Effect of temperature on the diffusion mechanism of xylene isomers in a FAU zeolite: a molecular dynamics study

The diffusion of o-, m-, and p-xylene in a FAU zeolite at 300-900 K was investigated using molecular dynamics simulations. Calculated self-diffusion coefficients of xylene isomers showed that the mobility of p-xylene was the fastest, m-xylene the second fastest, and o-xylene the slowest in the FAU zeolite at the same temperature. The diffusion activation energy of o-xylene, m-xylene and p-xylene was, respectively, determined to be 9.04, 7.45 and 6.44 kJ mol(-1) within the temperature range of 400 to 900 K, while to be 14.12, 13.59 and 15.47 kJ mol(-1) within the temperature range of 300 to 400 K. Xylene density profiles and orientational analysis suggested that this can be attributed to the xylene molecules that diffuse in the FAU zeolite by two different mechanisms at high and low temperatures. The behavior of motion for xylene in the FAU zeolite exhibits a "fluid-like" mode at high temperatures and exhibits a "jump-like" mode at low temperatures.     

Measurement of the adduction constant by gas-liquid chromatography

Summary The adduction constants for the following eight binary systems were measured by gas liquid chromatography, at different temperatures: tetrachloromethane/p-xylene, tetrachloromethane/pseudocumene, chloroform/p-xylene, chloroform/pseudocumene, chloroform/aniline, m-methylphenol/aniline, o-methylphenol/aniline, and o-chlorophenol/aniline. The relationships between the adduction constant and temperature were used to fit the enthalpies and entropies of adduct formation.     

100 selective oxygenation of p-xylene to p-tolualdehyde via photoinduced electron transfer

The 100% selective oxygenation of p-xylene to p-tolualdehyde is initiated by photoinduced electron transfer from p-xylene to the singlet excited state of 10-methyl-9-phenylacridinium ion under visible light irradiation, yielding p-tolualdehyde exclusively as the final oxygenated product. The reason for the high selectivity in the photocatalytic oxygenation of p-xylene is discussed on the basis of the photoinduced electron transfer mechanism.     

甘油催化氢解的研究与应用

近年来由于生物柴油产业的快速发展,甘油作为其生产过程中的副产品大量生成,合理利用这些过剩的甘油将有助于增加整个生物柴油产业的经济效益。本文对近年来利用甘油为原料催化氢解合成二元醇（1,2-丙二醇、1,3-丙二醇和乙二醇）的研究进展进行了综述,介绍了甘油催化氢解的研究背景,着重讨论了甘油催化氢解生成二元醇的反应机理（包括脱水-加氢机理、脱氢-加氢机理和螯合机理）和甘油催化氢解在生产二元醇上的应用,并对甘油催化氢解的发展前景做了展望。     

Effect of preadsorbed water on the adsorption of p-xylene and m-xylene mixtures on BaX and BaY zeolites

Adsorption of an equimolar p-xylene/m-xylene mixture on partially hydrated barium-exchanged X and Y zeolites is studied at 423 K in the pressure range 10(-2)-8 hPa by differential calorimetry coupled with manometry and chromatography. Results are consistent with structural studies and Monte Carlo simulations of the literature. The presence of preadsorbed water in supercages increases the adsorption selectivity toward p-xylene to the detriment of the adsorption capacity and the adsorption affinity, as indicated by a sharp decrease of the Henry constants. However, the coadsorption heats at zero filling are not influenced by the presence of water. Therefore, entropic effects seem to play an important role in the coadsorption process. Two adsorption sites whose energy differs are identified by calorimetry. The more energetic site could correspond to the p-xylene or m-xylene molecule in interaction with the compensation cation located in sites II in the supercage, the less energetic to the adsorption of p-xylene molecule in the 12-ring window joining two supercages. The presence of this second site for p-xylene could be at the origin of the selectivity.     

