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.     

Effect of weak base modification on ZSM‐5 catalyst for methanol to aromatics

The effect of weak base modification on the catalytic performance of ZSM‐5 catalyst for conversion of methanol to aromatics was investigated. The catalysts were characterized using X‐ray diffraction, X‐ray fluorescence, N₂ adsorption–desorption, NH₃ temperature‐programmed desorption, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetry. The results showed that catalysts treated with weak base (NaHCO₃, Na₂CO₃ and NH₃⋅H₂O) exhibited a pore structure with interconnected micropores and mesopores. The existence of mesopores was beneficial for improving the diffusion of reactants and products, and the coke deposition resistance capacity of treated catalysts was enhanced greatly. Meanwhile, compared to traditional ZSM‐5 zeolite, the ratio of Brønsted to Lewis (B/L) acid sites of ZSM‐5/NH₃⋅H₂O (B/L = 7.35) zeolite slightly increased but the amount of acid sites reduced, while those of ZSM‐5/NaHCO₃ (B/L = 0.127) and ZSM‐5/Na₂CO₃ (B/L = 0.107) significantly reduced. Further, the catalyst treated with NH₃⋅H₂O solution was evaluated in the methanol to aromatics reaction and led to an enhanced aromatization reaction rate. The liquid hydrocarbons product distribution exhibited higher aromatic hydrocarbons yield (56.12%) and selectivity (40.28%) of benzene, toluene and xylene (BTX) with isoparaffin content reducing to 26.17%, which could be explained by appropriate B/L acid sites ratio, higher pore volumes and higher surface area.     

An embedded QM/MM study for different SiO2/Al2O3 ratios of the HZSM‐5 zeolite and for their interaction with n‐heptane

We carried out a theoretical study of the HZSM‐5 zeolite, for different SiO₂/Al₂O₃ ratios, that interacts with the n‐heptane molecule. The study was performed using a QM/MM (quantum mechanics/molecular mechanics) methodology. For the QM part, we have chosen a hybrid Hartree‐Fock density functional theory (DFT). The hybrid ACM/DZP approach, as implemented in Turbomole, was used for the treatment of the QM cluster containing 84 atoms that represents a ring structure model of the zeolite‐n‐heptane interacting system. The MM part was represented by means of an electrostatic forcefield (ESFF), which assesses the electronic embedding. The chosen QM/MM silicalite base model contains 3862 atoms. The studied SiO₂/Al₂O₃ ratios were 2300, 573.5, 287.7, and 189.83, containing 1, 4, 8, and 12 Al atoms, respectively. For the first ratio, the site for the substitution of Al for Si was that of minimum QM total energy value, because this replacement was done in the QM region. For the other SiO₂/Al₂O₃ ratios, the Al atoms were randomly spread through the MM region in accordance with the Lowenstein substitution rule. These results show the importance of the environment on the electronic properties in the QM region, where the active site lies, and their effects on the earlier steps on the activation experienced by the n‐heptane moiety. A minimal content of 12 Al atoms produces significant effects of the environment on the electronic structure of the QM region. Moreover, the carbocationic character of n‐heptane increases with the aluminum content. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

ZSM-5分子筛骨架铝落位对甲醇转化制芳烃催化性能影响

采用水热合成法,在合成过程中通过添加矿化剂、尿素和改变硅源,制备了不同骨架铝落位的ZSM-5分子筛。通过SEM、XRD、BET、XRF、MAS NMR、NH_3-TPD和Py-FTIR等表征手段对分子筛的形貌、织构、骨架铝落位和酸性进行了系统研究,同时考察了不同ZSM-5分子筛催化剂甲醇制芳烃的催化性能。研究结果表明,制备的ZSM-5分子筛均具有结晶度高和形貌均一等特点,但在骨架铝落位和酸性方面存在显著差异。椭球状ZSM-5分子筛的骨架铝主要分布于直通孔道或正弦孔道中,并表现出较多的酸性位。块状分子筛中骨架铝主要落位在孔道交叉处,且具有较低的强酸量。在甲醇制芳烃反应中,骨架铝主要位于直通或正弦孔道并表现出较多酸性位的椭球状ZSM-5分子筛催化剂具有较高的活性稳定性和芳烃选择性。     

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.     

