Determination of oxygenated compounds in secondary organic aerosol from isoprene and toluene smog chamber experiments

The determination of multifunctional oxygenated compounds in secondary organic aerosols (SOA) usually requires a derivatisation protocol prior to gas chromatography-mass spectrometry analysis (GC-MS). Our proposed protocol, a combination of O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) plus diluted N-methyl-N-trimethyl-silyltrifluoroacetamide (MSTFA) without catalyst, has improved the determination of carbonyls, polyhydroxyl-compounds, hydroxyl-carbonyls, hydroxyl-carboxylic acids and di-carboxylic acids. The optimised derivatisation protocol has been successfully used for blanks, standard mixtures and photo-oxidation products from isoprene and toluene generated in a high-volume simulation chamber (European Photoreactor, EUPHORE).

Some previously identified degradation products for isoprene including tetrols such as threitol, erythritol; 2-methyltetrols and 2-methylglyceric acid; and for toluene including nitrophenols, methyl-nitrophenols, benzaldehyde, p-cresol, benzoic acid, glyoxylic acid and methyl-glyoxylic acid, have been identified in our aerosol samples, thus confirming the successful applicability of the proposed derivatisation protocol. Moreover, the reduction of artefacts and enhanced signal-to-noise ratio, have allowed us to extend the number of multifunctional compounds determined. These findings have demonstrated the validity of this analytical strategy, which will contribute to a better understanding of the atmospheric degradation chemistry of biogenic and anthropogenic pollutants.     

焙烧温度对Ni/γ-Al_2O_3还原条件及催化甲苯水蒸气重整反应的影响

研究了焙烧温度对Ni/γ-Al2O3还原条件及催化甲苯水蒸气重整反应的影响。结果表明,焙烧温度对催化剂的还原条件及性能具有重要影响。700℃焙烧的催化剂在680℃的反应温度下表现出良好的反应性能,在不进行预还原的情况下仍保持了很高的催化活性及稳定性,其中,甲苯转化率达99%。并使用BET、XRD、TG-DTG等表征方法对反应前后的催化剂进行表征,随着焙烧温度的升高,催化剂比表面积降低、总孔容减小、平均孔径增大、镍与载体的结合程度逐渐增强、NiAl2O4含量逐渐增多,这是焙烧温度影响催化剂还原条件的主要原因。最后通过TEM、XPS对700℃焙烧的催化剂的结构进行了进一步的分析。     

超强碱K2O对甲苯甲醇侧链烷基化反应的影响

采用离子交换法、浸渍法和焙烧分解法制备了x%K2O/KLSX(x = 0, 1, 2, 3, 4)催化剂,KLSX上的超强碱性位K2O通过KNO3分解制得。考察了x%K2O/KLSX的甲苯甲醇侧链烷基化反应催化性能及超强碱性位K2O对反应的影响。超强碱性位K2O可以更好的极化甲苯甲基,以及催化甲醇转化为烷基化中间体,甚至完全分解为CO和H2。KLSX 和 1%K2O/KLSX因碱性较弱所以活性较低,3%K2O/KLSX和4%K2O/KLSX因含超强碱性位太多和可利用L酸性位太少,其活性也很低。相比之下,2%K2O/KLSX具有足够量的弱L酸位来吸附甲苯,以及适当强度的碱性位来转化甲醇和活化甲苯甲基,因此具有较高的催化甲苯甲醇侧链烷基化反应活性。     

钴/碳纤维电化学催化氧化甲苯性能研究

以纤维状活性碳吸附Co2+作为电极,在水溶液体系中,高效吸附-电化学催化氧化两步联动法矿化处理气态甲苯。实验结果显示,甲苯通过电化学反应器后能够被有效的降解。在电流密度为0.05 A·cm-2,电解电压为12 V,鼓气速率为80 L·h-1的条件下,甲苯的去除率达90%以上。甲苯降解后的主要产物为苯甲酸。     

Effect of ZSM-5 zeolite morphology on the catalytic performance of the alkylation of toluene with methanol

A series of ZSM-5 zeolites, with the morphologies of sphere, sphere with cubic particles on the surface, and cubic particles, were synthesized by hydrothermal method using n-butylamine as the template, assisted by the addition of NaCl and crystal seed. X-ray diffraction(XRD),scanning electron microscope(SEM), X-ray fluorescence(XRF) and temperature-programmed desorption of ammonia(NH3-TPD) were used to characterize these samples. The samples were tested with toluene methylation reaction. The modified sample composed of spherical particles with 3 μm crystal particles on the surface had a para-xylene selectivity of 95% and maintained 79% of the initial conversion after running the reaction for 50 h. This modified sample showed the best stability among the tested three modified samples.     

