄层ZSM-5分子筛的形成过程. 结果表明: 分子筛硅铝比越高, 结构导向剂用量越大, 所需的晶化时间越短; 晶化温度越高, 晶化时间越短; 且不同硅铝比纳米薄层ZSM-5分子筛的形貌规整度、比表面积和介孔/微孔孔容比例随着硅铝比而变化.     

Effect of O2/CH4 ratio on the optimal specific-energy-input (SEI) for oxidative reforming of biogas in a plasma-shade reactor

In a novel plasma-shade reactor for oxidative reforming of biogas (CH₄/CO₂ = 3/2), the effects of specific-energy-input (SEI) on CH₄ and CO₂ conversions and energy cost of syngas were investigated at O₂/CH₄ ratios ranged from 0.42 to 0.67. At each of O₂/CH₄ ratios, V-shape profiles of energy cost of syngas increasing with SEI were observed, reaching the lowest value at the optimal SEI (Opt-SEI). With the increase of O₂/CH₄ ratio, the Opt-SEI decreased significantly. Moreover, at the Opt-SEI, O₂ and CH₄ conversions and dry-basis concentration of syngas increased and energy cost of syngas decreased greatly with the increase of O₂/CH₄ ratio.     

Autothermal reforming of biogas over a monolithic catalyst

This study focused on measurement of the autothermal reforming of biogas over a Ni based monolithic catalyst. The effects of the steam/CH₄ (S/C) ratio, O₂/CH₄ (O₂/C) ratio and temperature were investigated. The CH₄ conversions were higher under all examined temperatures than the equilibrium conversion calculated using the blank outlet temperature, because the catalyst layer was heated by the exothermic catalytic partial oxidation reaction. The CH₄ conversion increased with increasing O₂/C ratio. Moreover, the CH₄ conversion was higher than the equilibrium conversion calculated using the blank outlet temperature for O₂/C>0.42 and reached about 100% at O₂/C=0.55. However, the hydrogen concentration decreased for O₂/C>0.45 because hydrogen was combusted to steam in the presence of excess oxygen. On the other hand, the hydrogen and CO₂ concentrations increased and the CO concentration decreased with increasing S/C ratio. As a result, it was found that the highest hydrogen concentrations and CH₄ conversions were attained at the O₂/C ratios of 0.45-0.55 and the S/C ratios of 1.5-2.5. Moreover, the H₂/CO ratio could also be controlled in the range from about 2 to 3.5 to give at least 90% CH₄ conversion, by regulating the O₂/C or S/C ratios.     

Optimizing the parameters of the steam-carbon dioxide conversion of methane by Gibbs energy minimization

The thermodynamic equilibrium for the steam-carbon dioxide conversion of methane was studied by Gibbs energy minimization. The degree of coke formation, the content of methane and carbon dioxide in the synthesis gas, and the synthesis gas H₂/CO ratio were plotted as functions of the molar ratios of CO₂/CH₄ and H₂O/CH₄ in the initial mixture at different temperatures and pressures. The regions of the optimum CH₄/CO₂/H₂O molar ratios for steam-carbon dioxide conversion were discovered, with no coke formation taking place in these regions. The optimized CH₄/CO₂/H₂O molar fractions characterized by the minimum content of methane and carbon dioxide in the synthesis gas were found for each region.     

Radical polymerizations of a silicone‐containing acrylic monomer in supercritical carbon dioxide

Radical homopolymerizations and copolymerizations of 3‐[tris(trimethylsilyloxy)silyl]propyl methacrylate (SiMA) in supercritical CO₂ were investigated. The homopolymer was obtained in CO₂ with a good yield. It was essentially insoluble in pure CO₂ at less than 500 bar at 65 °C but was soluble in a mixture of CO₂ and its monomer (10 w/v %) at 352 bar. The copolymerizations of SiMA with methyl methacrylate, 1,1‐dihydroperfluorooctyl methacrylate, and styrene with various monomer feed ratios were also examined in supercritical CO₂ and in bulk, and the reactivity ratios were determined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3100–3105, 2000     

