Formation Of Toluene Research Articles

Synthesis and Photophysical Behavior of Two Novel Bis(1,8-naphthalimides) Containing Triazine Spacers

以1,8-萘酰亚胺和三聚氯氰为主要原料, 合成了两种由三嗪环桥连的双1,8-萘酰亚胺化合物3 和5. 采用紫外-可见光谱和荧光光谱等手段考察了两种化合物在不同溶剂中的光物理行为. 与参比化合物N-丁基-1,8-萘酰亚胺相比, 在二氯甲烷、三氯甲烷和甲醇等极性溶剂中, 化合物3和5除了在短波区（λ〈400 nm）存在1,8-萘酰亚胺的特征荧光发射峰外, 在长波区（〉450 nm）均产生一个较强的新荧光发射峰, 表现出分子内激基缔合物的光物理行为. 与化合物5相比, 由于化合物3特殊的构象异构, 其荧光强度发生严重的猝灭. 在非极性溶剂甲基环己烷中, 化合物5 由于存在较强的分子间氢键作用而聚集, 受激后形成了较稳定的分子间激基缔合物, 但未观察到明显的分子内激基缔合物的形成. 在甲苯溶剂中, 化合物3和5与甲苯分子形成了激基复合物, 并未形成分子内激基缔合物. 进一步研究3和5的固态激发态性质, 发现化合物3和5的固体薄膜受激后分别在465和469 nm处出现激基缔合物的特征荧光发射峰.

Bimetallic effects in the hydrodeoxygenation of meta-cresol on γ-Al2O3 supported Pt–Ni and Pt–Co catalysts

The hydrodeoxygenation (HDO) of meta-cresol, a typical phenolic compound in bio-oils, is investigated in the vapor-phase on γ-Al2O3-supported Pt catalysts at near atmospheric hydrogen pressure. The HDO reaction yields two major hydrocarbons: toluene and methylcyclohexane. The deoxygenation of meta-cresol proceeds through two consecutive steps: hydrogenation of the aromatic ring on the Pt metal followed by dehydration reactions of the produced alcohol intermediates on the alumina support. Phenolic ring saturation is proposed to be slower than its sequential dehydration steps on Pt/γ-Al2O3. This is in a good agreement with the higher selectivity of toluene compared to that of the hydrogenated cyclic hydrocarbon, methylcyclohexane, because toluene formation requires fewer ring hydrogenation steps than its counterpart. The additions of Co and Ni into Pt not only improve the overall HDO conversion, but also modify the product distribution. The enhancement in the overall HDO activity is related to the better hydrogenation activity of bimetallic Pt–Co and Pt–Ni catalysts and the generation of additional sites for alcohol dehydration. Consequently, more saturated cyclic hydrocarbon product, methylcyclohexane, is observed on bimetallic catalysts with respect to the monometallic Pt catalyst.

Chemical Structures of Low-Pressure Premixed Methylcyclohexane Flames as Benchmarks for the Development of a Predictive Combustion Chemistry Model

The chemical compositions of three low-pressure premixed flames of methylcyclohexane (MCH) are investigated with the emphasis on the chemistry of MCH decomposition and the formation of aromatic species, including benzene and toluene. The flames are stabilized on a flat-flame (McKenna type) burner at equivalence ratios of φ = 1.0, 1.75, and 1.9 and at low pressures between 15 Torr (= 20 mbar) and 30 Torr (= 40 mbar). The complex chemistry of MCH consumption is illustrated in the experimental identification of several C7H12, C7H10, C6H12, and C6H10 isomers sampled from the flames as a function of distance from the burner. Three initiation steps for MCH consumption are discussed: ring-opening to heptenes and methyl-hexenes (isomerization), methyl radical loss yielding the cyclohexyl radical (dissociation), and H abstraction from MCH. Mole fraction profiles as a function of distance from the burner for the C7 species supplemented by theoretical calculations are presented, indicating that flame structures resulting in steeper temperature gradients and/or greater peak temperatures can lead to a relative increase in MCH consumption through the dissociation and isomerization channels. Trends observed among the stable C6 species as well as 1,3-pentadiene and isoprene also support this conclusion. Relatively large amounts of toluene and benzene are observed in the experiments, illustrating the importance of sequential H-abstraction steps from MCH to toluene and from cyclohexyl to benzene. Modeled results using the detailed chemical model of Pitz et al. (Proc. Combust. Inst.2007, 31, 267–275) are also provided to illustrate the use of these data as a benchmark for the improvement or future development of a MCH mechanism.

