Abstract  Densities, rho, and speeds of sound, u, of binary liquid mixtures of 1-nonanol with o-xylene, m-xylene, p-xylene, ethylbenzene and mesitylene have been measured over the entire range of composition at T = (298.15 and 308.15) K and at atmospheric pressure. Using these results, the values of the excess molar volume, V-E, isentropic compressibility, kappa(S), molar isentropic compressibility, K-S,K-m, excess molar isentropic compressibility, K-S,m(E), deviations of the speed of sound, u(D), and excess partial molar volume, (V) over bar (E,0)(m,i), and excess partial molar isentropic compressibility, (K) over bar (E,0)(m,i) at infinite dilution, have been calculated. The calculated excess and deviation functions have been fitted to the Redlich-Kister polynomial equations and the results analysed in terms of molecular interactions. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract  2,3,5-Trimethylphenol (TMP) was oxidized with hydrogen peroxide employing cobalt based solid materials. K-6[CoW12O40]center dot 6H(2)O (CoW12) was probed as selective catalyst for the oxidation obtaining better results when it was supported over ZSM-5 zeolites (CoW12-ZSM-5). CoW12-ZSM-5 was found to be an efficient catalyst in the oxidation of TMP to 2,3,5-trimethylbenzoquinone (TMBQ) and 2,3,5-trimethylhydroquinone (TMHQ) under mild reaction conditions. Liquid phase reaction parameters were evaluated obtaining better results employing hydrogen peroxide as oxidant, with an oxidant/substrate molar ratio of 5, methanol as solvent and 60 degrees C as reaction temperature. An apparent activation energy of 94.19 kJ/mol was obtained. (c) 2012 Elsevier B.V. All rights reserved.

Abstract  Reaction of the doubly-bridged biscyclopentadienes (C5H4(EMe2))(C5H4(SiMe2)) (E = Si(1a), or C(1b)) with Re-2(CO)(10) in refluxing mesitylene gave the corresponding dirhenium carbonyl complexes [(eta(5)-C5H3)(2)(EMe2)(SiMe2)][Re(CO)(3)](2) (trans-2a, b and cis-2a, b), and the desilylated products [(eta(5)-C5H4)(2)(EMe2)][Re(CO)(3)](2) (3a, b). Photolysis of trans-2a, b with a series of aryl halides in benzene results in the formation of biphenyl, together with the corresponding rhenium dihalide complexes trans-[(eta(5)-C5H3)(2)(EMe2)(SiMe2)][Re(CO)(3)][Re(CO)(2)X-2] (X = Cl, Br, I) (4, 6, 8, or 10) and trans-[(eta(5)-C5H3)(2)(EMe2)(SiMe2)][Re(CO)(2)X-2](2) (5, 7, or 9). Additional experiments indicate that one phenyl ring in the resulting biphenyl comes from aryl halides and the other phenyl ring comes from the solvent benzene. However, photolysis of trans-2a with benzyl chloride and n-hexyl chloride in benzene afforded the corresponding bibenzyl and n-dodecane, as well as the rhenium dichlorides 8 and 9. In addition, complex trans-2a can also activate the C-F bond on C6F6 to form the pentafluorophenyl rhenium fluoride trans-[(eta(5)-C5H3)(2)(SiMe2)(2)][Re(CO)(3)][Re(CO)(2)(C6F5)F] (11). Molecular structures of cis-2a, cis-2b, trans-2b, 3b, 6, 7, 8, 11, and 12 determined by X-ray diffraction are also presented.

