Modification of Zeolite Morphology via NH4F Etching for Catalytic Bioalcohol Conversion

Various commercial zeolites, including FER, MOR, ZSM-5, BEA, and FAU frameworks, were treated with NH₄F aqueous solutions to study the effects of fluoride etching on different zeolite frameworks. NH₄F-treated small-medium pore FER, MOR, and ZSM-5 samples showed much higher mesoporosities than the untreated ones without alteration of the structural compositions and acidic properties. On the other hand, the 12-membered ring zeolites BEA and FAU showed severe dissolution of the framework aluminosilicate structure after NH₄F etching due to the high accessibility of fluoride species into the framework structures. The effect of NH₄F concentration on the fluoride treatment of H-ZSM-5 zeolite was specifically studied. From the results, we observed that structural etching with 20 wt % NH₄F was optimal for fabricating open-pore H-ZSM-5 zeolite and resulted in a high mesoporosity with comparable relative crystallinity and acidity with respect to the untreated H-ZSM-5. The catalytic activities of the open-pore H-ZSM-5 were evaluated with acid-catalyzed methanol and bioethanol conversions. Remarkably, the hierarchical open-pore H-ZSM-5 zeolite fabricated via fluoride etching exhibited an enhanced catalytic performance in bioethanol conversion with >85 % conversion over 34 h TOS and a higher catalytic stability in methanol conversion than the parent H-ZSM-5 (~50 % of bioethanol conversion at 34 h TOS).     

Ethanol conversion to aromatic hydrocarbons over several zeolite catalysts

Summary H-ZSM-5 (Si/Al₂ = 29) zeolite showed especially high activity in the conversion of ethanol to BTX (benzene, toluene, xylenes), while other zeolites exclusively formed ethylene. Noble metal catalysts supported on H-ZSM-5 (29) zeolite have high activity for the formation of BTX. Of these, Au/H-ZSM-5 catalyst can partially inhibit carbon deposition during the reaction, thus maintaining constant catalytic activity for BTX formation.     

Design of a zeolite capsule catalyst by controlling the support size for the direct synthesis of isoparaffin

Three kinds of H-ZSM-5 zeolite capsule catalysts were prepared on Co/SiO₂ catalyst pellets of different sizes. Characterization of the catalysts indicated that a defect-free H-ZSM-5 membrane had been constructed successfully on the Co/SiO₂ surface. The smaller Co/SiO₂ pellets were favorable for zeolite capsule growth under the same synthesis conditions. Zeolite capsule catalysts, especially the catalysts with smaller pellet sizes, had a higher isoparaffin selectivity compared with conventional FTS Co/SiO₂ catalyst and mixed catalyst of Co/SiO₂ with H-ZSM-5 zeolite.     

H-ZSM-11 and Zn-ZSM-11 zeolites and their applications in the catalytic transformation of LDPE

Low density polyethylene was converted into hydrocarbons over Zn- and H-ZSM-11 zeolite catalysts in a fixed-bed reactor during 20 and 60 min reaction time, 0.5 and 2.0 polymer to catalyst mass ratio at 500 °C. The zeolites were synthesized by conventional techniques and characterized by XRD, pyridine FTIR and N₂ adsorption. The adsorbed pyridine spectra demonstrated that new Lewis sites were formed after Zn exchange, and that the relationship between Lewis and Brönsted sites in the Zn-ZSM-11 zeolite (3.53) was much higher than that in the H-ZSM-11 zeolite (0.09). Thermal analyses confirmed that the temperature of decomposition of the polymer can be decreased in as much as about 145 °C when the catalysts were added. As compared to the thermal degradation, the catalytic conversion produced less solid residues and much higher amounts of gas and liquid hydrocarbons. The catalysts showed different yield profiles: the H-ZSM-11 zeolite yielded more gases, while the Zn-ZSM-11 zeolite yielded more liquid products. Notably over Zn-ZSM-11 zeolite, these liquid products were mainly aromatic, and depending on experimental conditions (higher temperature, longer reaction time, smaller polymer/catalyst relationship), aromatic selectivity could be increased to almost 100%.     