Coupling of Methanol and Carbon Monoxide over H‐ZSM‐5 to Form Aromatics

The conversion of methanol into aromatics over unmodified H‐ZSM‐5 zeolite is generally not high because the hydrogen transfer reaction results in alkane formation. Now circa 80 % aromatics selectivity for the coupling reaction of methanol and carbon monoxide over H‐ZSM‐5 is reported. Carbonyl compounds and methyl‐2‐cyclopenten‐1‐ones (MCPOs), which were detected in the products and catalysts, respectively, are considered as intermediates. The latter species can be synthesized from the former species and olefins. ¹³C isotope tracing and ¹³C liquid‐state NMR results confirmed that the carbon atoms of CO molecules were incorporated into MCPOs and aromatic rings. A new aromatization mechanism that involves the formation of the above intermediates and co‐occurs with a dramatically decreased hydrogen transfer reaction is proposed. A portion of the carbons in CO molecules are incorporated into aromatic, which is of great significance for industrial applications.     

氧化锆催化合成气直接转化制芳烃

采用共沉淀法和水热法制备了三种不同粒径、不同结构的纳米氧化锆催化剂,借助XRD、TEM、Raman光谱、N_2物理吸附、XPS、NH_3-TPD表征了催化剂的物理化学性质,并研究了其合成气催化转化性能。在400℃、3 M Pa、空速500 m L/(gcat·h)、进料组成H_2/CO/Ar(体积比)为5∶5∶1时,氧化锆能够一步催化合成气转化为高辛烷值烃类产物,主要是异构烯烃、环状烯烃及芳烃。在烃类产物中,C_(5+)选择性高达48%,C_(5+)中芳烃含量为30%-53%。结果表明,单斜相氧化锆比四方相更有利于CO转化,其中,比表面积较大、酸量较大的小粒径氧化锆表现出最高的CO转化率及产物收率;而大晶粒单斜相氧化锆表现出最高的芳烃选择性,这与其较高的酸性位密度相对应。因此,CO转化在Zr O_2催化剂上是酸催化反应,酸量影响催化剂的活性,而酸性位密度是影响芳烃等较大分子量产物生成的主要因素。     

生物质衍生物γ-戊内酯催化转化制芳烃和2-环戊烯酮的研究

应用浸渍法在ZSM-5沸石分子筛孔道中引入过渡金属Zn物种,制备了具有不同Zn含量的Zn/ZSM-5。考察了反应温度、催化剂用量、催化剂的酸性性质等条件对γ-戊内酯芳构化产物组成(气、液、固产物)及其液体成分含量的影响。实验结果表明,ZSM-5分子筛孔道中引入Zn后,可以有效改变液体产物成分以及影响气体和固体产物收率。当ZSM-5分子筛孔道中引入Zn物种后,能够明显提高液体产物中苯、甲苯、乙苯、萘等芳香类化合物的含量,表明Zn物种能促进γ-戊内酯芳构化反应的进行。     

H-ZSM-5分子筛形貌对ZnCr2O4/H-ZSM-5双功能催化剂合成气制芳烃催化性能的影响

采用水热法，通过改变合成条件选择性制备出具有球状堆积、薄片状、中空和海绵条状结构的四种不同形貌的H-ZSM-5分子筛，并采用XRD、SEM、Py-FTIR、NH₃-TPD、ICP和N₂物理吸附等手段对其结构性质进行了表征。将具有尖晶石结构的ZnCr₂O₄复合氧化物与不同形貌的H-ZSM-5分子筛组成ZnCr₂O₄/H-ZSM-5双功能催化剂，应用于合成气直接制芳烃（STA）的反应过程，研究了H-ZSM-5分子筛形貌对该双功能催化剂STA性能的影响。结果表明，H-ZSM-5分子筛形貌对ZnCr₂O₄/H-ZSM-5的合成气制芳烃催化性能具有重要影响；不同形貌H-ZSM-5分子筛的芳烃选择性由高到低顺序依次为球状堆积 > 海绵条状 > 中空结构 > 薄片状结构。其中，ZnCr₂O₄氧化物与具有球状堆积结构的H-ZSM-5分子筛组成的ZnCr₂O₄/H-ZSM-5（sphere）双功能催化剂在STA反应过程中表现出最佳的催化性能：在350℃和3.0 MPa条件下，CO转化率为12.6%，芳烃选择性高达68.8%，而甲烷、C_2-4⁰烷烃和CO₂选择性分别降低至1.3%、14.3%和41.4%。这是由于球状堆积H-ZSM-5分子筛粒径适中（约350 nm），孔道长度适宜，适合芳烃产物的扩散但又能避免低碳烃类过早扩散出酸性分子筛孔道，从而有利于合成气转化中间产物的芳构化，提高芳烃产物的选择性。     