Abstract  We reported an efficient ligand-free Co(OAc)(2 center dot)4H(2)O/NaOH/O-2/ethylene glycol reaction system that enables selective aerobic oxidation of a wide range of substrates covering 2,6-di-EWG-, 2,3,6-tri-EWG-, 2-EWG-, and 2-EWG-6-EDG-substituted 4-cresols into the corresponding 4-hydroxybenzaldehydes. Based on the experimental investigations and well-defined p-benzoquinone methides, a plausible reaction mechanism was proposed. Considering the simplicity of the procedure and importance of the products, the methodology was expected to become a favorable and practical tool in related benzylic C(sp(3))-H functionalization chemistry. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract  A highly efficient and green aerobic oxidation has been developed for selectively preparing a series of valuable 2,6-dialkyl-, dialkoxyl-, and alkoxylalkyl-substituted 4-hydroxybenzaldehydes from corresponding 4-cresols in good to excellent yields, using a catalytic system of Co(OAc)(2)center dot 4H(2)O (1.0mol%)-NaOH (1.0 equiv)-O-2 (1.0atm) in aqueous ethylene glycol (EG/H2O=20/1, v/v) at 50 degrees C. Furthermore, a plausible mechanism was proposed for the direct oxyfunctionalization of the aromatic methyl group into the aldehyde group.

Abstract  Bis(pyridinium salt)s containing different alkyl chain lengths and various organic counterions were prepared by the ring-transmutation reaction of bis(pyrylium tosylate) with aliphatic amines in dimethyl sulfoxide at 130-135 degrees C for 18 h and their tosylate counterions were exchanged to other anions such as triflimide, methyl orange, and dioctyl sulfosuccinate by the metathesis reaction in a common organic solvent. Their chemical structures were established by using H-1, F-19, and C-13 NMR spectra. The thermal properties of bis(pyridinium salt)s were studied by DSC and TGA measurements. Some of the dicationic salts provided low melting points below 100 degrees C and some of them displayed amorphous properties. Polarized optical microscopy studies revealed the crystal structures prior to melting temperatures in some cases. Their optical properties were examined by using UV-Vis and photoluminescent spectrometers; and they emitted blue light both in the solution and solid states regardless of their microstructures, counterions, and the polarity of organic solvents. However, most of these salts exhibited hypsochromic shifts in their emission peaks in the solid state when compared with those of their solution spectra. Due to unique properties of methyl orange anion as a pH indicator, two of the salts showed different color change in varying concentrations of triflic acid in common organic solvents, demonstrating their potential use as an acid sensor in methanol, acetonitrile and acetone. (C) 2013 Elsevier B.V. All rights reserved.

Abstract  The AuCl3-catalyzed nitrene insertion into an aromatic C-H bond of mesitylene demonstrates a unique activity and chemoselectivity in direct C-H aminations. Mechanisms for catalytic nitrene insertion are examined here using theory. The AuCl3 catalyst favors formation of a complex with the PhI═NNs (Ns = p-nitrobenzenesulfonyl) substrate, followed by the appearance of the key (N-chloro-4-nitrophenylsulfonamido)gold(III) chloride intermediate (INT5). However, the putative gold(III)-nitrene analogue (AuCl3-NNs complex) is thermodynamically unfavorable compared with INT5. Therefore, INT5 is suggested to play a critical role in the AuCl3-promoted aromatic C-H bond amination, a prediction in contrast to the previously reported crucial metal-nitrene intermediates. The activation of a C(sp(2))-H bond of mesitylene via σ-bond metathesis is proposed based on INT5, and the subsequent detailed pathways for the aromatic C-H bond amination are computationally explored. A chemoselective nitrene insertion into a mesitylene aromatic C-H bond, instead of a benzylic C-H bond, is rationalized for the AuCl3-catalyzed amination.

Abstract  The combustion of fossil fuels forms polycyclic aromatic hydrocarbons (PAHs) composed of five- and six- membered aromatic rings, such as indene (C9 H8 ), which are carcinogenic, mutagenic, and deleterious to the environment. Indene, the simplest PAH with single five- and six-membered rings, has been predicted theoretically to be formed through the reaction of benzyl radicals with acetylene. Benzyl radicals are found in significant concentrations in combustion flames, owing to their highly stable aromatic and resonantly stabilized free-radical character. We provide compelling experimental evidence that indene is synthesized through the reaction of the benzyl radical (C7 H7 ) with acetylene (C2 H2 ) under combustion-like conditions at 600 K. The mechanism involves an initial addition step followed by cyclization and aromatization through atomic hydrogen loss. This reaction was found to form the indene isomer exclusively, which, in conjunction with the high concentrations of benzyl and acetylene in combustion environments, indicates that this pathway is the predominant route to synthesize the prototypical five- and six-membered PAH.

