Recent Advances in Reactions of Alkylbenzenes Over Novel Zeolites: The Effects of Zeolite Structure and Morphology

Alkylbenzenes form an important segment of petrochemical industry for the manufacture of widely used commodities and specialty products. Since the last review on this topic (8), numerous new zeolite-based catalysts have been synthesized, characterized and evaluated in various transformations of aromatic hydrocarbons. This comprehensive review covers major reactions of mono-, di-, and tri-alkylbenzenes such as disproportionation, alkylation, transalkylation, isomerization, etc., over different zeolite-based acid catalysts. During the last decade, significant progress was made in the synthesis and structure determination of novel zeolites, mesoporous single crystals, hierarchic zeolites and two-dimensional zeolites. These developments have enhanced the understanding of the role of zeolites (effects of structural type, morphology, acid sites, accessibility of acid sites, shape selectivity factors) in transformations of aromatics. In this review, the emphasis is on the influence of the type of acid sites, zeolite topology, and reaction conditions on the activity, selectivity and pathways of these reactions. Thermodynamics and reaction kinetics of transformations of aromatic hydrocarbons are also discussed. This article covers mostly literature published during the period of 2002–2013.     

Y型分子筛应用于双环芳烃加氢裂化多产轻芳烃过程研究进展

催化柴油富含双环芳烃，可通过加氢裂化过程选择性多产高价值轻质芳烃（BTX）产物，现有研究已对此过程所需的工艺条件和催化剂性质进行了大量考察。工业应用中催化剂的酸性组分以Y型分子筛为主，研究分子筛性质和反应结果的关系成为重点内容。本文主要介绍了双环芳烃多产BTX产物经历加氢饱和、开环、断侧链等主要反应过程，金属组分及其与分子筛的协同作用；总结了Y型分子筛的性质如孔道性质、小晶粒、酸性质、核壳结构等因素对上述反应过程的影响。初步表明分子筛孔性质、酸性质直接影响目标反应选择性，通过对分子筛性质进行调变，可以达到促进反应物有效转化及提高BTX产物收率的目的。     

Transalkylation and disproportionation of toluene and C9 aromatics over zeolite beta

Transalkylation and disproportionation (TADP) of toluene and C₉ aromatics from a commercial stream have been studied over a zeolite possessing a three-dimensional, 12-membered ring pore system. The study encompassed the effect of C₉ aromatics content in feed on TADP. Formation of xylenes was maximum with a feed containing 50 50 toluene and C₉ aromatics. In order to understand the role of different C₉ aromatics in TADP, experiments using individual C₉ aromatics with and without toluene mixture as feed were carried out. An interesting observation of these experiments was that ethyltoluenes produced xylenes through disproportionation of toluene generated from their deethylation. The total yield of xylenes was much less than that obtained from trimethyl benzenes. A reaction scheme accounting all the reactions taking place during TADP is proposed.     

多级孔分子筛在重油加氢裂化催化剂的应用进展

分子筛是加氢裂化催化剂关键组分,其性质影响着加氢裂化反应效率和产品分布。微孔分子筛的孔结构降低了大分子反应物的扩散效率和酸中心的可及性,不宜直接用作加氢裂化催化剂的载体。本文从分子筛的孔结构和酸中心可及性的角度出发,介绍了具有多级孔体系的分子筛和具有核壳结构分子筛的加氢裂化性能。与相应的参比剂比较,分子筛的多级孔结构能大幅提高反应物种的扩散效率和酸中心的可及性,呈现出更好的催化活性、稳定性以及目标产物选择性。此外,金属加氢活性中心与分子筛裂化活性中心的合理调配,也是多级孔分子筛在重油加氢裂化应用中面临的挑战。     

Selective toluene disproportionation over ZSM-5 zeolites

Selective toluene disproportionation to benzene and xylenes is investigated over HZSM-5 and modified HZSM-5 zeolites. The zeolites are modified with nickel, magnesium, phosphorus and boron, characterised by sorption, acidity measurement and X-ray photoelectron spectroscopy, and their activity towards toluene disproportionation is discussed in the light of their physico-chemical properties. The two types of active sites have been identified; one promoting disproportionation and the other cracking and dealkylation of toluene. It is found that the latter sites are suppressed due to incorporation of the modifiers. The modified zeolites are found to be para-selective which appears to be consistent with the commonly accepted view that modifiers like magnesium, phosphorus and boron reside in the channels and react with Brønsted acid sites, leading to partial blockages and thus favouring the formation of p-xylene. The effect of poisoning the zeolite with 1-methylisoquinoline is also investigated. In the case of poisoned catalyst, p-xylene is produced at levels up to 99%. The total elimination of other isomers from the products is suggested due to the selective poisoning of the non-selective sites (on the external crystal surface) and to partial blocking of the pore openings.     