The polymerization of styrene by perchloric acid at 0°

Polymerization of styrene by HClO₄ in CH₂Cl₂ at 0° at various [M]₀/[HClO₄]₀ ratios has been studied. At low values of this ratio, the reaction is second order in HClO₄ whereas it is first order at the values commonly used in kinetic studies. The rates are strongly increased by the addition of the salt benzyl trimethyl ammonium hexafluoroantimoniate, the effect being greater the lower the monomer concentration. Molecular weight distributions in the polymers formed under various conditions support the conclusion that at very low [M]₀/[HClO₄]₀ ratios the polymerization is predominantly ionic in character, and the higher order in [HClO₄]₀ is anomalous.     

(Tetracycline)europium(III) Complex as Luminescent Probe for Hydrogen Peroxide Detection

Luminescence spectra of aqueous solutions containing a fixed concentration of tetracycline (TC) and increasing concentrations of Eu³⁺ were recorded both in the absence and presence of hydrogen peroxide (H₂O₂). In H₂O₂‐free solutions in which the Eu/TC molar ratio was varied from 1 : 1 to 8 : 1, the ⁵D₀→⁷F₀ transition consisted of only one peak at 580 nm. In the presence of H₂O₂, an extra peak appeared in the spectrum at 578 nm when the Eu/TC molar ratios were above 2.5. A detailed analysis of this spectral region revealed that at lower Eu/TC molar ratios (up to 2 : 1), the ⁵D₀→⁷F₀ transition experienced a slight blue shift. This indicates that at low Eu/TC molar ratios, the presence of H₂O₂ leads to two different environments of the trivalent europium ions, which most likely form bridged peroxide complexes with hydrogen peroxide (μ‐H₂O₂ ligand). Luminescence spectra measured in the presence of molybdate ions, which catalytically decompose H₂O₂, led to the disappearance of the extra europium(III) site that was formed in the presence of H₂O₂. The intensity of the hypersensitive ⁵D₀→⁷F₂ transition did not linearly depend on the H₂O₂/TC molar ratio. For H₂O₂/TC ratios up to 10, a sharp linear increase of the peak intensity was observed, but with further increase of the H₂O₂ concentration, the intensity remained nearly constant. For H₂O₂/TC ratios above 100, the intensity of this transition even started to decrease, which limits the use of the (tetracycline)europium(III) system to quantify hydrogen peroxide in solution.     

总气压与Ar/O2流量比对直流对向靶磁控溅射TiO2薄膜光催化性能的影响

采用对向靶磁控溅射法在不同气压和Ar/O₂流量比条件下, 以氟化SnO₂ (FTO)导电玻璃为基底制备了多晶TiO₂薄膜. 台阶仪测量结果显示所制备TiO₂薄膜的平均厚度约为200 nm. 随着溅射气压的升高, TiO₂薄膜由锐钛矿与金红石混晶结构转变为纯锐钛矿结构. 分别采用场发射扫描电镜(FESEM)和原子力显微镜(AFM)分析了不同气压和Ar/O₂流量比对TiO₂薄膜表面形貌的影响, 结果显示TiO₂薄膜的表面粗糙度随溅射总气压和Ar/O₂流量比的增加而增大. 以初始浓度为100×10^-6 (体积分数)的异丙醇(IPA)气体为目标物检测所制备TiO₂薄膜的光催化性能, 并分析该气相光催化反应的机理, 在紫外照射条件下异丙醇先氧化为丙酮再被氧化为CO₂.当总溅射气压为2.0 Pa、Ar/O₂流量比为1:1时, 溅射所得TiO₂薄膜具备最优光催化活性并可在IPA降解反应中保持较高的催化活性和稳定性.     