Abstract  In this contribution, we report on novel functionalized triazines, which represent new precursors for C/N/(H) compounds or suitable building blocks for carbon-based functional networks. Our results provide insights into the structural properties of molecular carbon nitride materials and their design principles. Tris(1-propynyl)-1,3,5-triazine (C3 N3 (C3 H3 )3 ) and tris(1-butynyl)-1,3,5-triazine (C3 N3 (C4 H5 )3 ) were prepared by substitution reactions of cyanuric chloride (C3 N3 Cl3 ) with prop-1-yne and but-1-yne. The crystal structure of tris(1-propynyl)-1,3,5-triazine was solved in the orthorhombic space group Pbcn (Z=4, a=1500.06 (14), b=991.48(10), c=754.42(6) pm, V=1122.03(18)×10(6)  pm(3) ), whereas tris(1-butynyl)-1,3,5-triazine crystallized in the triclinic space group P-1 (Z=6, a=1068.36(12), b=1208.68(12), c=1599.38(16) pm, α=86.67(3), β=86.890(4), γ=86.890(4)°, V=1997.7(4)×10(6)  pm(3) ). For both structures, planar triazine units and layerlike packing of the molecules were observed. Tris(1-propynyl)-1,3,5-triazine is built up from hydrogen-bonded zig-zag strands, whereas tris(1-butynyl)-1,3,5-triazine shows parallel layered arrangements. Both compounds were investigated by NMR spectroscopy, IR spectroscopy, and differential thermal analysis/thermogravimetric analysis, which provided insights into their structural, chemical, and thermal properties. In addition, tris(1-propynyl)-1,3,5-triazine was pyrolyzed and a new polymeric triazine-based compound containing mesitylene units was obtained. Its structural features and properties are discussed in detail.

Abstract  The effect of silicon nanowire (Si NW) diameter on the functionalization efficiency as given by covalent Si-C bond formation is studied for two distinct examples of 25 ± 5 and 50 ± 5 nm diameters (Si NW25 and Si NW50, respectively). A two-step chlorination/alkylation process is used to connect alkyl chains of various lengths (C1-C18) to thinner and thicker Si NWs. The shorter the alkyl chain lengths, the larger the surface coverage of the two studied Si NWs. Increasing the alkyl chain length (C2-C9) changes the coverage on the NWs: while for Si NW25 90 ± 10% of all surface sites are covered with Si-C bonds, only 50 ± 10% of all surface sites are covered with Si-C bonds for the Si NW50 wires. Increasing the chain length further to C14-C18 decreases the alkyl coverage to 36 ± 6% in thin Si NW25 and to 20 ± 5% in thick Si NW50. These findings can be interpreted as being a result of increased steric hindrance of Si-C bond formation for longer chain lengths and higher surface energy for the thinner Si NWs. As a direct consequence of these findings, Si NW surfaces have different stabilities against oxidation: they are more stable at higher Si-C bond coverage, and the surface stability was found to be dependent on the Si-C binding energy itself. The Si-C binding energy differs according to (C1-9)-Si NW > (C14-18)-Si NW, i.e., the shorter the alkyl chain, the greater the Si-C binding energy. However, the oxidation resistance of the (C2-18)-Si NW25 is lower than for equivalent Si NW50 surfaces as explained and experimentally substantiated based on electronic (XPS and KP) and structure (TEM and HAADF) measurements.