On the exceptional time-on-stream stability of HZSM-12 zeolite: relation between zeolite pore structure and activity

ZSM-12 and several other 12-membered ring large-pore zeolites have been tested for the reforming of naphthenic hydrocarbon mixtures. It was found that ZSM-12 possesses a surprisingly higher coking resistance than other large pore zeolites tested such as USY, L-zeolite, mordenite, and β=zeolite for reforming of hydrocarbon mixtures. This superior performance is due to the unique non-interconnecting tubular-like linear channels of ZSM-12, which do not allow trapping/accumulation of coking precursors. ZSM-12 zeolite also demonstrated excellent structural stability even under severe acid dealumination. From this work, we found that the decrease of the aluminum content of a zeolite is not sufficient to ensure low rates of coke deposition. We also concluded that zeolites with channel intersections (cavities) of comparable size with the zeolite apertures do not favor coke formation. For these types of zeolites the strong acid sites carry out other acid-catalyzed reactions, rather than forming coke. In contrast, zeolites with relatively large supercages are inherently favorable to coking reactions, which in turn lead to the fast deactivation. The appropriate combination of the zeolite pore structure and acidity (controlled via dealumination) showed superior TOS behavior (time-stable activity and product selectivities). For zeolites which are susceptible to coking due to pore structure, the increase of the Brønsted acid strength results in fast deactivation. Contrary to what one would commonly expect and previous reports, we found that one-dimensional zeolites, such as, ZSM-12, can exhibit significantly higher tolerance to coking than multidirectional zeolites.     

Organosilane surfactant-assisted synthesis of mesoporous SSZ-39 zeolite with enhanced catalytic performance in the methanol-to-olefins reaction

SSZ-39 zeolite with AEI framework structure is a good catalyst candidate for the methanol-to-olefins (MTO) reaction. However, the diffusion limitation and coke formation often results in fast deactivation of the SSZ-39 zeolite catalyst. One solution for this challenge is to introduce mesoporosity in the SSZ-39 zeolite. Herein, we report the synthesis of mesoporous SSZ-39 zeolite using an organosilane surfactant, N,N-dimethyl-N-(3-(trimethoxysilyl)propyl)octan-1-aminium chloride, as a mesopore template and N,N-dimethyl-cis-2,6-dimethylpiperidinium as a micropore template. The obtained zeolites were characterized by X-ray diffraction, N₂ sorption, scanning electron microscopy, temperature programmed desorption of ammonia, and magic angle spinning nuclear magnetic resonance of ²⁷Al. The results show that the mesoporous SSZ-39 zeolite has high crystallinity, meso/microporosity, high surface area, cuboid morphology, and abundant acidic sites. More importantly, this mesoporous SSZ-39 zeolite exhibits enhanced catalyst lifetime in the MTO reaction due to the presence of mesoporosity for fast mass transfer, compared with a conventional SSZ-39 zeolite without mesoporosity.     

Zeolite Beta with hierarchical porosity prepared from organofunctionalized seeds

Beta zeolite with hierarchical porosity has been obtained by a new synthesis strategy, based on perturbing the growth of the zeolite crystals by functionalization of the zeolitic seeds with organosilanes in order to hinder and prevent their further aggregation and agglomeration. As a consequence, a secondary porosity in the supermicropore region has been generated in zeolite Beta, leading to a considerable increase in both the total surface area and the pore volume of the material. The enhancement of the textural properties can be controlled by changing the silanization agent molecular size and its quantity added to the synthesis medium. This type of hierarchical Beta zeolites presents interesting applications as catalysts in reactions involving bulky molecules. Thus, their catalytic activity in the catalytic cracking of LDPE has been found to be strongly enhanced compared to a standard Beta zeolite sample, due to the higher accessibility to the acid sites caused by the presence of the secondary porosity.     

