Catalytic cracking,dehydrogenation, and aromatization of isobutane over Ga/HZSM‐5 and Zn/HZSM‐5 at low pressures

Isobutane cracking, dehydrogenation, and aromatization over Ga/HZSM‐5 and Zn/HZSM‐5 has been investigated in a Knudsen cell reactor and the kinetics of the primary reaction steps for isobutene and propene formation have been accurately determined. Although cracking is the dominant reaction channel, with propene and methane being primary products, methane formation is significantly less than propene formation. This indicates that a proportion of the cracking proceeds via Lewis acid attack at C? C bonds, and not just via alkanium ion formation at Bronsted acid sites. This is particularly apparent over Zn/HZSM‐5. Intrinsic rate constants for cracking, calculated from the rate of propene formation, are and for dehydrogenation, calculated from the rate of isobutene formation, are Large preexponential factors for cracking and dehydrogenation over Ga/HZSM‐5 indicate that either the coverage of active sites is significantly less than the coverage of exposed sites or the intrinsic reaction step involves a large entropy change between reactant and transition state. For Zn/HZSM‐5 the small preexponential factors suggest either small entropy changes during activation, perhaps initiated by Lewis acid sites, or a steady‐state distribution of active and exposed sites is rapidly reached. Differences in intrinsic activation energies may reflect the ratio of Lewis and Bronsted acid sites on the respective catalyst surfaces. Aromatization is more prolific over Ga/HZSM‐5 than over Zn/HZSM‐5 under the low‐pressure conditions. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 467–480, 2002     

Mechanism study of the conversion of esters to high‐octane‐number aromatics over HZSM‐5

A study of the mechanism of the catalytic transformation of mixed ethyl acetate (EA) + methyl acetate (MA) (50:50 v/v) to hydrocarbons over HZSM‐5 (Si/Al ratio of 9) catalyst was conducted. The reaction was carried out in a continuous fixed‐bed reactor under atmospheric pressure and in the temperature range 250–390°C and with weight hourly space velocity of 3.2 and 4.6 h^?1. The distribution of products including monoaromatics, fused ring aromatics and oxygenates was determined using GC‐MS. The product distribution was controlled by temperature. The oxygenate components (kinetically controlled products) were transformed into aromatics (thermodynamically controlled products) with an increase in temperature. The effluents were benzene‐free or with low content of benzene and toluene. Two intermediates were proposed for this conversion to hydrocarbons over HZSM‐5: cyclobutane‐1,3‐dione and/or acetic acid (AA) as ketene source. Furthermore, AA and mesityl oxide (MO) were selected as potential intermediates in the transformation of mixed EA + MA into hydrocarbons over HZSM‐5. It is suggested that ketene dimerization, the phenolic pool and the condensation reaction between ketene and MO are the probable mechanism routes for AA conversion. Aldol condensation, Michael addition, cracking, isomerization and ketene formation are the presumable pathways for MO conversion over HZSM‐5.     

Dehydrogenation of Propane to Propylene in the Presence of CO2 over Steaming‐treated HZSM‐5 Supported ZnO

Dehydrogenation of propane to propylene over zinc oxide catalysts supported on steaming‐treated HZSM‐5 in the presence of CO₂ has been investigated. The highest catalytic performance can be achieved on the 5%ZnO/HZSM‐5(650) catalyst with the HZSM‐5 support steaming at 650°C, which allows the maximum propylene yields of 29.7% and 20.3% at the initial and steady states, respectively, in the catalytic dehydrogenation of propane at 600°C. The superior catalytic performance of this catalyst can be attributed to high dispersion of ZnO and appropriate Br?nsted acidity of the HZSM‐5(650) support. The catalytic stability is enhanced by the addition of CO₂ to the feed gas due to the suppression of coke formation.     