Abstract  An untargeted metabolomics workflow for the detection of metabolites derived from endogenous or exogenous tracer substances is presented. To this end, a recently developed stable isotope-assisted LC-HRMS-based metabolomics workflow for the global annotation of biological samples has been further developed and extended. For untargeted detection of metabolites arising from labeled tracer substances, isotope pattern recognition has been adjusted to account for nonlabeled moieties conjugated to the native and labeled tracer molecules. Furthermore, the workflow has been extended by (i) an optional ion intensity ratio check, (ii) the automated combination of positive and negative ionization mode mass spectra derived from fast polarity switching, and (iii) metabolic feature annotation. These extensions enable the automated, unbiased, and global detection of tracer-derived metabolites in complex biological samples. The workflow is demonstrated with the metabolism of (13)C9-phenylalanine in wheat cell suspension cultures in the presence of the mycotoxin deoxynivalenol (DON). In total, 341 metabolic features (150 in positive and 191 in negative ionization mode) corresponding to 139 metabolites were detected. The benefit of fast polarity switching was evident, with 32 and 58 of these metabolites having exclusively been detected in the positive and negative modes, respectively. Moreover, for 19 of the remaining 49 phenylalanine-derived metabolites, the assignment of ion species and, thus, molecular weight was possible only by the use of complementary features of the two ion polarity modes. Statistical evaluation showed that treatment with DON increased or decreased the abundances of many detected metabolites.

Abstract  The results of density matrix renormalization group complete active space self-consistent field (DMRG-CASSCF) and second-order perturbation theory (DMRG-CASPT2) calculations are presented on various structural alternatives for the O-O and first C-H activating step of the catalytic cycle of the binuclear nonheme iron enzyme Δ(9) desaturase. This enzyme is capable of inserting a double bond into an alkyl chain by double hydrogen (H) atom abstraction using molecular O2. The reaction step studied here is presumably associated with the highest activation barrier along the full pathway; therefore, its quantitative assessment is of key importance to the understanding of the catalysis. The DMRG approach allows unprecedentedly large active spaces for the explicit correlation of electrons in the large part of the chemically important valence space, which is apparently conditio sine qua non for obtaining well-converged reaction energetics. The derived reaction mechanism involves protonation of the previously characterized 1,2-μ peroxy Fe(III)Fe(III) (P) intermediate to a 1,1-μ hydroperoxy species, which abstracts an H atom from the C10 site of the substrate. An Fe(IV)-oxo unit is generated concomitantly, supposedly capable of the second H atom abstraction from C9. In addition, several popular DFT functionals were compared to the computed DMRG-CASPT2 data. Notably, many of these show a preference for heterolytic C-H cleavage, erroneously predicting substrate hydroxylation. This study shows that, despite its limitations, DMRG-CASPT2 is a significant methodological advancement toward the accurate computational treatment of complex bioinorganic systems, such as those with the highly open-shell diiron active sites.

Abstract  In the title mol-ecular salt, C22H21FI(+)·CF3SO3 (-), the dihedral angle between the rings of the biphenyl group is 65.6 (1)°. The ring of the mesitylene group is inclined to the fluoro-benzene ring at an angle of 86.1 (3)° and the C-I-C bond angle is 97.0 (2)°. In the crystal, extremely short I⋯O contacts of 2.862 (5) and 2.932 (5) Å occur, due to the strong electrostatic inter-actions between the I atom and two adjacent tri-fluoro-methane-sulfonate counter-ions. There are also C-H⋯F and C-H⋯π inter-actions present: together with the I⋯O bonds, these result in a three-dimensional network.

Abstract  A rigid 3-connecting triacid MeBTB was designed and synthesized in the quest of guest inclusion in the pores of honeycomb network structures generated based on the acid dimer-mediated self-assembly. Crystallization of MeBTB is indeed found to lead to a (6,3) net that is 3-fold interpenetrated. Charge-assisted hydrogen bond-mediated self-assembly in the presence of KX/dibenzo-18-crown-6 is likewise found to lead to a (3,3) honeycomb net, which is also 3-fold interpenetrated. When contrasted with the results of self-assembly of sterically-unhindered 1,3,5-benzenetribenzoic acid 2 and those of analogous tribenzoic acid based on mesitylene, that is MTB, the sterics built into the structure of MeBTB allow engineering of ordered assemblies with reduced interpenetration and higher solvent-accessible volumes. A limited, yet meaningful number of structures demonstrates the fact that the rigid building blocks, while responding to the expectations based on aggregation via acid dimer synthon, are most likely to present rich diversity in terms of synthon adoptions and bring up surprises in the self-assembly through inclusion of adventitious water. Crystallization of MeBTB in MeOH-DME led to a disappearing solvate form in which the helically organized acids are found to sustain a water channel.

