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。     

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.     

Methanol-to-Olefin Conversion over Zeolite Catalysts: Active Intermediates and Deactivation

Methanol-to-olefin (MTO) conversion over various zeolites with different topologies, Si/Al molar ratios, and crystallite sizes were investigated to verify the effects of pore shape and size, acidity, and external surface area on the catalytic activity, product selectivity, and deactivation. The IR and electron spin resonance (ESR) study of zeolite catalysts used in MTO also proceeded to deduce the active intermediates formed in their cages or pores. The zeolites with 8 membered-ring (MR) pore entrances such as CHA, ERI, LTA, and UFI commonly exhibited high selectivity to lower olefins due to their small entrances, but the CHA catalyst with the smallest cage maintained its activity longer than other 8MR zeolites. The slow condensation of polymethylbenzene (PolyMB) to polyaromatic hydrocarbons (PAH) on MOR zeolite with a high Si/Al molar ratio due to its low concentration of strong acid sites resulted in a slow deactivation. The extremely small crystallites of H-SAPO-34 and H-ZSM-5 less than 100 nm showed an adverse effect in MTO; while the large crystallites above 1,000 nm also exhibited poor catalytic performance because of their small external surface. The study of IR regarding the adsorbed and occluded materials on zeolites demonstrated the effect of pore shape and size on the active intermediates: the zeolites with larger pores and cages allowed the formation of alkylbenzenes with long alkyl groups which preferred to be condensated to PAH. The well-resolved hyperfine splitting of ESR spectra observed on H-SAPO-34 used in MTO clearly illustrated the presence of hexamethylbenzenium radical cations. The small intersections of phosphorous-modified H-ZSM-5 allowed the formation of tetramethylbenzenium radical cations in MTO. The formation of PolyMB radical cations, their role as active intermediates and the effect of topology, acidity, and crystallite size of zeolites on their deactivation were discussed.     

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.     

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.     

Selective acetylation of toluene to 4-methylacetophenone over zeolite catalysts

The vapour phase acetylation of toluene has been catalysed by acidic H-ZSM-5, H-mordenite and REY zeolite catalysts at 453 K in a tubular reactor at atmospheric pressure. H-ZSM-5 exhibited the best results during the reaction with respect to rate of acetylchloride conversion (TOF=7.5 mol s⁻¹ mol⁻¹ Al×10⁻⁴), conversion of acetyl chloride (60.2 wt.%) and selectivity for 4-methylacetophenone (88.3%) compared to both H-mordenite and REY zeolites. It is revealed that the activity and selectivity of the catalyst strongly depend on the acidic properties and pore openings of the zeolites, respectively. It is observed that isomer ratio (4-methylacetophenone/2-methylacetophenone) is influenced by the reaction conditions and type of zeolite used in the reaction. With increasing reaction temperature and toluene to CH₃COCl molar ratio, the conversion of CH₃COCl (ACT) increases, while it decreases with the increase in reaction time, weight hourly space velocity (WHSV), Na-content and silica to alumina molar ratio of H-ZSM-5 in the acetylation of toluene. H-ZSM-5 is deactivated under the reaction conditions.     

π-Interactions between Cyclic Carbocations and Aromatics Cause Zeolite Deactivation in Methanol-to-Hydrocarbon Conversion

The understanding of catalyst deactivation represents one of the major challenges for the methanol-to-hydrocarbon (MTH) reaction over acidic zeolites. Here we report the critical role of intermolecular π-interactions in catalyst deactivation in the MTH reaction on zeolites H-SSZ-13 and H-ZSM-5. π-interaction-induced spatial proximities between cyclopentenyl cations and aromatics in the confined channels and/or cages of zeolites are revealed by two-dimensional solid-state NMR spectroscopy. The formation of naphtalene as a precursor to coke species is favored due to the reaction of aromatics with the nearby cyclopentenyl cations and correlates with both acid density and zeolite topology.     

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.     

用于乙烯芳构化反应的Zn/HZSM-5催化剂失活机制研究

采用浸渍法制备了Zn负载量（质量分数）分别为1%、2%、3%的Zn/HZSM-5分子筛催化剂,通过XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR、XPS、TG-DTA等技术,系统考察Zn/HZSM-5分子筛在乙烯芳构化反应的失活机制。结果表明,积炭是催化剂失活的主要原因,HZSM-5中Zn的添加在较大程度上抑制了催化剂的积炭行为;低Zn含量时催化剂失活缓慢,但Zn含量较高时,由于催化剂比表面积和孔体积极剧下降,催化剂失活加剧。反应过程中,分子筛上Zn物种存在迁移和流失行为,迁移行为体现为催化剂表面Zn的富集和相对比例的变化;Zn流失速率在不同反应阶段保持恒定,但受到Zn含量的影响,Zn含量越高、流失速率越大。外表面ZnO是分子筛催化剂Zn流失的主要物种,且随Zn负载量升高变化趋势愈加明显,其含量与积炭速率存在一定关联。     