Bifunctional transalkylation and hydrodeoxygenation of anisole over a Pt/HBeta catalyst

The catalytic conversion of anisole (methoxybenzene), a phenolic model compound representing a thermal conversion product of biomass lignin, to gasoline-range molecules has been investigated over a bifunctional Pt/HBeta catalyst at 400 °C and atmospheric pressure. The product distribution obtained on the bifunctional catalyst was compared with those obtained on monofunctional catalysts (HBeta and Pt/SiO 2). This comparison indicates that the acidic function (HBeta) catalyzes the methyl transfer reaction (transalkylation) from methoxyl to the phenolic ring, yielding phenol, cresols, and xylenols as the major products. The metal function catalyzes demethylation, hydrodeoxygenation, and hydrogenation in sequence, resulting in phenol, benzene, and cyclohexane. On the bifunctional catalyst, both methyl transfer and hydrodeoxygenation are achieved at significantly higher rates than over the monofunctional catalysts, leading to the formation of benzene, toluene, and xylenes with lower hydrogen consumption and a significant reduction in carbon losses, in comparison with the metal function alone. In addition, on the bifunctional Pt/HBeta, the rate of deactivation and coke deposition are moderately reduced.

Controlling the Duality of the Mechanism in Liquid‐Phase Oxidation of Benzyl Alcohol Catalysed by Supported Au–Pd Nanoparticles

In the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O(2), whereas the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation. It has been observed that the presence of O(2) increases the turnover number of this disproportionation reaction as compared to reactions in a helium atmosphere, implying that there are two catalytic pathways leading to toluene.

ChemInform Abstract: Physicochemical and Catalytic Properties of a Silica-Enriched Zeolite ZSM-20

Zeolite ZSM-20 with and enhanced Si : Al ratio after activation has been obtained by a modification of the usual synthesis route. Despite the increased silica content the crystallinity is high and the crystal structure is nearly identical to that of the ZSM-20 zeolites reported so far. The synthesis was found to be extremely sensitive to the conditions of gel preparation, especially to pH adjustment, the temperature–time regime for hydrolysis of the organic silica source, the evaporation of the released ethanol and the formation of the silica precursors. The well crystallized synthesis product was characterized by X-ray powder diffraction, infrared spectroscopy, thermal analysis, n-hexane adsorption and temperature-programmed desorption of ammonia. The acidity of this ZSM-20 zeolite is high compared with conventional preparations of ZSM-20 zeolites or with the structurally related zeolite Y.The catalytic properties in the isomerization of m-xylene and the conversion of ethylbenzene have been studied. The isomerization of m-xylene is characterized by a high percentage of disproportionation (toluene formation) due to the high acidity. The distribution of the trimethylbenzene isomers corresponds to the thermodynamic equilibrium. Shape selectivity is obviously not operative owing to the open pore structure. Ethylbenzene is mainly dealkylated to benzene where the new ZSM-20 zeolite is capable of breaking the ethyl side chain to yield toluene.

