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。     

Microstructure of a Pd/ceria–zirconia catalyst after high-temperature aging

Ga/ZSM-5 is an effective catalyst for the conversion of dilute (3%) ethylene-in-methane reactant streams into aromatic hydrocarbons at 500–550°C. A Ga loading as low as 0.5 wt% is sufficient to obtain maximum yields of aromatic products. At 520°C, an ethylene conversion of 93%, with an aromatics selectivity of 81%, was obtained over a 5 wt% Ga/ZSM-5 catalyst. The conversion of ethylene into aromatics over Ga/ZSM-5 catalysts involves a complex sequence of oligomerization, isomerization, cracking, and cyclization reactions that occur on Brønsted acid zeolites in the zeolite. The role of the gallium, which exists as both Ga³⁺ at zeolitic exchange sites and as Ga₂O₃ within the channels and on the external surface of the calcined catalyst, is to promote dehydrogenation of the acid-catalyzed oligomerization and cyclization products.     

Zn-ZSM-11 zeolite catalyst for LPG aromatization

LPG transformation into aromatic hydrocarbons using Zn²⁺ modified pentasil zeolites has been studied at 450–540 °C and 10–58 g h/mol. The conversion and selectivity to aromatics obtained over Zn-H-ZSM-11 catalysts with different degree of exchange suggest, the primary role of the Zn²⁺ species is in C-H activation and the transformation of the intermediates into aromatic hydrocarbons.     

Perspectives of Micro/Mesoporous Composites in Catalysis

This article covers the recent development in the remarkably growing field of synthesis, characterization and particularly catalytic investigation of zeolite-based materials combining micro- and mesoporous features. New synthetic approaches for preparation of micro/mesoporous composites including recrystallization of originally amorphous matter, utilization of nanocrystalline zeolite seeds and formation of mesoporous zeolite single crystals are the first focus of this article. The advantages and disadvantages of composite materials in comparison with pure micro- and mesoporous molecular sieves will be discussed, as well. The relevance of individual experimental techniques for analysis of the composites, i.e., their structure, porosity, chemical composition, morphological features, and so on, are described in the second section of the article. The last Section is focused on the application of micro/mesoporous composites and mesoporous zeolites as catalysts in acid-catalyzed reactions, oxidation reactions and synthesis of fine chemicals. The potential of the composites in challenging areas of catalysis for future applications is the final objective of the review.     

用于芳烃中微量烯烃脱除的MCM-22催化剂的研究

考察了用氯化铵离子交换处理的MCM-22分子筛催化剂在脱除芳烃中微量烯烃的催化活性,对分子筛催化剂进行了表征.结果表明离子交换增加了催化剂固体酸中心的量,而第2次离子交换的MCM-22分子筛催化剂脱烯烃效果最佳,其固体酸中心的量为最大.失活的分子筛催化剂通过焙烧再生处理,可恢复其活性.     

多级孔沸石分子筛在芳烃烷基化反应中的研究进展

多级孔沸石分子筛不仅具有微孔沸石固有的高水热稳定性和强酸性,且兼具介孔以及大孔材料的传质优势,提高了表面活性位的有效利用率,在多相催化领域表现出良好的催化性能。本文详细阐述了近年来多级孔沸石在芳烃烷基化反应中的研究进展,讨论了多级孔沸石分子筛中介孔的存在对芳烃烷基化特别是其中包含有较大分子参与的烷基化催化反应的促进作用,从分子扩散和可接近性两方面解释了多级孔沸石对催化活性、选择性和稳定性的促进作用。同时指出制备具有高度有序结构的介孔沸石,并深入研究多级孔沸石的酸性,建立沸石酸性能、孔结构与催化性能之间的关联是未来多级孔沸石的研究方向。     

Ethane to Aromatic Hydrocarbons: Past, Present, Future

Ranking high in the current challenges of catalysis, direct transformations of lower saturated hydrocarbons (alkanes) have been investigated for a long time. However, unsaturated hydrocarbons (e.g., aromatics and olefins) have always been the more important feedstocks to produce basic and intermediate chemicals because of their wide variety of possible reaction pathways. This article focuses on the conversion of one representative of lower alkanes—ethane, which is an important constituent of natural gas, accompanying gases and waste effluents of petrochemical processes—to aromatic compounds.

Following general considerations on the aromatization of ethane, efficient modification methods of MFI-type zeolites to obtain active and selective catalysts will be presented. The nature of active sites, including the promoting effects of zinc, gallium, or noble metals, will be discussed. Single pathways in the reaction network from ethane toward aromatic hydrocarbons are explored based on experiments under steady-state and transient-state conditions. Finally, an outlook for possible transformations of the fundamental knowledge to full-scale industrial application will be given.