Abstract  The origins of the absorption spectroscopy of pterin and Re(CO)3(pterin)(H2O) complex as a function of pH is studied using the hybrid functional B3LYP and PBE0 in combination with 6-311++G(d,p) and LanL2TZ(f) basis sets. A natural bond analysis was performed to the principal molecular orbitals involved in the electronic transitions of the studied compounds. The low energy band of pterin, which is described as a H→L electronic transition, can be interpreted as an admixture of π→π(*), n→π(*) and n→n electronic transitions involving π(C2-N1, C6-N5, C9-C10) and n(C2) orbitals of the HOMO and π(*)(C6-N5, C7-N8) and n(C4) orbitals of the LUMO. The low energy band of Re(CO)3(pterin)(H2O) can be described as a combination of different MLLCT transitions where electron density residing on different π orbitals of carbonyl-Re bonds and lone pairs of Re is transferred to pterin moiety. Besides MLLCT transitions, IL, LLCT and LLMCT transitions contribute the absorptions of the Re(I) complex in the wavelength region corresponding to the high energy bands. The calculated electronic spectra of the acid and base forms of pterin and Re(CO)3(pterin)(H2O) were simulated from the theoretical results and compared to the experimental absorption spectra with great accuracy both in position and relative intensities of the absorption bands.

Abstract  The folding preferences of two capped, constrained β/γ-dipeptide isomers, Ac-βACPC-γACHC-NHBn and Ac-γACHC-βACPC-NHBn, (designated βγ and γβ, respectively), have been investigated using single- and double-resonance ultraviolet and infrared spectroscopy in the gas phase. These capped β/γ-dipeptides have the same number of backbone atoms between their N- and C-termini as a capped α-tripeptide and thus serve as a minimal structural unit on which to test their ability to mimic the formation of the first turn of an α-helix. Resonant two-photon ionization and UV-UV hole-burning spectroscopy were performed in the S0-S1 region, revealing the presence of three unique conformations of βγ and a single conformation of γβ. Resonant ion-dip infrared spectra were obtained in the NH stretch region from 3300 to 3500 cm(-1) and in both the amide I and amide II regions from 1400 to 1800 cm(-1). These infrared spectra were compared to computational predictions from density functional theory calculations at the M05-2X/6-31+G(d) level, leading to assignments for the observed conformations. Two unique bifurcated C8/C13 H-bonded ring structures for βγ and a single bifurcated C9/C13 H-bonded ring structure for γβ were observed. In all cases, the H-bonding patterns faithfully mimic the first full turn of an α-helix, most notably by containing a 13-membered H-bonded cycle but also by orienting the interior amide group so that it is poised to engage in a second C13 H-bond as the β/γ-peptide lengthens in size. The structural characteristics of the β/γ-peptide version of the 13-helix turn are compared with the α-helix counterpart and with a reported crystal structure for a longer β/γ-peptide oligomer.

Abstract  In contrast to common ferroelectric smectic C* liquid crystals, the siloxane-terminated smectic mesogen E6 is characterized by an unusual temperature variation of the spontaneous polarization. The polarization starts to grow from nearly zero despite the first-order SmA*-SmC* transition, and increases faster than linearly over a large temperature interval while the tilt angle rapidly saturates. To study this behavior in more detail, binary mixtures of different concentrations of E6 in the achiral SmC material C8Cl, which has a similar chemical structure, were investigated. Surprisingly, all mixtures show a temperature dependent polarization sign inversion, which shifts towards the SmC*-SmA* transition with increasing E6 concentration. For the pure E6 the inversion temperature meets the SmA*-SmC* phase transition temperature. In a second binary mixture with E6 and a conventional material C9-2PhP we found out, that the dependence of the inversion temperature on the concentration of E6 changes qualitatively when the nanosegregation is partially destroyed. A molecular theory of the polarization sign inversion in smectics C* with strong polar intermolecular interactions is developed which enables one to explain the concentration dependence of the inversion temperature in both mixtures.