On-off QD switch that memorizes past recovery from quenching by diazonium salts

The understanding of the interaction of CdSe/ZnS semiconductor quantum dots (QD) with their chemical environment is fundamental, yet far from being fully understood. p-Methylphenyldiazonium tetrafluoroborate has been used to get some insight into the effect of diazonium salts on the spectroscopy of QD. Our study reveals that the surface of CdSe/ZnS quantum dots can be modified by diazonium salts (although not functionalized), showing and on-off fluorescence behaviour that memorizes past quenching recoveries. Facile modification of the surface confers protection against quenching by new molecules of diazonium salt and other known quenchers such as 4-amino-TEMPO. The reaction mechanism has been explored in detail by using different spectroscopic techniques. At the first time after addition of diazonium salt over QD the fluorescent is turned off with Stern-Volmer behaviour; the fluorescence recovers following irradiation. Subsequent additions of diazonium salts do not cause the same degree of quenching. We have noted that the third addition (following two cycles of addition and irradiation) is unable to quench the fluorescence. Monitoring the process using NMR techniques reveals the formation of p-difluoroborane toluene as a result of the irradiation of diazonium-treated QD; the treatment leads to the fluorination of the QD surface.

Unusual Reactivity of a Tm-Pyrrolide/Aluminate Complex with a Metallocene-Type Structural Motif

Reaction of in situ generated (Me4Al)3Tm with 2,3,4,5-tetramethylpyrrole afforded Tm(Me){μ-CH2AlMe2(η5-NC4Me4)]2} (1), containing a terminally bonded CH3 group. The two pyrrolide rings confer the bent-metallocenic motif to the lanthanide by adopting a fairly symmetrical π-bonding mode. Each of the N atoms of the pyrrolide rings is bonded to one AlMe2 residue, which in turn bridges the lanthanide through a CH2 unit of an Al2(μ-CH2)Tm moiety. The reactivity of the terminal Me group of 1 was examined with both H2 and PhSiH3. Reaction with H2 under high pressure and room temperature caused loss of the terminal methyl group and major redistribution of the pyrrolyl moieties, yielding Tm[AlMe2(η5-NC4Me4)2][(μ-Me)(AlMe2)][(μ3-CH2)(AlMe3)] (2), with a stable ansa-metallocene type of structure and intacting Al2(μ-CH2)Tm unit. Reaction of 1 with PhSiH3 under mild conditions afforded an even more complex transformation accompanied by evolution of CH4 and formation of toluene. The resulting Tm[AlMe2(η5-NC4Me4)2](AlMe3...

Theoretical calculations of the kinetics and mechanisms of the gas phase elimination of primary, secondary, and tertiary 2‐hydroxyalkylbenzenes

AbstractTheoretical study of the elimination kinetics of 2‐phenylethanol, 1‐phenyl‐2‐propanol, and 2‐methyl‐1‐phenyl‐2‐propanol in the gas‐phase has been carried out at the MP2/6‐31G(d,p), B3LYP/6‐31G(d,p), B3LYP/6‐31++G(d,p), MPW1PW91/6‐31G(d,p), MPW1PW91/6‐31++G(d,p), PBEPBE/6‐31G(d,p), and PBEPBE/6‐31++G(d,p) levels of theory. The three substrates undergo two parallel elimination reactions. The first elimination appears to proceed through a six‐membered cyclic transition state to give toluene and the corresponding aldehyde or ketone. The second parallel elimination takes place through a four‐membered cyclic transition state producing water and the corresponding unsaturated aromatic hydrocarbon. Results from MP2/6‐31G(d,p) and MPW1PW91/6‐31++G(d,p) methods were found to be in good agreement with the experimental kinetic and thermodynamic parameters in the formation of toluene and the corresponding carbonyl compound. However, the results for PBEPBE/6‐31G(d,p) were in better agreement with the experimental data for the second parallel reaction yielding water and the corresponding unsaturated aromatic hydrocarbon. The charge distribution differences in the TS related to the substitution by methyl groups in the substrates can account for the observed reaction rate coefficients. The synchronicity parameters imply semi‐polar transition states for these elimination reactions. Copyright © 2009 John Wiley & Sons, Ltd.