Titanium dioxide nanotube fiber using in headspace solid-phase microextraction with GC–MS for BTEX detection

Anodized TiO₂ nanotube fibers using in-headspace solid-phase microextraction (SPME) with gas chromatography–mass spectrometry (GC–MS) have been exploited as an analytical method for volatile organic compounds such as benzene, toluene, ethylbenzene, and xylenes (BTEX) detection. The factors of anodizing time and annealing temperature for TiO₂ nanotube production are studied and the adsorption factors (time, ionic strength, and temperature) and desorption factors (time and temperature) for BTEX analysis are optimized. The limit of detections (LODs) for benzene, toluene, ethylbenzene o-xylene, and m, p-xylene are 0.5, 0.1, 1.0, 1.0, and 2.0 μg L⁻¹, respectively. The linear ranges for BTEX (0.5–15,000 μg L⁻¹) and satisfactory linearity (R² ≥ 0.9954) are obtained. This method is successfully applied in real samples with the recoveries ranging from 92% to 97%. TiO₂ nanotube fiber is a promising technique for BTEX analysis.     

Analysis of preparation of TiO<Subscript>2</Subscript> particles by diffusion flame reactor for photodegradation of phenol and toluene

TiO₂ nanoparticles were produced in the diffusion flame reactor, and the size and anatase/rutile content of TiO₂ were examined by a Particle Size Analyzer and X-ray diffraction, respectively. Increase in fuel/O₂ ratio, initial concentration of TiCl₄ or total gas flow rate causes the larger particle size and the higher rutile composition. The photocatalytic activities of TiO₂ powders were tested on the decompositions of phenol and toluene in the aqueous solution under UV irradiation. The degradation rate increases as the TiO₂ particle size decreases and as the initial concentration of phenol or toluene increases. The photodegradation rate of phenol by TiO₂ particles is higher than that of toluene at the same process conditions. The computational method was used to simulate the gas temperature, velocity and species mass fractions inside the diffusion flame reactor during synthesis of TiO₂ nanoparticles. The measured and simulated temperature results were compared on several positions above the burner and both of them show good agreements. The typical contours of TiCl₄, TiO₂ mass fractions and gas velocities in flame reactor were presented.     

用于甲苯催化燃烧的Pd/Ce0.8Zr0.2O2/基底整体催化剂

采用浸渍法制备了Pd/Ce0.8Zr0.2O2/基底整体催化剂,应用热重-差示扫描量热、扫描电镜、X射线衍射、氮吸附、拉曼光谱和程序升温还原等技术手段对催化剂进行了表征,考察了不同温度焙烧的整体催化剂的甲苯催化燃烧性能.结果表明,一层均匀紧密的Ce0.8Zr0.2O2涂层很好地分散在基底表面上,该涂层具有良好的抗振荡性和较高的粘结强度.400℃焙烧的Pd/Ce0.8Zr0.2O2/基底整体催化剂的催化活性最高,甲苯转化率达97%以上的最低反应温度为210℃.此外,Pd/Ce0.8Zr0.2O2/基底整体催化剂具有良好的热稳定性,这可能是因为CeO2-ZrO2固溶体的形成和高温下PdO的稳定存在.     

Intramolecular reorganization 1. Deprotonation of toluene with the CH<Subscript>2</Subscript>CN<Superscript>−</Superscript> anion: an analysis in the framework of a gas-phase model

A mechanism is proposed of intramolecular reorganization leading to equalization of the energies of reactants and products in a nonequilibrium proton transfer reaction. The model proposed allows one to extend a conventional quantum chemical treatment to gas-phase proton transfer. Taking the reaction of toluene deprotonation with the CH₂CN⁻ anion (a conjugate base of acetonitrile) as an example, it was shown that the activation energy and its components can be determined from direct ab initio calculations. The effect of disbalance of structural changes relative to the “equilibrium” proton transfer is considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1808–1815, September, 2008.