Catalytic Activity of Boron-Beta Zeolite Modified with Indium in the Epoxidation of Cinnamyl Alcohol

Liquid-phase epoxidation of cinnamyl alcohol was carried out with hydrogen peroxide as oxidizing agent using indium-containing boron- and aluminium-beta zeolites. It was proved that InO⁺ ions, created by oxidation of univalent indium cations incorporated into beta zeolite by reductive solid-state ion exchange, play an important role in the activation of hydrogen peroxide. The indium-hydroperoxo complex formed in beta zeolite pores was found to be accessible by the bulky cinnamyl alcohol molecules. Among the applied catalysts In/H[B]-beta (containing 7.6% In₂O₃/g) showed the highest selectivity in cinnamyl alcohol epoxidation.     

High pressure nitration of toluene using nitrogen dioxide on zeolite catalysts

Nitration of toluene by nitrogen dioxide in the presence of zeolite catalysts was carried out in a high pressure reaction system. Different zeolites (viz. H-ZSM-5, H-mordenite, HY etc.) were used as catalysts. The effects of NO₂/toluene molar ratio and the total pressure on the formation of mono- and di-nitrotoluenes were also investigated. The N₂-sorption capacity, X-ray diffraction analysis and catalytic activity measurements of the regenerated HY catalyst revealed that the HY catalyst can be reused.     

Template method for the synthesis of a heterogeneous fenton catalyst based on the hierarchical zeolite FeZSM-5

Zeolite h-FeZSM-5 with a hierarchical micro/macropore system has been synthesized in the presence of a template based on the close-packed polystyrene (PS) spheres, and the conventional zeolite FeZSM-5 has been obtained in the absence of a PS template. The zeolites have been characterized by X-ray diffraction, scanning and high-resolution transmission electron microscopy, and N₂ sorption. The macropore walls of the hierarchical zeolite consist of ZSM-5 nanocrystals and amorphous globules of silica. Compared to the conventional zeolite, the hierarchical one has a high BET and external surface areas of 245 and 472 m²/g, respectively, and a high pore volume of 0.6 cm³/g. The catalytic properties of the Fe-containing zeolites were studied in the H₂O₂ decomposition reaction in the absence and in the presence of EDTA ligands and in the oxidation of low- and high-molecular-weight organic compounds by hydrogen peroxide at 25°C. Hierarchical zeolite h-FeZSM-5 is highly efficient in the oxidation of large molecules.     

Nitrous Oxide Adsorption and Decomposition on Zeolites and Zeolite-like Materials

Decomposition of N₂O on modified zeolites, crystalline titanosilicalites, and related amorphous systems is studied by the catalytic and spectroscopic methods. Zinc-containing HZSM-5 zeolites and titanosilicalites with moderate Ti/Si ratios are shown to exhibit a better catalytic performance in N₂O decomposition as compared with conventionally used Cu/HZSM-5 zeolites and amorphous Cu-containing catalysts. Dehydroxylation of the HZSM-5 zeolite by calcination at 1120 K results in an enhancement of the N₂O conversion. The mechanism of the reaction and the role of coordinatively unsaturated cations and Lewis acid sites in N₂O decomposition are discussed on the basis of the spectroscopic data.     

晶种导向干凝胶法制备成型ZSM-5分子筛

在干凝胶法制备ZSM-5 分子筛的体系中添加晶种导向剂, 控制分子筛的生长, 制备了纳米沸石组装的无粘结剂成型多级孔ZSM-5 分子筛, 一步完成纳米分子筛的制备及组装成型, 即克服了传统纳米粒子难以过滤分离的问题, 同时组装所形成的多级孔有助于改善分子在催化剂内的扩散, 从而提高催化反应效率. 以硅胶、薄水铝石为原料, 四丙基氢氧化铵(TPAOH)和ZSM-5 晶种导向胶作为粘结剂, 通过混捏、挤条得到直径2 mm的条状前驱物, 随后通过干凝胶转换法制备成型分子筛. 所用晶种导向剂组成为0.35TPAOH:1SiO₂:20H₂O:4C₂H₅OH. 通过X射线衍射(XRD), 热重(TG)分析和傅里叶变换红外(FTIR)光谱等方法对分子筛晶化过程进行了表征, 结果表明晶种导向剂加入量对分子筛生长速度及多级孔结构均有影响. 当所加晶种导向剂中TPAOH与SiO₂的摩尔比为0.025时, 经过3 h晶化, 分子筛相对结晶度达到100%. 扫描电镜(SEM)结果表明, 合成的分子筛尺寸约为200 nm, 组装形成的多级孔分子筛的介孔体积为0.28 cm³·g^-1. 通过NH₃ 程序升温脱附(NH₃-TPD)考察了所得成型分子筛的酸性, 发现该分子筛酸性与市售的粉末H-ZSM-5分子筛类似.     