Copolymerization of 2-Hydtoxypropyl Methacrylate with Alkyl Methacrylates

2-Hydroxypropyl methacrylate (2 HPMA) has been copolym-erized with ethyl methacrylate (EMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (EHMA) in bulk at 60°C using benzoyl peroxide as initiator. The copolymer composition has been determined from the hydroxyl content. The reactivity ratios have been calculated by the YBR method. For copolymerization of 2-HPMA (M₁) with EMA (M₂), the reactivity ratios are: r₁=1.807 ± 0.032, r₂=0.245 ± 0.021; with BMA (M₂) they are r₁=2.378 ± 0.001, r₂=0.19 ± 0.01; and with EHMA the values are r₁=4.370 ± 0.048, r₂=0.103 ± 0.006. Since the reactivity ratios are the measure of distribution of monomer units in a copolymer chain, the values obtained are compared and discussed. This enables us to choose a suitable copolymer for synthesizing thermoset acrylic polymers, which are obtained from cross-linking of hydroxy functional groups of HPMA units, for specific end uses.     

Sol–gel synthesis, characterization, and catalytic activity of Fe(III) titanates

Nanostructured iron–titanium mixed oxides with different Fe/Ti ratios were prepared by sol–gel methods under different preparative conditions. When equal molar amounts of Fe and Ti ions were employed, the product calcined at 500 °C showed an X-ray diffraction pattern that resembles Fe₂Ti₃O₉. On the other hand, lower Fe/Ti ratios favored the formation of Fe₂TiO₅ while higher ratios resulted in free α-Fe₂O₃ and TiO₂. Besides the effect of the Fe/Ti ratio, the composition of the final product was dependent on the preparative conditions and the calcination temperature. Enhancing the gelation process by heating or by employing an acid catalyst favored the formation of Fe₂TiO₅ at relatively low temperatures. Compared with the corresponding pure oxides, the prepared iron–titanium mixed oxides showed modified textural characteristics which were also dependent on the composition and the calcination temperature. The mixed oxides showed higher catalytic activity in the oxidation of methanol than their corresponding pure oxides with a noticeable enhanced oxidation potential forming methyl formate and carbon dioxide.     

Gas chromatographic analysis of aromatic carboxylic acids in the presence of C1−C22 fatty acids and C2−C16 dicarboxylic acids esterified in aqueous solutions as the n-propyl esters

Summary The direct esterification and gas chromatographic analysis of aromatic carboxylic acids as n-propyl esters is described.Derivatization is performed in aqueous solution with n-propanol in the presence of sulfuric acid. The n-propyl esters of benzoic, phthalic, trimellitic and pyromellitic acids permit their gas chromatographic separation from each other and from fatty acids and aliphatic dicarboxylic acids. At mode ratios of [H₂O]/[n-PrOH]0.03 the water present does not interfere with the esterification reaction. At mole ratios above 0.03 anhydrous sodium sulfate is used for binding the water, at mole ratios of [Na₂SO₄anh.]/[H₂O]=0.51–1.52 and of [H₂SO₄]/[Na₂SO₄anh.]=0.43–1.28, respectively.     

Etching Characteristics and Mechanisms of Mo and Al2O3 Thin Films in O2/Cl2/Ar Inductively Coupled Plasmas: Effect of Gas Mixing Ratios

An investigation of etching behaviors for Mo and Al₂O₃ thin films in O₂/Cl₂/Ar inductively coupled plasmas at constant gas pressure (6 mTorr), input power (700 W) and bias power (200 W) was carried out. It was found that an increase in Ar mixing ratio for Cl₂/Ar plasma results in non-monotonic etching rates with the maximums of 160 nm/min at 60 % Ar for Mo and 27 nm/min at 20 % Ar for Al₂O₃. The addition of O₂ in the Cl₂/Ar plasma causes the non-monotonic Mo etching rate (max. 320 nm/min at 40–45 % O₂) while the Al₂O₃ etching rate decreases monotonically. The model-based analysis of etching kinetics allows one to relate the non-monotonic etching rates in Cl₂/Ar plasma to the change in the etching regime from the ion-flux-limited mode (at low Ar mixing ratios) to the neutral-flux-limited mode (for high Ar mixing ratios). In the Cl₂/O₂/Ar plasma, the non-monotonic Mo etching rate is probably due to the change in reaction probability.