Studies on the conversion of isopentane over shape selective zeolites, I. H-ZSM-5 and H-ZSM-11 zeolites

H-ZSM-5 and H-ZSM-11 efficiently catalyze the conversion of isopentane into aromatic hydrocarbons.n-Pentane produces more aromatic hydrocarbons than isopentane, but at low conversion levels (high space velocity) isopentane was about two times more reactive thann-pentane in terms of the first order rate constant for the cracking of the pentane isomers.     

Selective conversion of light gasoline into aromatic hydrocarbons over shape selective zeolites, II. Effect of the reaction condition and time on stream

Zn-exchanged ZSM zeolite exhibits high activity and aromatic selectivity. The results, in concordance with Mole et al. [1], suggest that the zinc loading of ZSM zeolite changes the activation mode of light paraffins and greatly improves the effective aromatization of the intermediates.     

Selective conversion of light gasoline into aromatic hydrocarbons over shape selective zeolites, I. Catalytic activity of various zeolites for aromatization of light gasoline, heavy gasoline and coker naphtha

Studies about the development of a new effective aromatization process for converting gasoline rich in light saturated hydrocarbons, using modified molecular shapeselective zeolites, have been carried out. Naphthas with olefins and naphthenes are potential feedstocks. The yield of aromatic hydrocarbons increases with decreasing hydrogen content of the feed. Zn-SABO and Zn-ZSM type zeolites have been shown to be excellent catalysts for the process.     

m-Xylene conversion over dealuminated Y zeolites studied by the pulse method

m-Xylene conversion was studied over dealuminated Y type zeolites in hydrogen forms, SiO₂ to Al₂O₃ ratios were varied from 4.86 to 12.95.

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- . SiO₂/Al₂O₃ 4,86 12,95.

     

ZSM-5分子筛转化乙醇为乙醚的研究

用原位红外技术、程序升温热脱附和X射线光电子能谱研究了乙醇和乙醚在HZSM-5和PZSM-5上的吸附及表面状态, 并与催化乙醇为乙醚的活性和选择性相关联. 结果表明, 乙醇与质子酸中心作用形成吸附态乙醇, 该吸附态乙醇与气相乙醇反应生成吸附态乙醚, 然后从表面脱附. 磷的掺入能有效抑制积炭发生.     

催化裂化条件下噻吩与改性Y分子筛的作用机制

以HY、NiY和稀土离子改性的Y分子筛(REY)为研究对象,采用固定床装置评价噻吩模拟油催化裂化性能;运用气相色谱-氢火焰离子发光检测器(GC-FID)、气相色谱-硫化学发光检测器(GC-SCD)和原位红外光谱技术分析产物,关联分子筛的酸性,研究催化裂化条件下噻吩与改性Y分子筛的作用机制。实验结果表明,催化裂化条件下,噻吩与分子筛的作用机制差异主要取决于与B酸或L酸相关的非骨架铝物种或金属离子物种的存在形式。其中,NiY分子筛中,噻吩主要是吸附在与NiOH⁺物种相关的L酸中心,而Ni₄AlO₄³⁺等物种减弱B酸性中心从而降低其裂化性能。对HY来说,噻吩易在与AlO⁺等物种相邻的B酸中心上聚合形成三联噻吩,并发生一定的氢转移和裂化反应;而对REY而言,分子筛中与RE物种相关的L酸位会促进噻吩在与非骨架铝羟基等物种(如Al(OH)₂⁺、Al(OH)²⁺等)相邻的B酸中心形成的二联噻吩发生氢转移和裂化反应。     

n-Pentane conversion to aromatic hydrocarbons over Zn-ZSM-11 zeolite

The transformation of n-pentane into aromatic hydrocarbons over Zn-exchanged ZSM-11 zeolite (Zn-ZSM-11) has been studied. The catalyst exhibited a high activity and BTX selectivity for n-C5 conversion at about 538°C, 1 h^–1 and 1 atm. Zn-species are effective for the activation of the n-pentane and the transformation of intermediate products into aromatic compounds.

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- ZSM-11, (Zn-ZSM-11). - 538°C, 1^–1 1 . Zn - .

     

Oxidative conversion of methane on manganese-containing X zeolites

The oxidative conversion of methane has been studied on a series of manganese-containing zeolites of X type. The basic properties of the zeolite samples were investigated by means of temperature programmed desorption of CO₂. The samples 1.5% Mn/NaX manifest a good catalytic activity and selectivity, which is explained by well expressed basic properties of this sample.     

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。     

Selective ethane conversion into aromatic hydrocarbons over Zn-ZSM-11 zeolite

The conversion of ethane into aromatic compounds at 550°C and atmospheric pressure over Zn-ZSM-11 zeolite (Si/Al=17; 2.5 wt.% of Zn as counter ion) has been studied in a flow reactor at different partial pressures of ethane. The observed products at different ethane conversion levels were formed through a variety of processes including ethane dehydrogenation, producing ethylene as the only primary unstable product. Ethylene underwent very rapid reactions through carbenium ion intermediates, producing aromatic hydrocarbons and C1-C4 hydrocarbons as secondary products.     