Effect of ketene additive and Si/Al ratio on the reaction of methanol over HZSM‐5 catalysts

The influence of ketene as possible intermediate for the reaction of methanol to aromatics was investigated over HZSM‐5 catalysts (Si/Al ratio of 15 and 9) using diketene‐acetone (2,2,6‐trimethyl‐4H‐1,3‐dioxin‐4‐one) as ketene precursor under atmospheric pressure at 300 °C. The physicochemical properties of HZSM‐5 catalysts were investigated by NH₃‐TPD, BET, XRD and ICP analysis. The distribution of products was measured by GC‐Mass spectrometer. These catalysts exhibit high reactivity and selectivity for the conversion of methanol and/or ketene to hydrocarbons (mostly high octane number xylenes, trimethylbenzenes, tetramethylbenzenes and ≤1.5% benzene). The conversion of neat diketene‐acetone over these catalysts produced aromatics compounds and significant amounts of oxygenated compounds (ketone, carboxylic acid, phenol, furan, pyran and others) depending on Si:Al ratio. These catalysts with high acid content produced small amount of saturated and unsaturated hydrocarbons without releasing significant amount of gas. The ketene and produced oxygenates from ketene appears to act as intermediates for the formation of aromatic compounds.     

Selective Transformation of Syngas into Gasoline‐Range Hydrocarbons over Mesoporous H‐ZSM‐5‐Supported Cobalt Nanoparticles

Bifunctional Fischer–Tropsch (FT) catalysts that couple uniform‐sized Co nanoparticles for CO hydrogenation and mesoporous zeolites for hydrocracking/isomerization reactions were found to be promising for the direct production of gasoline‐range (C_5–11) hydrocarbons from syngas. The Brønsted acidity results in hydrocracking/isomerization of the heavier hydrocarbons formed on Co nanoparticles, while the mesoporosity contributes to suppressing the formation of lighter (C_1–4) hydrocarbons. The selectivity for C_5–11 hydrocarbons could reach about 70 % with a ratio of isoparaffins to n‐paraffins of approximately 2.3 over this catalyst, and the former is markedly higher than the maximum value (ca. 45 %) expected from the Anderson–Schulz–Flory distribution. By using n‐hexadecane as a model compound, it was clarified that both the acidity and mesoporosity play key roles in controlling the hydrocracking reactions and thus contribute to the improved product selectivity in FT synthesis.     

纳米HZSM-5催化剂催化烃类转化反应

制备了纳米(20~50 nm)HZSM-5催化剂, 用XRF, TEM和NH3-TPD等手段对催化剂进行了表征. 以正辛烷及苯和正辛烷混合物的转化为模型反应, 研究了单烃和混合烃在纳米HZSM-5催化剂上的转化行为, 考察了反应条件对产物分布的影响. 结果表明, 纳米HZSM-5沸石催化剂具有很强的烃类转化能力, 烃类通过芳构化、 异构化和烷基化等反应转化为高辛烷值的异构烷烃和芳烃, 产物中异构烷烃(C4~C6)和芳烃的质量分数超过90%. 直链烷烃转化为芳烃以生成苯环为主, 混合烃转化为芳烃以苯和小分子烃的烷基化为主. 控制反应条件可抑制苯和C+9芳烃的生成. 产物分析结果表明, 烃类在纳米HZSM-5催化剂上的裂解、芳构化和异构化等遵循正碳离子机理.     

Catalytic Performance and Coking Behavior of a Submicron HZSM‐5 Zeolite in Ethanol Dehydration

The catalytic performance and coking behavior of a submicron ZSM‐5 zeolite in dehydration of ethanol to ethylene were investigated by means of low temperature nitrogen adsorption, thermal gravimetric analysis, and nuclear magnetic resonance. The submicron catalyst showed higher activity than the micron one due to more mesopores and more strong acid sites. As the reaction temperature increased, ethanol conversion increased over the submicron catalyst, while ethylene selectivity went through a maximum. The selectivities of propylene and butylene increased with increasing reaction temperature, and they decreased with time on stream at constant temperature. The coke deposits can be divided into coke precursor and hard coke, which were attributed to polyalkylbenzene and polycyclic aromatic hydrocarbons, respectively; and increasing reaction temperature can accelerate the transformation of coke precursor into hard coke. A precoking pretreatment method was verified very effective for improving the catalyst stability.     