Energy transfer between polyatomic molecules II: Energy transfer quantities and probability density functions in benzene, toluene, p-xylene, and azulene collisions

Collisional energy transfer, CET, is of major importance in chemical, photochemical, and photophysical processes in the gas phase. In Paper I of this series (J. Phys. Chem. B 2005, 109, 8310) we have reported on the mechanism and quantities of CET between an excited benzene and cold benzene and Ar bath. In the present work, we report on CET between excited toluene, p-xylene, and azulene with cold benzene and Ar and on CET of excited benzene with cold toluene, p-xylene, and azulene. We compare our results with those of Paper I and report average vibrational, rotational, and translational energy quantities, , transferred in a single collision. We discuss the effect of internal rotation on CET and the identity of the gateway modes in CET and the relative role of vibrational, rotational, and translational energies in the CET process, all that as a function of temperature and excitation energy. Energy transfer probability density functions, P(E,E'), for the various systems are reported and the shape of the curves for various systems and initial conditions is discussed. The major findings for polyatomic-polyatomic collisions are: CET takes place mainly via vibration-to-vibration energy transfer assisted by overall rotations. Internal free rotors in the excited molecule hinder energy exchange while in the bath molecule they do not. Energy transfer at low temperatures and high temperatures is more efficient than that at intermediate temperatures. Low-frequency modes are the gateway modes for energy transfer. Vibrational temperatures affect energy transfer. The CET probability density function, P(E,E'), is convex at low temperatures and can be concave at high temperatures. A mechanism that explains the high values of and the convex shape of P(E,E') is that in addition to short impulsive collisions there are chattering collisions where energy is transferred in a sequence of short encounters during the lifetime of the collision complex. This also leads to the observed supercollision tail at the down wing of P(E,E'). Polyatomic-Ar collisions show mechanistic similarities to polyatomic-polyatomic collisions, but there are also many dissimilarities: internal rotations do not inhibit energy transfer, P(E,E') is concave at all temperatures, and there is no contribution of chattering collisions.     

Energy transfer between polyatomic molecules. 3. Energy transfer quantities and probability density functions in self-collisions of benzene, toluene, p-xylene and azulene

This paper is the third and last in a series of papers that deal with collisional energy transfer, CET, between aromatic polyatomic molecules. Paper 1 of this series (J. Phys. Chem. B 2005, 109, 8310) reports on the mechanism and quantities of CET between an excited benzene and cold benzene and Ar bath. Paper 2 in the series (J. Phys. Chem., in press) discusses CET between excited toluene, p-xylene and azulene with cold benzene and Ar and CET between excited benzene colliding with cold toluene, p-xylene and azulene. The present work reports on CET in self-collisions of benzene, toluene, p-xylene and azulene. Two modes of excitation are considered, identical excitation energies and identical vibrational temperatures for all four molecules. It compares the present results with those of papers 1 and 2 and reports new findings on average vibrational, rotational, and translational energy, , transferred in a single collision. CET takes place mainly via vibration to vibration energy transfer. The effect of internal rotors on CET is discussed and CET quantities are reported as a function of temperature and excitation energy. It is found that the temperature dependence of CET quantities is unexpected, resembling a parabolic function. The density of vibrational states is reported and its effect on CET is discussed. Energy transfer probability density functions, P(E,E'), for various collision pairs are reported and it is shown that the shape of the curves is convex at low temperatures and can be concave at high temperatures. There is a large supercollision tail at the down wing of P(E,E'). The mechanisms of CET are short, impulsive collisions and long-lived chattering collisions where energy is transferred in a sequence of short internal encounters during the lifetime of the collision complex. The collision complex lifetimes as a function of temperature are reported. It is shown that dynamical effects control CET. A comparison is made with experimental results and it is shown that good agreement is obtained.     

Vapor-liquid equilibria for binary mixtures of carbon dioxide with benzene,toluene and p-xylene

Vapor-liquid equilibrium data for carbon dioxide - benzene, carbon dioxide - toluene, and carbon dioxide - p-xylene were measured for pressures up to 6.5 MPa, and at temperatures of 353 K, 373 K, and 393 K. The solubility of benzene in the dense carbon dioxide vapor phase is higher than that of either toluene or p-xylene. In the liquid phase, carbon dioxide is more soluble in p-xylene than in toluene or benzene. The experimental data obtained were compared with calculations from three correlations: the Peng-Robinson equation, the UNIFAC activity coefficient correlation, and the Perturbed-Anisotropic- Chain Theory (PACT). All three correlations predict phase compositions in good agreement with the experimental data.     