Effect of acid strength distribution on conversion of FCC gasoline over a ZSM-5 zeolite catalyst

Summary Acid strength distribution and the distribution of aromatics formed in the FCC gasoline conversion reaction on a ZSM-5 zeolite with different Na contents have been studied. With increasing Na content in the ZSM-5 zeolite, the acid sites determined by NH₃-TPD technique, especially the strong acid sites, clearly decrease. When used as catalyst for the aromatization reaction, the transformation of olefins in the FCC gasoline into aromatics is governed directly by the strong acid sites on the ZSM-5 catalyst. Only under the conditions that a ZSM-5 catalyst possesses suitable strong acid sites is reaction temperature favorable for the aromatics formed.     

Determination of phthalate esters from environmental water samples by micro‐solid‐phase extraction using TiO2 nanotube arrays before high‐performance liquid chromatography

We describe a highly sensitive micro‐solid‐phase extraction method for the pre‐concentration of six phthalate esters utilizing a TiO₂ nanotube array coupled to high‐performance liquid chromatography with a variable‐wavelength ultraviolet visible detector. The selected phthalate esters included dimethyl phthalate, diethyl phthalate, dibutyl phthalate, butyl benzyl phthalate, bis(2‐ethylhexyl)phthalate and dioctyl phthalate. The factors that would affect the enrichment, such as desorption solvent, sample pH, salting‐out effect, extraction time and desorption time, were optimized. Under the optimum conditions, the linear range of the proposed method was 0.3–200 μg/L. The limits of detection were 0.04–0.2 μg/L (S/N = 3). The proposed method was successfully applied to the determination of six phthalate esters in water samples and satisfied spiked recoveries were achieved. These results indicated that the proposed method was appropriate for the determination of trace phthalate esters in environmental water samples.     

Centrifugeless ultrasound‐assisted emulsification microextraction based on salting‐out phenomenon followed by high‐performance liquid chromatography for the simple determination of phthalate esters in aqueous samples

A fast, sensitive, and centrifugeless ultrasound‐assisted emulsification microextraction followed by a high‐performance liquid chromatography method is developed for the determination of some phthalate esters in aqueous samples. In this method, a simple approach is followed to eliminate the centrifugation step in dispersive liquid–liquid microextraction using an organic solvent whose melting point is near the ambient temperature, consumption of the extracting solvent is efficiently reduced, and the overall extraction time was found to be only 7 min. The variables affecting the method are optimized. Under the optimal experimental conditions (75 μL of 1‐undecanol, a flow rate of 2.0 mL/min, and an ultrasound irradiation of 1 min), the proposed method exhibits good preconcentration factors (52–97), low limits of detection (1.0–5.0 ng/mL), and linearities in the range of 5–1500 ng/mL (r ² ≥ 0.995). Finally, the method is successfully applied to the analysis of phthalate esters in the drinking and river water samples. To study the probable release of the phthalate esters from a polyethylene container into boiling water, the boiling water exposed to the polyethylene container was analyzed by the proposed method.     

New application of chitosan‐grafted polyaniline in dispersive solid‐phase extraction for the separation and determination of phthalate esters in milk using high‐performance liquid chromatography

Chitosan‐grafted polyaniline was synthesized and applied as a sorbent for the preconcentration of phthalate esters in dispersive solid‐phase extraction. By coupling dispersive solid‐phase extraction with high‐performance liquid chromatography and response surface methodology (central composite design), a reliable, sensitive, and cost‐effective method for simultaneous determination of phthalate esters including dimethyl phthalate, di‐n‐butyl phthalate, and di(2‐ethylhexyl)phthalate was developed. The morphology of sorbent had been studied by scanning electron microscopy and its chemical structure confirmed by Fourier transform infrared spectroscopy. Under optimum condition, good linearity was observed in the range of 5.0–5000.0 ng/mL. The limits of detection (S/N = 3) and limits of quantification (S/N = 10) were 0.1–0.3 and 0.3–1 ng/mL, respectively. The relative standard deviations were less than 8.8%. Finally, this procedure was employed for extraction of trace amounts of phthalic acid esters in milk samples, the relative recoveries ranged from 82 to 103%.     