超细HZSM-5沸石催化烃类芳构化反应的研究

非临氢条件下用固定床反应器研究了环己烷、辛烯-1及正辛烷在超细HZSM-5上的芳构化反应，并与微米HZSM-5作了比较。结果表明，在三种反应物中，辛烯-1反应活性最高，正辛烷次之。环己烷最低，不同反应物在两种晶粒度的HZSM-5上生成的芳烃分布大致相同，超细HZSM-5对原料的转化率、芳构化率以及自身的活性稳定性均明显高于微米沸石，在相同反应条件下超细沸石的积炭量低于微米沸石。     

Synthesis of ϵ‐Caprolactam from Cyclohexanone Oxime Using Zeolites Hβ, HZSM‐5, and Alumina Pillared Montmorillonite

The Beckmann rearrangement of cyclohexanone oxime (CHO) to ?‐caprolactam (?‐C) was studied in a plug flow reactor at 300–400°C under atmospheric pressure by using Hβ, ZSM‐5, and alumina pillared montmorillonite. With Hβ(X) Y zeolites, raising the SiO₂/Al₂O₃ molar ratio (X) results in the enhancement of catalyst acid strength with concomitant decrease of the total acid amount. In creasing the calcination temperature (Y) causes remarkable diminution of catalyst surface area, acid strength, and acid amount. A similar trend was found for AlPMY catalysts. In there action of CHO, the initial catalytic activity correlates well with the total acid amount of various catalysts except for Hβ(10) Y (Y > 600°C). The reaction proceeds on both Brönsted and Lewis acid sites and the catalyst deactivation most likely occurs at the strong Brönsted acid sites. The effect of solvents in the feed on the catalytic results was also investigated; it was found that polar solvents such as ethanol or n‐butanol give high ?‐C yield and longer catalyst life time. In the reaction of CHO/C₂H₅OH over Hβ(10)800 at 400°C and W/F 74.6 gh/mol, the CHO conversion and ?‐C yield remain 100% and 92%, respectively, for at least 20 h time‐on‐stream. The reaction paths and the mechanism for ?‐C formation are proposed.     

Propane‐1,2‐diols from Dilactides,Oligolactides, or Poly‐L‐lactic Acid (PLLA): From Plastic Waste to Chiral Bulk Chemicals

The preparation of racemic or enantioenriched propane‐1,2‐diol from dilactides, oligolactides, or poly‐L ‐lactic acid (PLLA) is described. The transformation is carried out as tandem reactions in MeOH, covering hydrolysis and subsequent hydrogenation by using copper chromite as a catalyst. The starting material present undesired side products of the PLLA synthesis or PLLA waste.     

Reinvestigation of the Synthesis of Ketanserin (5) and its Hydrochloride Salt (5.HCl) via 3‐(2‐Chloroethyl)‐2,4‐(1H,3H)‐quinazolinedione (2) or Dihydro‐5H‐oxazole(2,3‐b)quinazolin‐5‐one (1)

The synthesis of ketanserin ( 5 ) and its hydrochloride salt ( 5.HCl ) using respectively equimolar amounts of 3‐(2‐chloroethyl)‐2,4‐(1H,3H)‐quinazolinedione ( 2 ) with 4‐(parafluorobenzoyl)piperidine ( 3 ) and dihydro‐5H‐oxazole(2,3‐b)quinazolin‐5‐one ( 1 ) with hydrochloride salt of 4‐(parafluorobenzoyl)piperidine ( 3.HCl ) is reinvestigated. The one‐pot reaction of ethyl‐2‐aminobenzoate with ethyl chloroformate and ethanol amine has afforded 3‐(2‐chloroethyl)‐2,4‐(1H,3H)‐quinazolinedione ( 2 ) (86%) that was then refluxed with 4‐(parafluorobenzoyl)piperidine ( 3 ) in ethyl methyl ketone in the presence of sodium carbonate to obtain free base of ketanserin (87%). In another attempt, a very pure hydrochloride salt of ketanserin ( 5.HCl ) was synthesized using equimolar amounts of dihydro‐5H‐oxazole(2,3‐b)quinazolin‐5‐one ( 1 ) and hydrochloride salt of 4‐(parafluorobenzoyl)piperidine ( 3.HCl ) by a solvent‐less fusion method. Thus, under optimized conditions, 180°C and a reaction time of 30 min, the powder mixture was transformed into glassy crystals that were initially readily soluble in chloroform but were transformed afterwards over time (2 h) to white precipitates ( 5.HCl ) suspended in chloroform with a yield of 72%.     