苯乙烯与邻、间、对-二甲苯二元混合液的分子间相互作用

The densities (ρ), ultrasonic speeds (v), and refractive indices (n) of binary mixtures of styrene (STY)with m-, o-, or p-xylene, including those of their pure liquids, were measured over the entire composition range at the temperatures 298.15, 303.15, 308.15, and 313.15 K. The excess volumes (VE), deviations in isentropic compressibilities(△ks), acoustic impedances (△Z), and refractive indices (△n) were calculated from the experimental data. Partial molar volumes (V0φ,2) and partial molar isentropic compressibilities (K0φ,2) of xylenes in styrene have also been calculated. The derived functions, namely, VE, △ks, △Z, △n, V0φ,2, and K0φ,2 were used to have a better understanding of the intermolecular interactions occurring between the component molecules of the present liquid mixtures. The variations of these parameters suggest that the interactions between styrene and o-, m-, or p-xylene molecules follow the sequences: p-xylene＞o-xylene＞m-xylene. Apart from using density data for the calculation of VE, excess molar volumes were also estimated using refractive index data. Furthermore, several refractive index mixing rules have been used to estimate the refractive indices of the studied liquid mixtures theoretically. Overall, the computed and measured data were interpreted in terms of interactions between the mixing components.     

Role of Re Species and Acid Cocatalyst on Ir‐ReOx/SiO2 in the C–O Hydrogenolysis of Biomass‐Derived Substrates

The catalytic performance of ReO_x‐modified Ir metal catalyst in the hydrogenolysis of C–O bonds is strongly dependent on the choice of solvent. The acidic property of the Re species becomes obvious in the alkane solvent, and the hydrogenolysis reaction proceeds mainly by acid‐catalyzed dehydration and the subsequent metal‐catalyzed hydrogenation. The acidic property of the Re species is weakened in water; however, the hydrogenolysis reaction proceeds in water via a direct mechanism involving S_N2‐like attack of a hydride species at the interface between Ir and ReO_x on the adsorbed Re alkoxide species. This mechanism enabled the selective dissociation of the C–O bond neighboring the CH₂OH group.     

Kinetics and Mechanism of the Heterogeneous Catalytic Hydrogenolysis of Chlorobenzenes and Chlorocyclohexanes

The catalytic hydrogenolysis of hexachlorobenzene and hexachlorocyclohexanes (isomer mixture) on a nickel–chromia catalyst and hexachlorobenzene hydrogenolysis intermediates (1,2,4,5-tetrachlorobenzene, 1,2,4-trichlorobenzene, 1,2-dichlorobenzene, and chlorobenzene) are studied. The hydrogenation of an aromatic ring does not occur in the presence of chemisorbed chlorine atoms on the catalyst surface. A reaction mechanism for chlorobenzene hydrogenation was proposed taking into account experimental evidence that, in the presence of chemisorbed chlorine on the catalyst surface, hydrogen in a dissociated state is firmly bound to the surface. It is found that the desorption of the resulting hydrogen chloride is the slowest step in chlorobenzene hydrogenolysis. The hydrogenolysis of hexachlorocyclohexanes occurs via a dehydrochlorination stage with the formation of trichlorobenzenes, which are subsequently converted into chlorobenzene and benzene.     

Facile synthesis of hypercrosslinked resin via photochlorination of p-xylene and succedent alkylation polymerization

A combination of photochlorination of p-xylene and succedent Friedel-Crafts alkylation polymerization was firstly used in the preparation of the hypercrosslinked adsorptive resin.The data of GC-MS and GC showed that a series of chlorizates were produced when p-xylene was photochlorinated.Hypercrosslinked resins could be synthesized by copolymerization,self-polymerization of chlorizates or post crosslinking reaction.The chemical structure and micromorphology of the porous resins were characterized by BET,FT-IR,SEM and elementary analysis(EA).The results showed that the novel adsorptive resins possess high BET surface near to 1038 m~2/g and large pore volumes range from 0.5 to 1.2 cm~3/g.     

