乙醛二聚体的从头计算

用ab initio分子轨道法在STO-3G和6-31G水平上, 全构型优化, 对二聚乙醛的各种稳定构型进行了研究。结果表明, 在STO/6-31G水平上, 最稳定的乙醛二聚体为具有对称中心的环状结构, 包含由醛基氢和醛基氧组成的二个C—H…O氢键。结合能为-20.17 kJ·mol~(-1), 与实验估计的结合能-22.39±0.15 kJ·mol~(-1)比较接近。STO-3G过低估计了乙醛二聚体的结合能, 在不同构型的相对稳定性方面也与6-31G不一致。     

DEMS study on the nature of acetaldehyde adsorbates at Pt and Pd by isotopic labelling

The formation of acetaldehyde adsorbates on Pt and Pd has been studied applying cyclic voltammetry and differential electrochemical mass spectrometry (DEMS). The adspecies were isolated on the metal surface at selected adsorption potentials (E _ad) applying a flow cell procedure under potential control, and the anodic stripping were performed for each E _ad. For Pt, two different contributions were established during oxidation: one at E < 0.80 V and the second in the range 0.80–1.50 V in the Pt oxide region. For Pd, the voltammetric profile resembles that for the oxidation of adsorbed CO. DEMS experiments have shown that CO₂ was the sole electro-oxidation product in both cases. The oxidation of each C atom in acetaldehyde adsorbates has been distinguished using the isotopic-labelled aldehyde in DEMS experiments at selected E _ad. It was observed that, on Pt, acetaldehyde molecules loose part of the CH₃ groups during adsorption at E _ad < 0.40 V, whereas the CHO groups are easily oxidized at E _ad > 0.40 V. Therefore, both C₁ and C₂ species are present on the surface, and their yields depend on E _ad. On the contrary, on Pd, most of the CH₃ groups are lost during adsorption at all E _ad, and the main adsorbed species seems to be CO_ad. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

Effect of electrolysis conditions on photocatalytic activities of the anodized TiO2 films

Photocatalytic activities of anodized TiO₂ films for decomposition of gaseous acetaldehyde were investigated. The anodized TiO₂ films were fabricated by galvanostatic anodization in a mixed electrolyte composed of H₂SO₄, H₃PO₄, and H₂O₂. Pre-nitridation treatment effectively enhanced the photocatalytic activity of the anodized TiO₂ films. The electrolysis parameters such as anodization time, current density, electrolyte temperature, and electrolyte composition significantly affected the photocatalytic activity of the anodized TiO₂ films. The improvement of photocatalytic activity of the anodized films is attributed to increase in surface areas of the anodized specimens.     

On the origin of the barriers and the structures of acetaldehyde in its ground and first singlet excited state

Summary Anab initio study of the ground and the first singlet excited states of acetaldehyde has been performed to analyze the molecular properties as a function of the methyl torsion and the aldehydic hydrogen wagging angles. The structural characteristics and the conformational behaviour in both electronic states have been determined. The important structural changes between the two states have been analyzed by a decomposition of the total energy into its components. It was found that the methyl torsion barriers arise mainly from attractive interactions. Evidence is presented which shows that these barriers arise from in-plane and out-of-plane hyperconjugative effects involving the oxygen atom. It is also shown that the pyramidalization experienced by the carbonyl carbon in the first singlet excited state has two sources, namely, a decrease in the electronic repulsion and an increase in the electron-nucleus attraction.     

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV–Vis detection

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 L phosphoric acid 1 mol L^–1 at a controlled room temperature of 15°C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C₁₈ column, using methanol/LiCl_(aq) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV–Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3–300 mg L^–1 per injection (20 L) and the limit of detection (LOD) for acetaldehyde was 2.03 g L^–1, with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n=5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7–102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.     

Electrocatalytic Activity of Pt/C Electrodes for Ethanol Oxidation in Vapor Phase

Introduction The selective oxidation of ethanol to acetaldehydeis of special interest in the areas where biomass-basedeconomics are under development since acetaldehydecan be used for the syntheses of other basic chemicalssuch as acetic acid, acetic anhydride,n-butanol,etc.[1—6]. With the advancement of fuel cell technologyand electrocatalysis stimulated by the world energy andraw material situation, some special opportunities havebeen provided for investigating electrosynthesis of or-ganic c…     

Electrospinning fabrication of rime-like NiO nanowires/nanofibers hierarchical architectures and their photocatalytic properties

Rime-like NiO Nanowires/nanofibers hierarchical architectures have been fabricated employing a co-precipitation reaction and electrospinning method. The synthesized hierarchical structure was characterized using SEM, XRD and BET analysis methods. The effects of growth temperature and reaction time on the morphologies of the as-prepared structures were investigated by SEM characterization and a possible mechanism for the formation of NiO hierarchical structures is proposed. Based on the nitrogen adsorption and desorption measurements, the BET surface area of the as-obtained sample is 61.0 m²/g and the pore sizes of ca. 5.0 nm. The catalytic efficiency of the NiO nanomaterials developed was evaluated by the photocatalytic degradation of acetaldehyde. In comparison with sphere-like and fiber-like structures, the NiO hierarchical structures show an excellent ability to rapidly acetaldehyde pollutant, which may be attributed to its unique hierarchical and porous surface structures.     

A theoretical study for one-dimensional modeling for VOC in a catalytic converter

Modeling for catalytic oxidation of a volatile organic compound, acetaldehyde for the purpose of controlling tail-pipe emissions from vehicular exhaust was carried out. The model developed was one-dimensional unsteady state model, using mass and energy balance equations to predict results for acetaldehyde conversion in an adiabatic monolith operating under warm-up conditions. The equations consisted of a set of partial differential equations that are coupled and solved using Backward Implicit Scheme. Analysis of the behavior of the converter during warm up period was carried out and it was observed that the warm up was faster for a fresh catalyst and this warm up period could be reduced by introducing hot incoming exhaust gas at higher temperature.     

Novel applications for headspace gas chromatography

Summary New application areas for headspace gas chromatography in agricultural and polymer degradation research are described. Specific examples are drawn from the various forms of headspace analysis with emphasis on the automated static equilibrium method.Presented at the 32nd Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 9–13, 1981, Atlantic City, NJ (Paper No. 598).     

An application of transparent mesoporous bulk silica to a titanium dioxide photocatalyst with adsorption and decomposition functions

Mesoporous bulk silica with optical transparency and high porosity can be prepared using a gel-templating method. This unique material has potentially wide-ranging applications as containers of specific molecules, smart deliverers of target molecules, and photonic devices. Among the potential applications, the use of silica as a photocatalyst is explored in this paper; the photocatalyst was prepared by loading titanium dioxide (titania) from the titania precursor solution into the mesoporous structure of silica with a controlled pore size. Even after crystallization, the titania-loaded silica remained highly mesoporous with uniform pore size and optical transparency. The ability of the adsorption and decomposition of acetaldehyde gas was evaluated by measuring the concentration change of the gas with and without the irradiation of ultraviolet rays. As a result, the specific surface area, the amount of titania and the calcination temperature were essential in determining the adsorption ability as well as the decomposition ability.