Effect of combining the metals of group VI supported on H-ZSM-5 zeolite as catalysts for non-oxidative conversion of natural gas to petrochemicals

The most prestigious catalyst applied in natural gas (methane) non-oxidative conversion to petrochemicals is 6%Mo/H-ZSM-5.Chromium,molybdenum and tungsten are the group VI metals.Hence,in this work,6%Mo/H-ZSM-5 was correlated with 3%Cr+3%Mo/H-ZSM-5 and 3%W+3%Mo/H-ZSM-5 as catalysts to examine their promoting or inhibiting effects on the various reactions taking place during methane conversion.The catalytic activities of these catalysts were tested in a continuous flow fixed bed reactor at 700℃ and a GHSV of 1500 ml·g-1 ·h-1. Characterization of the catalysts using XRD,TGA and TPD were investigated.XRD and NH3-TPD showed greater interaction between the W-phase and the Bronsted acid sites in the channels of the zeolite than between Cr-phase and the acid sites in the zeolite.     

H-ZSM-5分子筛不同孔道处的酸位在甲醇制烯烃反应中的催化作用

甲醇制烯烃(MTO)作为一条由煤、天然气和生物质等含碳资源制备重要有机化学品的非石油路线,近年来备受关注.作为MTO催化剂,分子筛的骨架拓扑结构和酸性质对于其催化活性、反应路径和产物分布等具有重要的影响.H-ZSM-5分子筛是一种典型的MTO反应催化剂,酸位可以分布在MFI拓扑结构的直孔道、正弦孔道和交叉位点处.虽然目前已普遍认可MTO反应遵循芳烃/烯烃双循环烃池机理,分子筛的催化性能与其骨架中酸中心的位置相关,但对于H-ZSM-5分子筛不同孔道位置处的酸中心在甲醇制烯烃反应中的催化作用仍缺乏足够认识.本文采用密度泛函理论计算和分子动力学模拟方法,对H-ZSM-5分子筛不同孔道处(包括正弦孔道、直孔道和交叉腔)酸位中心上的MTO反应网络(包括芳烃循环、烯烃循环和芳构化)及甲醇原料和烯烃/芳烃产物的扩散行为进行了比较研究.结果表明,与正弦孔道和直孔道相比,芳烃循环和芳构化反应在交叉腔的酸中心上因具有较低的能垒而更易进行.相比之下,在正弦孔道和直孔道中,多甲基苯的生成受到显著限制,而烯烃循环却可以在三种酸中心(正弦孔道、直孔道和交叉腔)上以相近的能垒和相似的几率进行.芳烃循环生成乙烯和丙烯的几率相近,而烯烃循坏产物以丙烯和较高的烯烃产物为主.落位于H-ZSM-5交叉腔的酸中心能促进芳烃中间体如多甲基苯的生成,推动芳烃循环,提高乙烯选择性,而正弦孔道和直孔道中的酸中心则能增强烯烃循环,生成较多的丙烯和较高的烯烃产物.因此,H-ZSM-5分子筛对MTO的催化性能(包括活性和产物选择性等),可以通过有目的地调节酸中心在分子筛骨架中的位置分布(即铝落位)而得到有效调变和提升.本文阐明了H-ZSM-5分子筛酸中心在MTO反应中的催化作用与其骨架中的落位之间的有机联系,为高效甲醇转化分子筛催化剂的设计和性能提升提供了参考思路.     

Dimethylether production on zeolite catalysts activated by Cl-, F- and/or ultrasonication

The chlorinated and fluorinated zeolite catalysts were prepared by the impregnation of zeolites( H-ZSM-5,H-MOR or H-Y) using two halogen precursors( ammonium chloride and ammonium fluoride) in this study. The influence of ultrasonic irradiation was evaluated for optimizing both halogen precursors for production of dimethylether( DME) via methanol dehydration in a fixed bed reactor. The catalysts were characterized by SEM,XRD,BET and NH3-TPD. The reaction conditions were temperatures from 100 to 300 ℃ and a WHSV = 15. 9 h-1. All halogenated catalysts showhigher catalytic activities at all reaction temperatures studied. However, the halogenated zeolite catalysts prepared under ultrasonic irradiation showhigher performance for DME formation. The chlorinated zeolite catalysts show higher activity and selectivity for DME production than the respective fluorinated versions.     