Effect of alkali species on performance of MnO/γ-Al2O3 catalysts for the hydrogenation of methyl benzoate to benzaldehyde

Abstract The effect of alkali species on performance of MnO/γ-Al 2 O 3 catalysts for methyl benzoate hydrogenation was investigated in fixed-bed reactor. Doping alkali species on MnO/γ-Al 2 O 3 catalysts enhanced the selectivity of benzaldehyde significantly, toluene and benzyl methyl ether were greatly suppressed. The infrared spectra of adsorbed pyridine adsorption was acquired to study the surface acid properties, the results revealed that doping alkali species weakened the acid strength of MnO/γ-Al 2 O 3 catalysts, which lead to restrain from the formation of toluene and benzyl methyl ether.

Can Toluene or Xylene Form Clathrate Hydrates?

In this communication, we examine the possibility of clathrate hydrate formation of toluene and o-, m-, or p-xylene with methane as help gas. An isochoric pressure-search method was used to measure hydrate phase equilibrium boundaries. The reliability of this method is tested by generating hydrate phase equilibrium boundary data for the methane−benzene−water system and comparing them with experimental data reported in the literature. The acceptable agreements demonstrate the reliability of the technique used in this work. The new experimental data of hydrate phase equilibrium boundary for the methane−(toluene/(o/m/p)-xylene)−water systems are compared with some selected experimental data from the literature for the methane−water system to study the possibility of shifting the hydrate phase equilibrium boundary of the latter system by the presence of toluene and o-, m-, or p-xylene. It is shown that toluene and o-, m-, or p-xylene have little or almost no effect on the hydrate phase equilibrium boundary of...

A comparative study of the formation of aromatics in rich methane flames doped by unsaturated compounds

For a better modeling of the importance of the different channels leading to the first aromatic ring, we have compared the structures of laminar rich premixed methane flames doped with several unsaturated hydrocarbons: allene and propyne, because they are precursors of propargyl radicals which are well known as having an important role in forming benzene, 1,3-butadiene to put in evidence a possible production of benzene due to reactions of C 4 compounds, and, finally, cyclopentene which is a source of cyclopentadienyl methylene radicals which in turn are expected to easily isomerizes to give benzene. These flames have been stabilized on a burner at a pressure of 6.7 kPa (50 Torr) using argon as dilutant, for equivalence ratios ( ϕ) from 1.55 to 1.79. A unique mechanism, including the formation and decomposition of benzene and toluene, has been used to model the oxidation of allene, propyne, 1,3-butadiene and cyclopentene. The main reaction pathways of aromatics formation have been derived from reaction rate and sensitivity analyses and have been compared for the three types of additives. These combined analyses and comparisons can only been performed when a unique mechanism is available for all the studied additives.

Selective and stable benzene alkylation with methane into toluene over PtH-MFI bifunctional catalyst

This paper demonstrates for the first time that methane reacts with benzene over bifunctional PtH-MFI catalyst with selective and stable formation of toluene at such low temperature as 370 °C. Our results show that the catalyst activity increases during the initial period of the reaction (∼4 h) and that this increase is likely associated with the modification of the Pt particles with the surface carbonaceous species (e.g. CH 3, CH 2, CH, C, and C 2H x ). The highest catalyst activity is observed at time on stream (TOS) of 4 h, when toluene selectivity is around 96 mol% and conversions of benzene (4.5%) and methane (0.53%) are close to the equilibrium conversions (5.6% and 0.62% for benzene and methane, respectively). At higher TOS, the catalyst activity declines slowly and at TOS of 23 h conversions of benzene and methane are around 3.8% and 0.45%, respectively. To the best of our knowledge, the reaction of benzene alkylation with methane into toluene, reported in this paper, is the first example of the catalytic reaction involving methane that proceeds continuously during many hours under non-oxidizing conditions.

Dimethyl Ether as a Source of Reactive Species for Alkylation of Benzene

The co-reaction of dimethyl ether and benzene has been investigated on pure and promoted-ZSM-5 catalysts at 473–773 K. It was found that the addition of benzene to dimethyl ether markedly increased the formation of toluene, xylene and C9 aromatics on ZSM-5 at and above 623 K. This feature is attributed to the reaction of benzene with the reactive hydrocarbon species formed in the decomposition of dimethyl ether on the acidic sites of ZSM-5 zeolite. The extent of the enhancement was further increased by ZnO and Mo2C promoters.