不同晶粒尺寸H-ZSM-5催化剂上甲醇芳构化反应性能

芳烃是一类重要的有机化工基础原料,通常采用传统的石油路线生产芳烃,包括催化裂化和催化重整等工艺.由于石油资源的紧缺,以可再生资源为原料生产芳烃工艺的发展具有十分重要的意义.甲醇作为一种重要的基础原料,可来源于煤、天然气和生物质等,因此,甲醇制芳烃工艺(MTA)的研究受到日益关注.ZSM-5分子筛具有较大的比表面积、可调节的酸性、优良的择形选择性和很高的水热稳定性,因而在甲醇芳构化中展现出良好的催化性能.研究发现,甲醇转化率和产物分布与ZSM-5分子筛的酸性和多孔性等密切相关.本文通过调控模板剂与水的比例和晶化时间,采用水热法制备了一系列不同晶粒度H-ZSM-5分子筛催化剂,通过X射线衍射(XRD)、扫描电镜(SEM)、N2物理吸附脱附(BET)和X射线荧光光谱等技术对所得分子筛的理化性质、骨架结构和形貌进行了表征;采用吡啶红外光谱和NH3程序升温脱附技术对其酸性进行了分析,使用热重(TG)技术对反应后催化剂的积碳含量进行了分析,并将所制备的H-ZSM-5分子筛催化剂分别应用于MTA反应,系统性地探究分子筛晶粒度对其理化性质和MTA催化性能的影响.XRD结果表明,所合成的五种样品均具有典型的ZSM-5分子筛特征衍射峰且无杂晶,且具有不同的晶粒度,分别为4.0±0.3,1.2±0.2 μm,614.1±31.9、391.9±32.4和99.1±7.0 nm.N2物理吸附脱附曲线可以发现,晶粒度为99.1±7.0 nm的ZSM-5分子筛展现出典型的Ⅰ型和Ⅳ型物理吸附曲线且在较高的相对压力(P/Po=0.8-1.0)处有一个明显的H4型迟滞环,表明此分子筛具有介孔和大孔结构;BJH吸附孔径分布图表明,这些介孔主要分布在2-7和20-50 nm范围内;同时各样品的比表面积和孔体积随着其晶粒度的减小而增大.结果还表明五种不同晶粒度的ZSM-5分子筛具有相似的SiO2/Al2O3摩尔比和酸性质.MTA反应结果表明,随着催化剂晶粒度的降低,甲醇的平均转化率,芳烃选择性和BTX选择性有所提高,在300 min时晶粒度较大的三个催化剂上,甲醇转化率迅速降至90％,而晶粒度较小的两个催化剂上,甲醇转化率始终维持在95％以上,其中晶粒度为99.1±7.0 nm的样品上芳烃选择性最高(平均42％以上),BTX选择性达37％.对失活催化剂积碳含量分析,随着催化剂晶粒度的降低,积碳量降低.晶粒度较低的纳米分子筛催化剂具有更短的孔道,更高效的扩散性能,更高的比表面积和独特的梯级孔结构,因而在甲醇芳构化反应中展现出更长的寿命,更高的活性和更低的积碳量,在甲醇制芳烃工业化生产中具有巨大潜力.     

Local structure of highly dispersed lead species incorporated within zeolite: experimental and theoretical studies

XAFS (both XANES and FT-EXAFS) measurements revealed that the Pb²⁺ /ZSM-5 catalyst prepared from precursor H-ZSM-5 by a conventional ion-exchange method includes a highly dispersed 3-fold coordinated Pb²⁺ ion species within the zeolite framework. UV-irradiation of Pb²⁺ /ZSM-5 led to effective decomposition of NO and N₂O producing N₂. The photocatalytic decomposition of NO is found to be slightly preferable than that of N₂O. The isolated Pb²⁺ ions play a significant role in the decomposition of pollutant NO _x . Ab initio and DFT quantum chemical studies at the HF/Lanl2dz and B3PW91/Lanl2dz levels further shed light on local structures of the Pb²⁺ active site of lead-containing zeolites, as well as on their interactions with pollutant NO and N₂O molecules. In agreement with experiments, 3-fold coordination was found to be the most favorable state for the Pb²⁺ site within the zeolite framework.     