Hydrogenolysis of carbon-fluorine bonds in catalytic hydrogenation

In contrast to the strong stability of saturated fluorine compounds in catalytic hydrogenation, allylic and vinylic fluorine atoms are displace by hydrogen relatively readily. Hydrogenolysis of carbon-fluorine bonds accompanies addition of hydrogen across double bonds in methyl 4-fluoro-3-methyl-2-pentenoate, in fluoromaleic, fluorofumaric, difluoromaleic and difluorofumaric acids. The extent of hydrogenolysis is affected by the catalyst and by the solvent. A concerted mechanism is offered to explain the readiness of the hydrogenolysis in allylic and vinylic fluorides.     

Hole tunneling and hopping in a Ru(bpy)3(2+)-phenothiazine dyad with a bridge derived from oligo-p-phenylene

A molecular dyad was synthesized in which a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) photosensitizer and a phenothiazine redox partner are bridged by a sequence of tetramethoxybenzene, p-dimethoxybenzene, and p-xylene units. Hole transfer from the oxidized metal complex to the phenothiazine was triggered using a flash-quench technique and investigated by transient absorption spectroscopy. Optical spectroscopic and electrochemical experiments performed on a suitable reference molecule in addition to the above-mentioned dyad lead to the conclusion that hole transfer from Ru(bpy)(3)(3+) to phenothiazine proceeds through a sequence of hopping and tunneling steps: Initial hole hopping from Ru(bpy)(3)(3+) to the easily oxidizable tetramethoxybenzene unit is followed by tunneling through the barrier imposed by the p-dimethoxybenzene and p-xylene spacers. The overall charge transfer proceeds with a time constant of 41 ns, which compares favorably to a time constant of 1835 ns associated with equidistant hole tunneling between the same donor-acceptor couple bridged by three identical p-xylene units. The combined hopping/tunneling sequence thus leads to an acceleration of hole transfer by roughly a factor of 50 when compared to a pure tunneling mechanism.     

Toluene Alkylation to Selective Formation of p-Xylene over Co-Crystalline ZSM-12/ZSM-5 Catalyst

The alkylation of toluene with methanol to selective formation of p-xylene has been systematically studied. ZSM-12 (MTW)/ZSM-5 co-crystalline zeolite in 40:60 proportions have been synthesized by the same molar gel composition, but at different temperatures and periods than that of ZSM-12 and ZSM-5, separately. All the prepared samples are characterized by XRD, SEM, BET, and XRF. The activity of toluene alkylation was investigated with a mixture of toluene and methanol as a feed over the ZSM-12, ZSM-12/ZSM-5 co-crystalline, ZSM-5, and physical mixture of ZSM-12/ZSM-5. Prom characterization, it is observed that the ZSM-12/ZSM-5 co-crystalline material is different from that of ZSM-12, ZSM-5, and their physical mixture. Further, the ZSM-12/ZSM-5 co-crystalline zeolite produces the highest content of xylene and has better selectivity for p-xylene than ZSM-12, ZSM-5, and their physical mixture.     

Determination of thermodynamic properties of isotactic poly(1-butene) at infinite dilution using density and inverse gas chromatography

The partial molar volumes, V1(M), and the molar volume of isotactic crystalline low-molecular-weight poly(1-butene), iPBu-1, V1, have been calculated from the measured density of {iPBu-1 + solvent (n-hexane, n-heptane, n-nonane, n-decane, p-xylene, cyclohexane and chloroform)} systems. Some of the thermodynamic quantities were also obtained for the iPBu-1 with eight hydrocarbons (n-octane, n-decane, n-undecane, n-dodecane, n-tridecane, o-xylene, m-xylene, p-xylene) by the method of inverse gas chromatography at various temperatures. The weight fraction activity coefficients of the solvent at infinite dilution, omega2(infinity) and the Flory-Huggins thermodynamic interaction parameters, chi21(infinity), between polymer and solvents were determined. The partial molar free energy, deltaG2(infinity), the partial molar heat of mixing, deltaH2(infinity), at infinite dilution and the polymer solubility parameter, delta1, were calculated. Additionally, the (solid + liquid) binary mixtures equilibria, SLE, of iPBu-1 with three hydrocarbons (n-octane, n-decane and m-xylene) were studied by a dynamic method. By performing these experiments over a large concentration range, the T-x phase diagrams of the polymer-solvent systems were constructed. The excess Gibbs energy models were used to describe the nonideal behaviour of the liquid phase. The omega2(infinity) were determined from the solubility measurements and were predicted by using the UNIFAC FV model.     