Study of n-octene aromatization over nanoscale HZSM-5 zeolite

Influence of space velocity and acidity of HZSM-5 zeolite on the aromatization of n-octene over nanoscale HZSM-5 has been investigated at 350 and 400 °C. The distribution of aromatics is strongly influenced by the space velocity and the amount of the strong acid sites of the catalyst. The results show toluene and C 8 aromatics are the most significant aromatics products while the formation of benzene is less rapid during the aromatization of n-octene over the nanoscale HZSM-5 zeolite. Due to the high steric hindrance in the ZSM-5 channels, C 9 aromatics are formed in the external surface of the nanoscale HZSM-5 zeolite. With the decrease of the space velocity, the selectivities of benzene and toluene increase while those of C 8 and C 9 aromatics decrease. The decrease of the amount of the strong acid sites results in the decrease of the concentrations of C 6 and C 7 carbenium ions and the increase of those of C 8 and C 9 carbenium ions. Consequently, the decrease of the amount of the strong acid sites leads to the decrease in the formation of benzene and toluene and the increase in that of C 8 and C 9 aromatics.

Thermal Chemistry of 1-Methyl-1-cyclohexene and Methylene Cyclohexane on Pt(111) Single-Crystal Surfaces

The reactivity of 1-methyl-1-cyclohexene (1MC6=) and methylene cyclohexane (MeC6) on a Pt(111) single-crystal surface was investigated by means of temperature-programmed desorption (TPD) and reflection−absorption infrared spectroscopy (RAIRS). Dehydrogenation of both compounds occurs via the formation of a common 1-methyl cyclohexenyl species, as corroborated by supporting data from cyclohexene dehydrogenation and 3-bromo cyclohexene thermal activation on Pt(111), and leads to the ultimate formation of toluene, which desorbs at 430 K. On the other hand, hydrogenation, isomerization, and H−D exchange reactions all take place by following the so-called Horiuti−Polanyi mechanism and involve a common 1-methyl cyclohexyl surface intermediate. 1MC6= and MeC6 display different reactivities, with MeC6 isomerizing to 1MC6=, but both hydrogenate to methyl cyclohexane (MC6). These reactions are enhanced by the presence of predosed hydrogen on the surface and undergo extensive early H−D exchange if deuterium is used instead.

Surface modification of nano-sized HZSM-5 and HFER by pre-coking and silanization

Deposition of carbonaceous and siliceous materials was used to enhance the selectivity of HZSM-5 and HFER by passivating non-selective acid sites present on the external surface of zeolite crystallites. The nature of carbonaceous deposits formed during the pre-coking treatment was studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) after zeolite dissolution by hydrofluoric acid. Molecular weights up to 1300 Da were observed for coke species present on the pre-coked HZSM-5 sample to which carbon numbers nC∼100 can be assigned. In terms of inactivation of surface acidity, samples modified by pre-coking were found to be more effective compared to those by one-cycle silica deposition, as evidenced by 31P MAS NMR of adsorbed tributylphosphine oxide as the probe molecule. Accordingly, pre-coked HZSM-5 yielded a higher shape selectivity during xylene isomerization, i.e., a reduced formation of undesirable toluene and trimethylbenzenes. For skeletal isomerization of n-butene on HFER, silanization caused a decrease in isobutene formation due to the deposition of siliceous materials within the channels. Pre-coking of HFER showed no specific effect on isobutene selectivity and, accordingly, these polyaromatic carbonaceous deposits cannot be assigned to specific catalytic sites.