Hydrogen yield from water radiolysis in the presence of zeolites

This paper reports a study of the decomposition of water by gamma radiolysis in the presence of zeolites ZSM-5, SAPO-5, and MOR. The irradiation is performed using ⁶⁰Co as a source with 1.12×10¹⁵ Bq activity at a 8.3 kGy/h dose rate. The stable products of radiolysis as well as the other chemical species are measured by mass spectrometry. The calculated radiation yield (G_{H 2}) generally decreases in the order: H-ZSM-5>Na-ZSM-5>H-SAPO-5>MOR under the given experimental conditions; the yield is higher in the presence of these catalysts than in their absence.     

Catalytic degradation of polyethylene using thermal gravimetric analysis and a cycled-spheres-reactor

Commercial samples of pure polyethylene were decomposed over H-ZSM-5 and Y-type zeolites using thermal gravimetric analysis (TGA) and a laboratory-scale-plant, so-called the cycled-spheres-reactor. By the TGA measurements, the activity and the deactivation behavior of the zeolite catalysts were determined. The plastic to catalyst ratio was varied to find out the optimal value for catalyst screening and for the operation of the cycled-spheres-reactor. In addition, the deactivation behavior of the zeolite catalysts was investigated. Y-type zeolites revealed lower activity and faster deactivation behavior than H-ZSM-5. Higher module of H-ZSM-5 and Y-type zeolite showed slower deactivation, but lower activity than lower module of those. Experiments in the cycled-spheres-reactor proved the results of the TGA measurements in terms of activity. The main products in the non-catalytic degradation were waxes, and when catalysts were applied, a high yield of oils was obtained at the expense of waxes. The product spectra of product oils obtained with catalysts lay mainly in the range C₄–C₁₀.     

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。     

Two routes to 1,2-cyclohexanediol catalyzed by zeolites under solvent-free condition

Two routes to 1,2-cyclohexanediol were studied. Specifically: (a) the hydrolysis of cyclohexene oxide and (b) the direct dihydroxylation of cyclohexene with aqueous hydrogen peroxide. Both reactions were carried out with zeolites as catalysts under solvent-free conditions, aiming to establish green routes for the synthesis of 1,2-cyclohexanediol. In the first route, H-Beta and H-ZSM-5 zeolites were used as catalysts, respectively. According to the results, H-ZSM-5 was a suitable catalyst for the hydrolysis of cyclohexene oxide. A 88.6 % yield of 1,2-cyclohexanediol could be obtained at a 96.2 % conversion of cyclohexene oxide under mild conditions, and the catalyst could be reused for three times. Compared with H-ZSM-5, H-Beta gave a much lower selectivity (63 %), although it was more active. In the second route, Ti-Beta zeolites with three different Ti loadings prepared via a simple two-step strategy were characterized and used. The results indicated that it was the framework Ti species which was responsible for the catalytic activity. The resultant Ti-Beta-3 % could give a 90.2 % cyclohexene conversion at a 66.2 % selectivity of 1,2-cyclohexanediol.     

亚硝胺在沸石催化剂上的程序升温表面反应

 采用程序升温表面反应技术研究了二甲基亚硝胺,吡咯烷亚硝胺和环六亚甲基亚硝胺在NaY,NaZSM－5和HZSM－5等沸石及MCM－41中孔分子筛上的脱附及分解．结果表明,沸石对亚硝胺有独特的吸附和催化分解作用．同时,研究了沸石孔结构及表面酸性对亚硝胺分解反应的影响．     

Activity of cobalt sulfide catalysts in the hydrogenolysis of dimethyl disulfide to methanethiol: Effects of the nature of a support and the procedure of supporting a cobalt precursor

The conversion of dimethyl disulfide to methanethiol on various catalysts containing supported cobalt sulfide in an atmosphere of hydrogen was studied at atmospheric pressure and T = 190°C. On CoS introduced into the channels of zeolite HSZM-5, the process occurred at a high rate but with a low selectivity for methanethiol because the proton centers of the support participated in a side reaction with the formation of dimethyl sulfide and hydrogen sulfide. Under the action of sulfide catalysts supported onto a carbon support, aluminum oxide, silicon dioxide, and an amorphous aluminosilicate, the decomposition of dimethyl disulfide to methanethiol occurred with 95–100% selectivity. The CoS/Al₂O₃ catalysts were found to be most efficient. The specific activity of alumina-cobalt sulfide catalysts only slightly depended on the phase composition and specific surface area of Al₂O₃. The conditions of the thermal treatment and sulfurization of catalysts and, particularly, the procedure of supporting a cobalt precursor onto the support were of key importance. Catalysts prepared through the stage of supporting nanodispersed cobalt hydroxide were much more active than the catalysts based on supported cobalt salts.     