Abstract  This paper describes the ability of a new class of heterocyclic γ-amino acids named ATCs (4-amino(methyl)-1,3-thiazole-5-carboxylic acids) to induce turns when included in a tetrapeptide template. Both hybrid Ac-Val-(R or S)-ATC-Ile-Ala-NH2 sequences were synthesized and their conformations were studied by circular dichroism, NMR spectroscopy, MD simulations, and DFT calculations. It was demonstrated that the ATCs induced highly stable C9 pseudocycles in both compounds promoting a twist turn and a reverse turn conformation depending on their absolute configurations. As a proof of concept, a bioactive analogue of gramicidin S was successfully designed using an ATC building block as a turn inducer. The NMR solution structure of the analogue adopted an antiparallel β-pleated sheet conformation similar to that of the natural compound. The hybrid α,γ-cyclopeptide exhibited significant reduced haemotoxicity compared to gramicidin S, while maintaining strong antibacterial activity.

Abstract  Study on use of aviation fuels in the internal combustion engines in road vehicles has been conducted for a long time. After the JP-8 is accepted as a single fuel on land and in the air (single fuel concept) by the North Atlantic Treaty Organization (NATO), the majority of these studies have focused on JP-8. For this reason, there is hardly any study on using the Jet A1, which is structurally very similar to the JP-8, in the internal combustion engine. However, in obligatory cases such as in periods of war, using the Jet A1 in the same way as the JP-8 in internal combustion engines may be required. In cold climates especially, the Jet A1 may gain strategic importance due to its very low freezing point. In this study, both the effects of the diesel and Jet A1 blends on engine performance and exhaust emissions in both the single cylinder, and the direct injection diesel engine have been examined. As a result, it has been determined that use of Jet A1 reduces engine torque to 5.85% and increases the specific fuel consumption to 8.77%. In addition, while there is an increase in smoke and carbon monoxide (CO) emissions 82% and 71.9%, respectively, there is a decrease in nitrogen oxide (NOx) emissions by 29%. In conclusion, there is no positive effect in using the Jet A1 in the diesel engine except for the reduction of NOx emission and the decrease of the freezing point.

Abstract  Particulate emissions were collected from an Auxiliary power unit (APU) directly upon TEM grids for particle characterization by HRTEM. Carbonaceous emissions from two fuels, a coal-based Fischer-Tropsch and standard JP-8 were compared, each at three power levels. Differences in soot nanostructure, specifically fullerenic content reveal changes in the combustion chemistry with engine power level, as do differences in aggregate size between the two fuels. As inferred from the soot nanostructure, comparison between fuels demonstrates the impact of fuel structure upon soot formation chemistry. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract  The study of the energetics of phenolic compounds has a considerable practical interest since this family of compounds includes numerous synthetic and naturally occurring antioxidants. In this work, density functional theory (DFT) has been used to investigate gas-phase thermochemical properties of the following tri-substituted phenols: 2,4,6-trimethylphenol, 2,6-dimethyl-4-tert-butylphenol, 2, 6-dimethyl-4-methoxyphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tertbutyl-4-methoxyphenol, 2,4,6-trimethoxyphenol, 2,6-dimethoxy-4-methylphenol and 2,6-dimethoxy-4-tert-butylphenol. Molecular structures were computed with the B3LYP and the omega B97X-D functionals and the 6-31G(d) basis set. More accurate energies were obtained from single-point energy calculations with both functionals and the 6-311++G(2df,2pd) basis set. Standard enthalpies of formation of the phenolic molecules and phenoxyl radicals were derived using an appropriate homodesmotic reaction. The O-H homolytic bond dissociation enthalpies, gas-phase acidities and adiabatic ionization enthalpies were also calculated. The general good agreement found between the calculated and the few existent experimental gas-phase thermochemical parameters gives confidence to the estimates concerning the phenolic compounds which were not yet experimentally studied. (C) 2014 Elsevier Ltd. All rights reserved.