The kinetics of hydrocarbon conversion on ZSM-5 zeolites

The complete oxidation of hydrocarbons with various structures (methane, n and wo-pentanes, cyclohexane, and benzene) on copper-modified ZSM-5 zeolite and the aromatization of propane on H-ZSM-5, are studied to analyze diffusion effects on the reaction kinetics. Comparison of the kinetic parameters of complete oxidation shows that the process rate and the rate law strongly depend on the reactant structure. Apparently, n-pentane oxidation is controlled by kinetics; the kinetics for other hydrocarbons depends on diffusion inside zeolite channels to different degrees. In the case of propane aromatization, its dehydrogenation and cracking, as well as the formation of aromatics from olefins, occurs on different active sites. Propane conversion is supposed to occur inside the zeolite channels, and the aromatization of olefins occurs on the outer surface of the zeolite crystal Deceased.     

Isomerization of dimethylnaphthalenes over zeolites

A dimethylnaphthalene (DMN) isomer mixture from a reforming unit was reacted at 350°C and atmospheric pressure over H-mordenites (Si/Al ranging from 5 to 100), a partially decationated NaY (Si/Al=2.4) and a slightly dealuminated HY (Si/Al=5), with the aim of increasing the 2,6- and 2,7-DMN content by isomerization. The best results were obtained on H-mordenite with Si/Al=10, where shape selective effects made possible to double the amount of the valuable isomers while limiting to a negligible extent the side reactions of disproportionation and dealkylation.     

Photogenerated singlet oxygen over zeolite-confined carbon dots for shape selective catalysis

Singlet oxygen as an activated oxygen species played an important role in organic synthesis. Suitable catalyst for converting ubiquitous oxygen molecule to singlet oxygen under mild conditions has attracted a wide range of attention. Herein, carbon dots have been confined into mesopores of silicalite-1 nanocrystals framework and acted as active sites for generation of singlet oxygen. The high oxygen-adsorption capacity of zeolite nanocrystals facilitated the photocatalytic generation rate of singlet oxygen, outpacing the free-standing carbon dots for 14-fold. The integrated carbon dot-zeolite nanocrystal hybrid also exhibited a special size-dependent selectivity for organic synthesis by using the in situ formed and confined singlet oxygen as active oxygen species.     

Selective conversion of methanol to p-xylene on modified high-silica zeolites

A procedure was proposed for preparation of p-xylene from a nonhydrocarbon material, methanol, in the presence of a modified ultrasil. It was shown that ultrasils modified by multiple-charge cations actively catalyze synthesis of xylenes from methanol at atmospheric pressure, and their properties can be controlled by varying the nature, charge, and size, as well as the procedure of introduction of the modifier cation. Modification of H-ultrasil with gallium led to enhanced para-selectivity (70%) of the catalysts, which was attributed to an increase in the ratio of the Lewis to Brønsted acid sites and to a decrease in the effective channel diameters of the zeolite.     

Isopropylation of naphthalene over modified-mordenite zeolites

Isopropylation of naphthalene with propylene was carried out over Ce-, Si-, La-, and Mg-modified mordenite zeolites. The reaction was performed in a 500 mL batch reactor at 300°C, 8 kg/cm², and naphthalene to catalyst weight ratio of 10:1, with excess propylene. It was attempted to eliminate the external acid sites of zeolites by these modifications. The results indicate that the CVD silanation and magnesium or cerium modification with Mg/Al or Ce/Al atomic ratios less than 0.5 can improve the 2,6-DIPN selectivity of mordenites. The improvement of catalyst performance is ascribed to the selective deactivation of acid sites on the external surface of HM zeolites.     

Transformations of aromatic hydrocarbons over zeolites

Aromatic hydrocarbons represent an important group of starting materials, intermediates, as well as final products produced in the chemical industry in the range from large processes in petrochemistry up to the synthesis of fine chemicals. This short overview covers the recent achievements in acid-catalyzed transformations of aromatic hydrocarbons with a special focus on alkylation-isomerization-disproportionation reactions in petrochemistry, and acylations or condensations used mainly in synthesis of chemical specialties. In the case of fine chemical synthesis, some zeolite applications in the preparation of important intermediates for pharmaceutical or fragrance products are presented. Advantages and disadvantages of the various types of zeolite are discussed in these reactions from the point of view of their (shape) selective properties, as well as the accessibility of acid sites.     

Dehydration of monoethanolamine over alkali-exchanged zeolites

The dehydration of monoethanolamine was carried out over a series of alkali-exchanged zeolites and aluminophosphate molecular sieves. The main product over all these samples is ethylenimine (EI). The Lewis basicity and Lewis acidity in these samples were characterized by the charges on framework oxygens and the charges on, extraframework cations divided by the square of the atomic radius, respectively, which were calculated from the Sanderson Electronegativity Equalization method (EEM). The relationship between these parameters and the EI yield suggests that the reaction is both Lewis basicity and Lewis acidity dependent. Moreover, the pore structure is also an important factor, which influences the EI formation. However, the deactivation is serious for some of these catalysts and the possible reasons for this deactivation are discussed.