C2-C2直链烯烃在HY 和H-ZSM-5分子筛上的吸附

采用ONIOM(B3LYP/6-311++G(d,p):UFF)分层计算方法, 研究了C₂-C₅直链烯烃在HY 和H-ZSM-5 分 子筛上的吸附性质. 理论计算结果表明: 烯烃与分子筛的Br?nsted 酸性位相互作用形成π配位超分子复合物; 随着碳链的增长, 烯烃的吸附能增加, 增加量近似为一个常数(HY 分子筛: 约12 kJ·mol^-1; H-ZSM-5 分子筛: 约 25 kJ·mol^-1), 与烷烃在分子筛上的吸附具有相同的规律. 双键位置对烯烃的吸附能影响很大, 2位烯烃的吸附能 要远大于1 位烯烃的吸附能. 不同类型分子筛对烯烃的吸附性能也有很大差别, 由于局域效应的影响, 小孔径 H-ZSM-5分子筛上的吸附能大于大孔径的HY分子筛,而且碳链越长,这种差别越大.从微观结构上看,吸附的烯 烃与H-ZSM-5分子筛酸性位的距离要远大于它们与HY分子筛酸性位的距离, 这是由于不同类型分子筛的微孔 结构产生的范德华作用是不同的,这种作用随着孔径的减小而增强.前线轨道分析表明, 对于小分子烯烃,大孔径 HY分子筛对其催化活性相近,而小孔径H-ZSM-5分子筛随着烯烃碳原子数的增加催化活性有减弱的趋势.     

Relationships between basicity and reactivity of zeolite catalysts

A wide variety of characterization methods, including UV-vis spectroscopy of adsorbed I₂, microcalorimetry of CO₂ adsorption, and x-ray absorption spectroscopy at the Cs L_III edge of zeolite cations, was applied to a series of alkali containing zeolites in order to elucidate the nature of the basic sites on these materials. In addition, three catalytic reactions involving basic zeolites were studied. In the first case, alkali-exchanged zeolites (L, Beta, X and Y) were used as catalysts for the side-chain alkylation of toluene with methanol to form styrene and ethylbenzene. Zeolites with low base site densities and appropriate base strengths catalyzed toluene alkylation without decomposing methanol to carbon monoxide. In the second example, ruthenium metal clusters were supported on alkali and alkaline earth exchanged X zeolites and tested as catalysts for ammonia synthesis. Zeolites containing alkaline earth ions exhibited rates greater than those containing alkali ions. Finally, zeolite X loaded with alkali metal was an active catalyst for toluene alkylation with ethylene whereas zeolite X loaded with alkali oxide was inactive for the reaction. These results suggest that exciting opportunities exist for the use of basic zeolites as catalysts and catalyst supports.     

Role of α-Sites in the selective catalytic reduction of NO x with ammonia over Fe-ZSM-5 catalysts

The catalytic properties of Fe-ZSM-5 zeolites with different iron contents have been investigated in the selective catalytic reduction (SCR) of NO _x with ammonia. The observed catalytic properties the zeolites are correlated with the concentration of the iron-containing sites that are stabilized in the zeolite and effect N₂O decomposition (??-sites). The catalysts activated at a high temperature to increase the ??-site concentration (by a factor of 5?C10) are more active in NO _x SCR with ammonia than the unactivated samples. However, the difference between the activities of the activated and unactivated catalysts is well below the difference between the ??-site concentrations in these catalysts. The nonlinear relationship between these parameters is evidence that the ??-sites in Fe-ZSM-5 is not the only factor determining the activity of Fe-ZSM-5 in NO _x SCR with ammonia. The activated catalysts show a low activity in nonselective ammonia oxidation and, accordingly, a high selectivity in the target process at high temperatures.