Abstract  We resolved the controversial assignments of the visible vibronic bands observed from corona discharge of 1,2,3-trimethylbenzene. The vibronic bands belonging to the jet-cooled 2,6-dimethylbenzyl radical were clearly identified from the spectrum observed from corona discharge of 2,6-dimethylbenzyl chloride. After subtracting the bands of the 2,6-isomer from the spectrum observed from corona discharge of 1,2,3-trimethylbenzene, the vibronic bands of the 2,3-isomer were also identified. By comparing data with the known vibrational data of 1,2,3-trimethylbenzene and the results of ab initio calculations, we determined the electronic energies of the D-1 -> D-0 transitions and vibrational mode frequencies in the ground electronic states of the 2,3-and 2,6-dimethylbenzyl radicals.

Abstract  Secondary organic aerosol (SOA) from the photooxidation of aromatic compounds is a very complex mixture containing products with a different chemical nature that are dependent on aging processes. Aging of SOA particles formed from OH-initiated oxidation of benzene was investigated in a home-made smog chamber in this study. The chemical composition of aged benzene SOA particles were measured using aerosol laser time-of-flight mass spectrometer (ALTOFMS) coupled with Fuzzy C-Means (FCM) clustering algorithm. Experimental results showed that nitrophenol, dinitrophenol, nitrocatechol, dinitrocatechol, 6-oxo-2,4-hexadienoic acid, 2,4-hexadiendioic acid, 2,3-dihydroxy-6-oxo-4-hexenoic acid, 2,3-epoxy-4-hexendioic acid, 2,3-epoxy-4,5-dihydroxy-hexanedioic acid and high-molecular-weight (HMW) components were the predominant products in the aged particles. Compared to offline method such as liquid chromatography mass spectrometry (LC-MS) measurement, the real-time ALTOFMS detection approach coupled with the FCM data processing algorithm can make cluster analysis of SOA successfully and provide more information of products. The present results also indicate that benzene SOA aging proceeds through the oxidation of the internal double bond of ring-opened products, phenolic compounds, and acid-catalyzed heterogeneous reactions of carbonyl products. The possible reaction mechanisms leading to these aged products were also discussed and proposed.

Abstract  A series of mesoporous sieves with different pore diameters and structures have been controllably synthesized by adding variable amounts of swelling agent 1,3,5-trimethylbenzene in the preparation process for SBA-15. NiMo catalysts supported by mesoporous sieves are prepared by using the newly proposed Mo-based organic-inorganic hybrid nanocrystals as precursors to load Mo and subsequently using wetness impregnation to load Ni. The hydrodesulfurization (HDS) activity of these obtained catalysts is evaluated in a continuously flowing tubular fixed-bed microreactor using 1 wt% dibenzothiophene (DM.) in heptane as a model compound. The results show that HDS ratio has gradually increased as the pore diameter of supports is enlarged from 7 to 11 nm with the mesostructure keeping an ordered two-dimensional hexagonal symmetcy. When the structure is in the intermediate stage of structural transition from ordered hexagonal mesostructure to mesocecullar structure, HDS ratio is decreased dramatically due to the disordered and collapsed structure to block the pore channels. After the mesocecullar structure with three-dimensional open pore channels is formed which is more convenient for the molecular diffusion, HDS ratio has increased again as a result It is concluded that both the pore size and window size connecting the adjacent pores play an important role in the HDS activity but the window size is of more significant importance, which is the key point for the enhanced catalytic performance. (c) 2014 Elsevier Ltd. All rights reserved,