RUB-13分子筛的合成及其甲醇制烯烃催化性能

采用水热法合成RUB-13分子筛，探讨了有机模板剂（OSDA）、硅源、晶化温度和水硅比等制备条件对RUB-13分子筛晶体结构的影响，考察了RUB-13分子筛在甲醇制烯烃（MTO）反应中的催化性能。结果表明，采用1，2，2，6，6-五甲基哌啶（PMP）为有机模板剂、白炭黑为硅源，在晶化温度为170℃的条件下，选择H₂O/Si比为100和80时可分别合成出高纯度的低硅铝比（Si/Al=100）和高硅铝比（Si/Al=200）的RUB-13分子筛晶体，且晶粒呈棒状形貌。H-Al-B-RUB-13（Si/Al=200）分子筛用于催化甲醇制烯烃反应时，在400℃下表现出高的低碳烯烃选择性（C_2-5⁼选择性达97.8%，丙烯选择性为54.5%），优于传统的H-SAPO-34和H-ZSM-5分子筛催化剂。     

Role of adsorption in zeolite-catalyzed hydrocarbon cracking reaction

The activity for hydrocarbon cracking of zeolite catalysts depends on the type of zeolite and steam treatment. By comparing the activities of different zeolites under the condition where the catalyst did not undergo deactivation and the product distributions were identical, and presumably for the monomolecular mechanism, it was found that there were no differences in the chemical properties of the active sites in the zeolites. The apparent differences in catalytic activities among zeolites could be attributed to different concentrations of adsorbed alkane reactants, which is a consequence of the different strength of interaction of the alkyl groups with the zeolite walls. The latter may also be a significant contribute to the observed different strengths of interaction of alkyl amines with the Brønsted acid sites in zeolites.     

Stability of ZSM-11 and BETA zeolites during the catalytic cracking of low-density polyethylene

The stability of H-ZSM-11 (H-Z) and H-BETA (H-B) zeolites during the catalytic degradation of low-density polyethylene (LDPE) was studied using the same sample of catalyst in eleven consecutive cycles. The gaseous hydrocarbons, liquid hydrocarbons and waxes generated in each cycle were analyzed as well as the used catalyst. The zeolites were characterized by XRD, FTIR of adsorbed pyridine and N₂ adsorption, while the physical mixtures of LDPE/zeolites were subjected to TG-DTG analysis.The H-Z zeolite exhibited an important stability during the successive cycles of LDPE conversion. On the contrary, the behavior H-B zeolite was completely different; from the sixth cycle the yields of products changed progressively, approaching to that obtained in a purely thermal process.The yields of accumulated coke increased steadily throughout the cycles up to maximum values in the eleventh cycle of ∼6 and ∼15 wt% for H-Z and H-B, respectively. These results were confirmed by TG under air flow.     

The effect of acidity behaviour of Y zeolites on the catalytic degradation of polyethylene

Thermogravimetric (TGA) and differential scanning calorimetric (DSC) analyses were used to investigate the effect of the acidity behaviour of Y zeolites on the catalytic degradation of polyethylene (PE). The acidity behaviour of these zeolites was modified by ion exchange treatments. Two Y zeolites with similar Si/Al atomic ratios were subjected to an ion exchange treatment using NaNO₃ for H-form (HY) and NH₄NO₃ for Na-form (NaY). The activity and the deactivation behaviour of the Y zeolites were determined in the samples by TGA measurements, using a polymer/catalyst ratio of 9:1. The sample residues obtained after an isothermic TGA, were analysed by DSC, in order to evaluate the crystallinity of each mixture. The HY zeolite, which has the strongest acidity, reduced the onset temperature resulting in more rapid degradation of the polymer. It is shown that the ion exchange treatment over Y zeolites enhances the selective catalytic degradation of polymer in detriment of the rapid deactivation.     

Influence of the ZSM-5 Support Acidity on the Catalytic Performance of Pd/ZSM-5 in Lean Methane Oxidation

Although zeolites are characterized by their special acidic properties, there is still no clear consensus on the effect of zeolite support acidity on the catalytic activity of supported Pd catalyst in methane oxidation. Herein, a series of Pd/H-ZSM-5 and Pd/Silicalite-1 catalysts was prepared by the deposition-precipitation method and used in lean methane oxidation. The effect of ZSM-5 support acidity on the catalytic performance of Pd/ZSM-5 was investigated. The results indicate that with the decrease of Si/Al ratio(x), viz., the increase of acid sites in H-ZSM-5(x), the catalytic activity of Pd/H-ZSM-5(x) increases substantially; the activity of various catalysts in the lean methane oxidation decreases in the order of Pd/H-ZSM-5(28)>Pd/H-ZSM-5(48)>Pd/H-ZSM-5(88)>Pd/H-ZSM-5(204)>Pd/Silicalite-1. Furthermore, various characterization measures reveal that the catalytic activity of Pd/H-ZSM-5(x) in lean methane oxidation is mainly related to the Lewis acid sites in the H-ZSM-5 support, whereas less relevant to the Brønsted acid sites. The abundant Lewis acid sites in H-ZSM-5 are capable to enhance the interaction between the Pd species and H-ZSM-5 support, which can inhibit the agglomeration of Pd particles and improve the dispersion of Pd species, and thus boost the catalytic activity of Pd/H-ZSM-5 in methane oxidation.     

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.     

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.     

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。