SSZ-13沸石粒径及硅铝比对甲醇制烯烃反应性能的影响

通过调控合成配方,以水热合成法制备一系列不同粒径及硅铝比的SSZ-13沸石,考察沸石孔道结构、酸性质与催化性能之间的关系。采用XRD、SEM、XRF、N₂吸附-脱附以及²⁷Al MAS NMR对沸石样品进行详细的表征,并评价其甲醇制烯烃反应(MTO)催化性能。结果表明,小晶粒SSZ-13沸石相对结晶度高、晶粒尺寸均一;在MTO中,小晶粒SSZ-13沸石的MTO催化寿命大幅高于大晶粒SSZ-13沸石;减小晶粒尺寸可改善分子扩散效率,在此基础上提高沸石的酸密度可增加其活性稳定性。     

几种沸石分子筛的催化裂化性能研究:1孔结构和酸性

采用X-射线衍射、X射线荧光光谱、N2吸附、吡啶吸附红外光谱和NH3程序升温热脱附研究了分子筛RE-HY,HZSM-5和Hβ的基本物理化学性质。N2吸附结果表明,三维孔道结构的REHY分子筛和Hβ分子筛具有相近的孔半径和吸附量;与HZSM-5和Hβ分子筛相比,高温条件下,REHY分子筛具有较多的Brφsted酸中心和较少Lewis酸中心。NH3程序升温热脱附表明,三种分子筛中,HZSM-5分子筛的强酸中心最多。     

酸碱复合改性丝光沸石催化4-异丙基联苯异丙基化

采用酸碱复合改性的方法,制备了同时具有微孔和介孔孔道的丝光沸石,用于固定床4-异丙基联苯的异丙基化反应。通过X射线衍射(XRD)、透射电子显微镜(TEM)、NH3程序升温脱附(NH3-TPD)、N2物理吸附脱附等方法对改性丝光沸石进行表征。结果表明,碱改性处理调变了丝光沸石的孔道结构和酸性质,同时保持了其MOR拓扑结构,提高了4-异丙基联苯的转化率和反应的稳定性。碱处理后再进行酸处理,可以有效清除碱处理过程中产生的非骨架铝物种和样品外表面的酸中心,提高目的产物4,4'-二异丙基联苯的选择性。     

De-t-butylation of t-butylphenols over dealuminated zeolites in liquid-solid system

Liquid-solid phase de-t-butylation of p-t-butylphenols was carried out over original and dealuminated zeolites to determine the effect of catalyst pore size and acidity on the reaction rate and catalyst fouling rate. The de-t-butylation rate over the original zeolites was mainly dependent upon their micro pore sizes. Although the dealumination by acid leaching decreased strong acid sites, the de-t-butylation rate over dealuminated HY zeolite was higher than that on the original zeolite. The present dealumination is a useful method to prepare an acid catalyst for de-t-butylation in a liquid-solid system.     

分子筛催化C_9芳烃脱烷基的研究

将Bi、Ni、Mo、Pt分别负载在氢型ZSM-5、MOR、Y分子筛上,以异丙苯为模型化合物对分子筛催化加氢脱烷基性能进行评价,考察了不同金属的活性和分子筛结构。结果表明,不同分子筛载体上,不同金属脱烷基活性大小次序为:Pt>Mo>Ni>Bi;分子筛的孔结构可限制产物的形成,从而影响烷基转移反应和脱烷基反应二者的活性。此外,酸强度和密度的分布与金属同样重要,它们之间的平衡协同作用对催化剂的活性有着至关重要的作用。     

An FT-IR study of the adsorption of aromatic hydrocarbons and of 2,6-lutidine on H-FER and H-ZSM-5 zeolites

The interaction of aromatic hydrocarbons benzene, toluene, o-, m- and p-xylene and of methyl pyridines (in particular 2,6-lutidine) with H-ZSM-5 and H-FER zeolites has been studied. Two different H-ZSM-5 samples with strongly different intensity ratios between the two main OH stretching bands have been used. Benzene, toluene and p-xylene enter easily the cavities and give rise to three different H-bonded complexes. Two of them are strongly bonded while the third is likely a very hindered and distorted one. o-Xylene enters slowly the cavities and m-xylene even more slowly. Faster diffusion occurs at higher temperatures. On the contrary, xylenes do not enter the FER cavities. In spite of its steric hindrance, supposed to be the same of m-xylene, 2,6-lutidine enters fast the ZSM channels and is protonated by the internal sites. On the contrary, it does not enter the FER cavities, but it is protonated too on the external silanols sites. Evidence is provided for some kind of heterogeneity of the internal sites of ZSM-5 zeolite. Additionally, it is concluded that other effects besides the molecular sieving effect may play a role in the access and diffusion of molecules into the zeolite channels.     