Formaldehyde intermediate participating in the conversion of methanol to aromatics over zinc modified H-ZSM-5

Metal-modified H-ZSM-5 has a high selectivity of aromatics in methanol to aromatics(MTA)reaction,which is often attributed to the metal promoting the aromatization of intermediate olefins.However,the effect of methanol dehydrogenation on aromatics formation over these catalysts is rarely studied.Here,we report that HCHO,which is formed by methanol dehydrogenation over Zn/H-ZSM-5 prepared by Zn impregnation,can participate in the synthesis of aromatics.Methanol conversion can produce more aromatics than olefins(propylene or ethylene)conversion over Zn/H-ZSM-5,indicating the conventional MTA pathway including methanol-to-olefins and olefins-to-aromatics is not complete.Moreover,an MTA mechanism including the conventional pathway and the methanol and HCHO coupling pathway is systematically proposed.     

Supported dual‐acidic 1,3‐disulfoimidazolium chlorozincate@HZSM‐5 as a promising heterogeneous catalyst for synthesis of indole derivatives

HZSM‐5‐supported Brönsted and Lewis acidic ionic solid 1,3‐disulfoimidazolium chlorozincate materials ([dsim]₂[ZnCl₄]@HZSM‐5) were synthesized with various ratios (3, 6, 9, 17 and 50% w/w). The heterogeneous materials were characterized via a variety of spectroscopic techniques. Dual acidity of these materials was determined using specified techniques. These acidic solids were examined as stable heterogeneous catalysts for the Fischer indole reaction of equimolar amounts of phenylhydrazine hydrochloride and various aliphatic or aromatic ketones at 80–90°C in neat condition to produce substituted indole derivatives. The efficient 17% ionic salt‐loaded HZSM‐5 composite was easily reused for ten consecutive cycles with a slight loss of its activity. The recycled catalyst was further analysed using powder X‐ray diffraction and inductively coupled plasma optical emission spectrometric techniques.     

H-ZSM-5分子筛硅铝比对其催化的甲醇转化丙烯选择性的影响

本研究合成了一系列硅铝比不同（SiO₂/Al₂O₃=50-4000）,但晶粒粒径相近的ZSM-5分子筛,并考察了硅铝比对甲醇转化反应丙烯选择性的影响。采用XRD、N₂吸附-脱附、NH₃-TPD和Py-FTIR方法对合成的HZSM-5分子筛进行物化性质表征。实验结果表明,随着硅铝比的增大,初始甲醇转化率降低,其中,硅铝比为50-1600的样品可以实现甲醇的完全转化。在甲醇完全转化的条件下,随着硅铝比的增大,丙烯选择性单调增加,从机理角度出发,揭示了甲醇转化制丙烯反应中,甲基化/裂化循环相较于甲基化/脱烷基化循环进行程度更大。此外,本研究提出了在甲醇完全转化条件下,保证最大丙烯选择性所需要的临界酸密度值（[AS]_S）,当甲醇进料量为0.162g/min时,该临界值为0.175μmol/m²。     

Co改性Mo/HZSM-5催化剂上甲烷无氧芳构化反应研究

甲烷无氧芳构化催化剂Ｍｏ／ＨＺＳＭ－５上担载第二组分Ｃｏ后,提高了催化剂的稳定性,但加快了催化剂上的积炭速率,且积炭速率随Ｃｏ添加量的增加而提高,因而认为催化剂的失活速率与积炭速率并不成顺比关系,研究认为,一方面,Ｃｏ的添加增加了催化剂的脱氢能力,使更多的中间产物乙烯进一步脱氢转化成芳烃或积炭,另一方面,增加了催化剂的抗积炭能力。并认为部分积炭可能对提高催化剂的稳定性起到一定的作用,空速实验表明,     

Fragmentation Mechanism of Trans—α—Aryl—β—enamino Esters

Electron impact-induced fragmentation mechanism of Trans-α-Aryl-β-enamino esters were investigated using mass-analyzed ion kinetic energy (MIKE) spectrometry and high resolution accurate mass data It was found that the main characteristic fragmentations of compounds studied were:an odd electron ion M^ -EtOH was formed by losing a neutral molecule of ethanol;and the skeletal rearrangements took place;and the ring opening reaction happened after losing a carbon monoxide;and the typical McLafferty rearrangement underwent in ester group.The cycliztion reation caused by losing neutral molecule of TsNH2 due to the ortho-effects of substituted group of gromatic ring was also observed.