Predicting adsorption enthalpies on silicalite and HZSM‐5: A benchmark study on DFT strategies addressing dispersion interactions

We evaluated the accuracy of periodic density functional calculations for adsorption enthalpies of water, alkanes, and alcohols in silicalite and HZSM‐5 zeolites using a gradient‐corrected density functional with empirical dispersion corrections (PBE‐D) as well as a nonlocal correlation functional (vdW‐DF2). Results of both approaches agree in acceptable fashion with experimental adsorption energies of alcohols in silicalite, but the adsorption energies for n‐alkanes in both zeolite models are overestimated, by 21?46 kJ mol^?1. For PBE‐D calculations, the adsorption of alkanes is exclusively determined by the empirical dispersion term, while the generalized gradient approximation‐DFT part is purely repulsive, preventing the molecule to come too close to the zeolite walls. The vdW‐DF2 results are comparable to those of PBE‐D calculations, but the latter values are slightly closer to the experiment in most cases. Thus, both computational approaches are unable to reproduce available experimental adsorption energies of alkanes in silicalite and HZSM‐5 zeolite with chemical accuracy. © 2014 Wiley Periodicals, Inc.     

(S)‐3‐(Ammoniomethyl)‐5‐methylhexanoate (pregabalin)

The title compound, C₈H₁₇NO₂, exists as a zwitterion, adopting a propeller conformation. Molecules self‐assemble to form a hydrogen‐bonded layer parallel to the ab crystallographic plane connected by N⁺—H...O⁻ and C—H...O⁻ hydrogen bonds. These layers are stacked along the c axis and are stabilized by van der Waals interactions.     

Syntheses and Anti—inflammatory Actiobn of （η—C5H5）2Ti （Cin）2 and （η—C5H5）2Ti（Tzea）2

Two new Complexes(Cp)2Ti(Cin)2and (CP2)Ti(Tzea)2(CP=Cyclopentadienyl η^5-C5H5)have been synthesized in THF by the reaction of HCin(Cincofen,2-phenylquinoline-4-carboxylic acid)or HTzea(5-phenyltetrazolyl-2-ethanoic acid)with(Cp)2TiCl2,and characterized by elemental analyses,IR,1H NMR and 13C NMR,UV spectra,molar conductivity,TGDTA.In the complexes the carboxyl groups are coordinated to Ti(IV)in a monodentate manner,The inhibitory actions of the complexes on mice ear tumefaction caused by croton oil and the rat foot granulation growth produced by cotton wool are higher than those of the corresponding ligands HCin,HTzea and [(Cp)2TiCl2],while their toxicities are lower than those of the free ligands.ηη     

Synthesis of 3‐phenyl‐5‐(trifluoromethyl)isoxazole and 5‐phenyl‐3‐(trifluoromethyl)isoxazole

Reaction of 4,4,4‐trifluoro‐1‐phenyl‐1,3‐butanedione with hydroxylamine led to the formation of 5‐hydroxy‐3‐phenyl‐5‐(trifluoromethyl)‐4,5‐dihydroisoxazole which was dehydrated to 3‐phenyl‐5‐(trifluoro‐methyl)isoxazole. This isomer can also be synthesized by reaction of 4‐chloro‐4‐phenyl‐1,1,1‐trifluoro‐3‐buten‐2‐one with sodium azide. The regioisomer, 5‐phenyl‐3‐(trifluoromethyl)isoxazole was synthesized by reaction of 1,1,1‐trifluoro‐4‐phenylbut‐3‐yn‐2‐one with hydroxylamine and by the reaction of 3‐chloro‐1‐phenyl‐4,4,4‐trifluorobut‐2‐en‐1‐one with sodium azide. Both isomers were characterized by mass and NMR spectroscopy.