Sn改性Hβ分子筛催化顺酐酯化

采用离子交换法对Hβ分子筛进行骨架外Sn改性制得Sn-Beta分子筛,应用于顺丁烯二酸酐与正丁醇的酯化反应,并与Hβ分子筛进行对比。研究结果表明,Hβ分子筛的催化性能优于Sn-Beta分子筛,顺丁烯二酸酐转化率达98.0%,马来酸二丁酯产率达73.9%。采用X射线粉末衍射、N2物理吸附、傅里叶红外光谱、紫外-可见漫反射光谱和NH3程序升温脱附等技术对分子筛的物化性质进行表征,结果表明,Hβ分子筛比表面积大,孔容和孔径较大,酸量较多,有利于酯化反应的进行。     

Incorporation of vanadium into the mordenite structure by direct hydrothermal crystallization and secondary synthesis

The substitution of vanadium atoms into the zeolite framework structure could be applied to the large pore zeolites by means of modified treatments as well as direct hydrothermal synthesis. The incorporation of vanadium into the mordenite framework was demonstrated by XRD, FTIR, UV-Vis techniques and tested with catalytic oxidation reactions. These vanadium-containing zeolites have selective catalytic properties in the various oxidation reactions as compared with vanadia-impregnated catalysts.     

Isobutane/1-butene alkylation on LaNaY catalysts modified by alkali and alkaline-earth cations

The effect of incorporating alkali and alkaline-earth cations into La exchanged NaY zeolites on the alkylation of isobutane with 1-butene has been investigated. The strength of the acid sites of the LaMNaY (M = Group I A and Group II A elements) catalysts do not change significantly, while the density of acidic sites decrease in the order of Na > K > Rb > Cs in the alkali Group I A elements and Ba > Mg > Ca > Sr in the alkaline-earth Group II A elements. The LaBaNaY catalyst has a higher density of acid sites than expected based on the electronegativity of Ba among the Group II A elements . A higher yield of alkylation and oligomerization products and also a higher amount of carbonaceous deposit were observed on the LaMNaY catalysts with a lower density of acidic sites except for LaBaNaY . Thermal gravimetric and differential thermal analysis indicate that the carbonaceous material could be located on the pore mouth and inside the pores of the zeolite. The carbonaceous material on the pore mouth can be desorbed before 300°C, while that in the zeolite pore is more difficult to be removed and a series of reactions such as dehydrogenation, aromatization and polymerization may take place during a temperature-programmed oxidation process. The diffusion of oligomerization products from the zeolite pore appears to be a slow step. The accumulation of these products in the zeolite pores is believed to be the main factor for the catalyst deactivation.     

Esterification of oleic acid in soybean oil on zeolite catalysts with different acidity

The catalytic activity of zeolites was studied in the esterification of oleic acid with methanol in soybean oil. The influences of acidity and pore structure of the zeolites were investigated in relation to conversion of the oleic acid on the zeolite catalysts. H⁺ ion exchanged ZSM-5 (HMFI) and mordenite (HMOR) zeolites conducted with different Si/Al ratio were employed to examine an influence of acidity in the reaction. Conversion of oleic acid was about 80% on HMOR zeolites and HMFI(25) zeolite. The conversion of oleic acid was improved as the amount of acid site increased. The amount of acid site of the zeolites affected significantly the catalytic activity in the esterification of oleic acid.     

TUN, IMF and -SVR Zeolites; Synthesis, Properties and Acidity

The effect of synthesis conditions on the preparation and properties of three novel zeolites TUN, IMF, and -SVR was investigated and compared with MFI. X-ray powder diffraction, infrared spectroscopy, chemical analysis, sorption measurements, and scanning electron microscopy were employed to characterize the textural and chemical properties of these zeolites. FTIR spectroscopy in combination with pyridine as probe molecule was used to describe the type, concentration and acid strength of these zeolites. Zeolite -SVR was synthesized with Si/Al ratios higher than 100 in contrast with TUN and IMF having Si/Al ratios about 20–30, respectively. TUN, MFI and IMF zeolites exhibit similar concentrations of Brønsted and Lewis acid sites and also similar acid strength of Brønsted sites. In contrast, the presence of one vacancy/unit cell in the case of -SVR zeolite substantially changes its acidic properties. Generally, zeolites TUN and IMF exhibit similar acidic properties in terms of acid strength and Brønsted to Lewis acid site ratio like MFI and due to their slightly larger pores higher activities in catalytic reactions are expected.