Nickel-mediated hydrogenolysis of C-O bonds of aryl ethers: what is the source of the hydrogen?

Mechanistic studies of the hydrogenolysis of aryl ethers by nickel were undertaken with (diphosphine)aryl methyl ethers. A Ni(0) complex containing Ni-arene interactions adjacent to the aryl-O bond was isolated. Heating led to aryl-O bond activation and generation of a nickel aryl methoxide complex. Formal β-H elimination from this species produced a nickel aryl hydride which can undergo reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). The reported complexes map out a plausible mechanism of aryl ether hydrogenolysis catalyzed by nickel. Investigations of a previously reported catalytic system using isotopically labeled substrates are consistent with the mechanism proposed in the stoichiometric system, involving β-H elimination from a nickel alkoxide rather than cleavage of the Ni-O bond by H(2).     

Variation of excess volumes with temperature for binary mixtures ofp-xylene withn-hexane andn-hexadecane

The variation of the molar volume with temperature from 25 to 50 °C of binary mixtures of p-xylene + n-hexane and p-xylene + n-hexadecane has been measured by a dilatometric method over the complete mole fraction range. From the experimental results we have calculated v^E/T)_p. Literature values of v^E at 25°C together with the integration of v^E/T)_p yield v^E as a function of temperature. The excess volumes of p-xylene + n-hexane at 40 °C and p-xylene + n-hexadecane at 40 and 45 °C have also been measured by a dilatometric method, and the results were compared to those obtained from the integration of . The results from both methods are in excellent agreement within experimental error.The experimental values of are negative for the system p-xylene + n-hexane and positive for p-xylene + n-hexadecane. We have interpreted our experimental results in terms of the order present in p-xylene and n-alkanes.     

对二甲苯＋环己烷及对二甲苯＋二甲基亚砜的固液相平衡和过量吉布斯自由能

测定了对二甲苯＋环己烷及对二甲苯＋二甲基亚砜体系（均为简单低共熔混合物）的固液平衡相图，计算出它们在３１３．１５Ｋ的过量吉布斯自由能。结果表明两体系对理想溶液均产生正偏差。     

Solid state NMR method for the determination of 3D zeolite framework/sorbate structures: 1H/29Si CP MAS NMR study of the high-loaded form of p-xylene in ZSM-5 and determination of the unknown structure of the low-loaded form

A general protocol is described for structure determinations of organic sorbate-zeolite complexes based on the selective, through-space, distance-dependent transfer of magnetization from protons in selectively deuterated organics to framework silicon nuclei. The method was developed using the known structure of the high-loaded ZSM-5/p-xylene complex containing p-xylene-d(6) or p-xylene-d(4). It was then applied to determine the unknown structure of the low-loaded ZSM-5/p-xylene complex using NMR alone. For the high-loaded complex improved data were obtained below 273 K, where slow motions and exchange processes of the p-xylene are eliminated. The general approach was validated by the exact agreement of the experimental (1)H-(29)Si CPMAS spectra obtained at a specific contact time and the complete 24-line spectra simulated using 1/T(CP) vs M(2) correlations from only the six clearly resolved resonances. For the low-loaded complex the (29)Si resonances were assigned at 267 K, and variable contact time CP experiments were carried out between 243 and 173 K using the same specifically deuterated p-xylenes. All possible locations and orientations of the p-xylene guests were sampled, and those solutions that gave acceptable linear 1/T(CP) vs M(2) correlations were selected. The optimum p-xylene location in this temperature range was determined to be in the channel intersection with the long molecular axis parallel to [0,1,0] (ring center fractional coordinates {-0.009, 0.250, 0.541}) with the ring plane oriented at an angle of 30 +/- 3 degrees about the crystallographic b axis. A subsequent single-crystal X-ray study confirmed this predicted structure.