A meandering ethane river flows beneath a line of bluffs on Titan. Methane fog blankets the lowlands beyond to the horizon. Attempts to glimpse Titan's surface from Earth-bound observatories and interplanetary probes have been thwarted by the thick hydrocarbon haze that covers the moon at all times. [1]     

Sorption Accompanied by Chemical Reaction on Zeolites

The importance of zeolites as catalysts hardly needs to be emphasized. In the recent past the research activity in this area registered a noticeable increase after the discovery of ZSM-type zeolites. A single-step conversion of methanol into a mixture of hydrocarbons, predominantly in the gasoline range, would have been considered highly improbable before this discovery. Apart from their unusual shape selectivity, the low coking character of these zeolites is of particular importance to industrial practice. The discovery has clearly demonstrated promise for further research on the synthesis of new types of zeolites and exploration of novel reactions on zeolite catalysts. The exponential increase in research activity [68, 220] observed over the last 10 years is evidence of worldwide recognition of the potential of zeolite catalysts.     

Sorption Accompanied by Chemical Reaction on Zeolites

The importance of zeolites as catalysts hardly needs to be emphasized. In the recent past the research activity in this area registered a noticeable increase after the discovery of ZSM-type zeolites. A single-step conversion of methanol into a mixture of hydrocarbons, predominantly in the gasoline range, would have been considered highly improbable before this discovery. Apart from their unusual shape selectivity, the low coking character of these zeolites is of particular importance to industrial practice. The discovery has clearly demonstrated promise for further research on the synthesis of new types of zeolites and exploration of novel reactions on zeolite catalysts. The exponential increase in research activity [68, 220] observed over the last 10 years is evidence of worldwide recognition of the potential of zeolite catalysts.     

Mesoporous zeolite single crystal catalysts: Diffusion and catalysis in hierarchical zeolites

During the last years, several new routes to produce zeolites with controlled mesoporosity have appeared. Moreover, an improved catalytic performance of the resulting mesoporous zeolites over conventional zeolites has been demonstrated in several reactions. In most cases, the mesoporous zeolites exhibit higher catalytic activity, but in some cases also improved selectivity and longer catalyst lifetime has been reported. The beneficial effects of introducing mesopores into the zeolites has in most instances been attributed to improved mass transport to and from the active sites located in the zeolite micropores. Here, we briefly discuss the most important ways of introducing mesopores into zeolites and, for the first time, we show experimentally that the presence of mesopores dramatically increases the rate of diffusion in zeolite catalysts. This is done by studying the elution of iso-butane from packed beds of conventional and mesoporous zeolite catalysts. Moreover, we discuss in detail the recent observation of improved activity and selectivity in the alkylation of benzene with ethene using mesoporous zeolite single crystal catalysts. For this reaction, we show by calculation of the Thiele modulus that this improved performance can be mainly attributed to a diffusional limitation of ethylbenzene in the zeolite pores. This is verified in new ethylbenzene dealkylation experiments where mesoporous zeolite catalysts show significantly improved activity over conventional zeolite catalysts.     

芳烃长链烷基化催化工艺研究进展

芳烃长链烷基化是一类重要的有机合成反应,在化工生产中具有广泛的应用价值。传统催化工艺所采用的氢氟酸等催化剂具有高腐蚀、高污染的特点,难以满足化工行业环境友好的发展需求。本文指出固体酸、离子液体两大类催化剂是实现该工艺绿色化转型的关键所在,并综述了固体酸、离子液体两大催化体系的研究成果、应用现状及主要技术问题。研究表明二者对于芳烃长链烷基化均具有较高的活性及选择性,以固体酸为催化剂的Detal工艺已然实现工业化生产。但目前两种催化剂均存在易失活的问题,且Detal工艺的运行成本较高,因而未来需开展有关研究提高催化剂的稳定性、降低工艺的能耗及物耗以缩减运行成本。     

Translating clean liquid fuels synthesis with low aromatics over NaFe@C/HZSM-22 directly in CO2 hydrogenation

Fuel production is an option for valorizing CO₂, yet deficient catalysts meeting the standard fuel production has impeded progress of this promising technology. Herein, liquid fuel synthesis is rationalized over a catalyst consisting ‘C′, ‘Na’, and ‘Fe’, as in NaFe@C, configured with ZSM-22 and ZSM-5 in CO₂ hydrogenation. While the ‘Na’ and ‘C′ functioned as structural promoters on Fe to enhance CO₂ conversion and olefins synthesis, the characteristics of the zeolites facilitated oligomerization of lighter hydrocarbons. A high C₅ + selectivity was obtained over the HZSM-22 composite in CO₂ hydrogenation dominated by olefins and isoparaffins. Model reactions for exemplar oligomerization activity over the zeolites revealed ZSM-5 as highly active with selectivity towards isoparaffins and aromatic. The ‘Na’ cations induce Lewis’s acid sites (LAS) which suppresses hydrocracking during chain growth. This consistency, revealed between the model and CO₂ hydrogenation unlocks a door to zeolite usage in CO₂ hydrogenation to clean heavy hydrocarbons.     