Rich methane premixed laminar flames doped by light unsaturated hydrocarbons: III. Cyclopentene

In line with the studies presented in Parts I (methane flame seeded with allene and propyne) and II (methane flame seeded with 1,3-butadiene) of this paper, the structure of a laminar rich premixed methane flame doped with cyclopentene has been investigated. The gases of this flame contain 15.3% (molar) of methane, 26.7% of oxygen, and 2.4% cyclopentene, corresponding to an overall equivalence ratio of 1.79 and a C 5H 8/CH 4 ratio of 15.7%. The flame has been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 36 cm/s at 333 K. The measured temperature ranged from 627 K close to the burner up to 2027 K. Species quantified by gas chromatography included the usual methane C 0–C 2 combustion products, but also propyne, allene, propene, propane, 1-butene, 1,3-butadiene, 1,2-butadiene, vinylacetylene, diacetylene, cyclopentadiene, 1,3-pentadiene, benzene, and toluene. A new mechanism for the oxidation of cyclopentene has been developed and added to the former model for the oxidation of small unsaturated hydrocarbons, benzene, and toluene described in Parts I and II. The whole mechanism involved 175 species in 1134 reactions. The main reaction pathways of consumption of cyclopentene and of formation of benzene and toluene are presented and discussed from flow rate analyses.

Application of nano-nickel catalyst in the viscosity reduction of Liaohe extra-heavy oil by aqua-thermolysis

Nano-nickel catalyst was prepared in methylcyclohexane-water-n-octanol-AEO 9 micro-emulsion system, and used in the viscosity reduction process of Liaohe extra-heavy oil by aqua-thermolysis. It is observed that the nano-nickel can catalyze the aqua-thermolysis reaction of extra-heavy oil at 280 °C. The experimental results demonstrate that compared with the original crude oil sample, the mean molecular weight of the upgraded sample decreases, the content of sulfur changes from 0.45% to 0.23%, the content of resin and asphaltene reduces 15.83% and 15.33%, respectively. Based on the GC-MS analysis results, a reaction pathway is proposed that involves hydrogen transfer from methylcyclohexane to the extra-heavy crude oil resulting in the formation of toluene. During the cooling process after upgrading reaction, the W/O emulsion is formed in the presence of the surfactant AEO 9. As a result, with respect to the original crude oil, the viscosity of upgraded sample is changed from 139800 mPa·s to 2400 mPa·s at 50 °C, an approximately 98.90% reduction by the synergetic effects of upgrading, emulsification and diluting.

Analysis of Products Generated from the Thermal and Catalytic Degradation of Pure and Waste Polyolefins using Py-GC/MS

The possibility of transforming waste plastics into valuable hydrocarbons via catalytic cracking and reforming is attracting increasing interest. Pyrolysis coupled with Gas Chromatographic separation and Mass Spectrometry detection (Py-GC/MS) has been used in this work to study the product selectivity of various catalysts in the conversion of pure and residual polyethylene samples into hydrocarbon products. Five acid solids of comparable aluminium contents but different textural and acid properties were tested as catalysts, including three zeolites (standard ZSM-5, nanocrystalline n-ZSM-5 and Beta) and two mesostructured solids (Al-MCM-41 and Al-SBA-15). Thermal cracking of the pure and residual polymers generated a similar range of products to each other, with a high proportion of linear paraffins and olefins of varying lengths. The presence of zeolitic materials resulted in complete elimination of heavy linear products, an increase in the light hydrocarbon fraction and a marked selectivity towards the formation of single-ring aromatic species, particularly benzene, toluene and xylene. Aromatic formation was particularly notable with the small crystal size n-ZSM-5 (aromatic selectivity up to 53.9%) and less marked in the case of standard ZSM-5 (up to 36.4%) and Beta zeolite (up to 35.0%). Mesostructured catalysts like Al-MCM-41 and Al-SBA-15 favoured the production of light C2–C5 hydrocarbons (up to 57.9%) while the formation of aromatic products was significantly lower than with zeolitic materials. The paper examines the extent and the causes for this product selectivity and discusses its connection with the acid and textural properties of each catalyst. It was also observed that, under the experimental conditions employed, the products generated were not significantly affected by the nature and origin of the polymers employed.