过渡金属/分子筛催化剂上选择性催化还原氮氧化物的研究进展

综述了近十年来过渡金属/分子筛催化剂上氨和碳氢化合物选择性催化还原NOx方面的研究进展。在NH3-SCR体系,着重介绍了铜基和铁基分子筛催化剂的研究状况,探讨了分子筛催化剂在该体系中的失活原因;在HC-SCR体系,总结了不同过渡金属、分子筛类型、还原剂、H2O和SO2等对催化剂活性的影响,探讨了目前比较公认的碳氢化合物选择性催化还原NOx的反应机理。最后展望了分子筛催化剂在选择性催化还原NOx领域今后的研究方向。     

Zeolite catalysis studied by radiolysis/EPR. Transformations of cyclic olefins

The Brønsted acid-catalyzed transformations of cyclic olefins in zeolites HZSM5 and H-mordenite were elucidated by the radiolysis/EPR method. Products of catalytic reactions were spin- labeled by radiolytic means and identified by using EPR spectroscopy. Comparison of reactions on HZSM5 and H-mordenite reveals strong shape selectivity on reactions in these catalysts. The radiolysis/EPR method is a new in situ spectroscopy with excellent sensitivity and structural specificity for the study of reaction mechanisms in zeolite catalysts.     

甲醇气相脱水制二甲醚催化剂研究进展

甲醇气相脱水制二甲醚反应为固体酸催化反应,常用的固体酸催化剂有γ-Al₂O₃和分子筛类。γ-Al₂O₃表面存在弱酸中心或中等强度酸中心,催化剂有较好的初始催化活性,但活化所需的反应温度较高,耐水稳定性差;分子筛类催化剂表面有许多强酸性位,低温下催化活性较高,但在高温反应条件下易产生烃类副产物和积炭,热稳定性差。为改善这两类催化剂的催化性能,对催化剂进行了各种改性研究,改性后催化剂的活性、选择性和稳定性均有一定程度提高。综述了近年来在γ-Al₂O₃和分子筛催化剂上进行的改性研究,总结并展望了甲醇脱水催化剂的发展方向。     

介孔结构和助剂Zn对不同晶粒大小ZSM-5催化甲醇制芳烃 反应性能的影响

通过碱处理和添加助剂Zn对微米ZSM-5和纳米ZSM-5进行改性,获得具有不同孔结构和酸性质的催化剂。采用氮气吸附、X射线衍射、透射电镜、氨气程序升温脱附（NH₃-TPD）和热重（TG）技术对不同催化剂进行表征,结合催化性能评价,考察晶粒尺寸、介孔结构和Zn助剂对其催化甲醇制芳烃（MTA）反应性能的影响。结果表明,碱处理引入介孔后,孔体积均增大,总酸量都降低;微米催化剂外表面积显著增加,但纳米催化剂外表面积却有所下降;负载金属Zn后,比表面积、结晶度和总酸量都降低。在P=0.5MPa、T=430℃、WHSV=2h^-1的反应条件下,负载Zn的微米催化剂由于具有较高的酸量,其芳烃与苯、甲苯和二甲苯（BTX）选择性最高,分别为85.11%和66.85%,但是稳定性较差,催化寿命仅为12h。但相较于未改性的纳米ZSM-5原粉来说,碱处理后又负载Zn的催化剂,液烃中芳烃选择性从纳米原粉的65.20%增加到80.82%,BTX选择性从纳米原粉的42.30%提高到49.56%,而在甲醇进样量增加4倍,即WHSV=8h^-1时,催化剂仍显示出较好的稳定性,寿命可达84h。可见,在小晶粒ZSM-5上碱处理扩孔并引入Zn助剂可以有效提高甲醇制芳烃反应性能。     

Solid-state NMR for metal-containing zeolites: from active sites to reaction mechanism

Metal-containing zeolite catalysts have found a wide range of applications in heterogeneous catalysis. To understand the nature of metal active sites and the reaction mechanism over such catalysts is of great importance for the establishment of structure-activity relationship. The advanced solid-state NMR (SSNMR) spectroscopy is robust in the study of zeolites and zeolite-catalyzed reactions. In this review, we summarize recent developments and applications of SSNMR for exploring the structure and property of active sites in metal-containing zeolites. Moreover, detailed information on host-guest interactions in the relevant zeolite catalysis obtained by SSNMR is also discussed. Finally, we highlight the mechanistic understanding of catalytic reactions on metal-containing zeolites based on the observation of key surface species and active intermediates.     

A quantum-chemical study of hydride transfer in catalytic transformations of paraffins on zeolites. Pathways through adsorbed nonclassical carbonium ions

A quantum-chemical investigation of the hydride transfer reaction in catalytic transformations of hydrocarbons on zeolites has been performed. Ab initio calculations at the MP2/6-31++G^**//HF/6-31G^* level demonstrated that the activated complexes of hydride transfer reaction in catalytic transformations of paraffins on zeolites very much resemble adsorbed nonclassical carbonium ions. However, these transient species are strongly held at the surface active sites by the Coulomb interaction. The calculated activation energies for reactions involving propane and isobutane are in a reasonable agreement with the experimental data. This revised version was published online in July 2006 with corrections to the Cover Date.