Hierarchical Porous ZSM‐5 Zeolite Synthesized by in situ Zeolitization and Its Coke Deposition Resistance in Aromatization Reaction

Hierarchical ZSM‐5 zeolites with micro‐, meso‐ and macroporosity were prepared from diatomite zeolitization through a vapor‐phase transport process on solid surfaces. The aromatization performance of the catalysts was investigated on a fixed bed reactor by using FCC gasoline as feedstock. The crystal phase, morphology, pore structures, acidity and coke depositions of the hierarchical ZSM‐5 zeolites were characterized by means of X‐ray diffraction (XRD), scanning electron microscope (SEM), N₂ adsorption/desorption, Fourier transform infrared (FT‐IR) and thermogravimetry‐mass spectrogram (TG‐MS), respectively. The results show that the prepared hierarchical ZSM‐5 zeolite possesses excellent porosity and high crystallinity, displaying an improved aromatization performance and carbon deposition resistance due to its meso‐ and macroporous structures.     

碳四烃在改性HZSM-5分子筛上芳构化研究

研究了炼厂混合C_4烃在Zn、Ga、Cr、La改性的HZSM-5分子筛催化剂上的芳构化反应,采用TPD和IR测定了催化剂的表面酸性质。结果表明,用Zn(3%)和Zn(2%)Ga(1%)改性的HZSM-5分子筛具有较好的芳构化性能;各改性HZSM-5分子筛催化剂芳构化性能变化与表面酸性有关,总酸量下降,芳构化活性下降,强B酸中心减少,深度裂解反应减少;Zn的单组分和双组分改性的HZSM-5分子筛催化剂芳构化活性的增高与表面强L酸浓度增加和吡啶吸附IR谱中的1615cm~(-1)吸收峰出现有关。     

Synthesis of zeolite IM-5 under rotating and static conditions and the catalytic performance of Mo/H-IM-5 catalyst in methane non-oxidative aromatization

The hydrothermal crystallization of zeolite IM-5 was investigated under rotating (denoted as IM-5-R) and static (denoted as IM-5-S) synthesis conditions. Mo-modified catalysts (Mo-IM-5-R and Mo-IM-5-S) were prepared for the methane non-oxidative aromatization. The physical properties and acidities of the samples were characterized by XRD, SEM, BET and IR spectroscopy. Compared with Mo-IM-5-S, the Mo-IM-5-R catalyst showed both a higher conversion of methane and higher selectivity to benzene in methane aromatization. A higher catalytic activity of Mo-IM-5-R may be attributed to the preferable textural properties and acidities of zeolite IM-5-R. Moreover, the catalyst prepared by the physical mixing method exhibited lower initial activity, but better stability for methane aromatization than that prepared by the impregnation method.     

Selective conversion of methane to aromatic hydrocarbons on large crystallite zeolite catalysts with mesoporous structure

Large crystallite mesoporous MFI (ZSM-5) zeolite was synthesized by using carbon nano-powder as a secondary template. The surface properties, morphological and phase composition of the synthesized material and of the commercial ZSM-5 (Zeolyst) zeolite were studied by nitrogen porosimetry, XRD and scanning electron microscopy. The results showed that the volume of mesopores volume increases with development of a secondary mesoporosity in the structure of zeolite. The obtained zeolite supports were used to prepare molybdenum-containing catalysts for the methane aromatization by solid phase preparation technique. Based on the XPS data, molybdenum particles in these catalysts are characterized by more uniform size distribution. The formation of a secondary pore structure restrains the carbon deposit formation as well as increases the methane conversion and the yield of the aromatic compounds.     

Effect of the formation of secondary pores in zeolite ZSM-5 on the properties of molybdenum-zeolite catalysts for methane aromatization

A study is performed of 4% Mo/ZSM-5 (30) catalysts for methane aromatization prepared by solid-phase synthesis with mechanical mixing of a zeolite with MoO₃ followed by calcination at 550°C. Zeolite etched with sodium hydroxide solutions and dealuminated with aluminum nitrate solutions is used as a support. Catalytic studies of the catalysts are conducted. The effect of treating the initial zeolite on the properties of catalysts in methane aromatization is determined. The effect subsequently treating a zeolite support has on the acid sites of a catalyst is confirmed by means of temperature-programmed reduction and the temperature-programmed desorption of NH3. The formation of molybdenum ions in the +5 oxidation state during catalysis and the presence of graphitized carbon deposits on a spent catalyst’s surface are confirmed by EPR and temperature-programmed oxidation.     

Gemini quaternary ammonium salt cationic surfactant‐assisted hydrothermal synthesis: An effective way to tune the textural properties of zeolite and the acidity of Beta molecular sieves

Novel hierarchical Beta zeolites have been successfully synthesized via a one‐pot dual‐templates strategy utilizing gemini organic surfactant and tetraethylammonium hydroxide (TEAOH)through hydrothermal process. The influence of several parameters on the formation of hierarchical Beta zeolite, the change in acidity and a possible growth scheme were systematically investigated. The physicochemical properties of these catalysts were characterized by PXRD, BET, SEM, HRTEM SAED, TG and NH₃‐TPD techniques, and the performance as acid catalysts was verified using the transformation of EtOH as a model reaction. On one hand, WAXRD data indicated that decreasing the temperature of synthesis and increasing amounts of C_12‐6‐12 in the process of synthesis resulted in lower crystallinity of Beta zeolites due to the BEA nuclei formation and crystal growth constrained by C_12‐6‐12. On the other hand, SAXRD and HRTEM data evidenced that C_12‐6‐12 initially generated a pseudo‐ordered mesoporous phase which was then partially occupied by the zeolite. After a period of ~96 h for crystallization, the hierarchy zeolite possessing 765.7 m²·g^‐1 of Brunauer‐Emmett‐Tellerarea, and average mesopore size distribution of 3.51 nm can be synthesized, and its microporous structure has a good crystallinity and lower amounts of acid sites than that of the microporous Beta one. Furthermore, the as‐obtained hierarchical zeolite displayed lower deactivation rate mainly due to the less coke formation on the surface of catalyst. It is expected to develop more considerable potential application value for the hierarchical Beta zeolite structure in the near future.     

不同硅铝比两亲性HZSM-5沸石的制备和表征

 采用三甲基氯硅烷并通过控制水的添加量对硅铝比分别为25, 42和101的HZSM-5沸石进行外表面修饰,制得三种两亲性沸石样品. 水的添加量对沸石催化剂的两亲性有显著影响. 红外光谱和低温氮吸附等测试结果表明,两亲性沸石样品具有与各自母体沸石相似的酸性及略小的比表面积. 在环己烯水合及乙酸异戊酯水解的相界面反应中,两亲性沸石分布于水-油两相界面,并表现出明显高于各自母体沸石的催化活性. 硅铝比为42的两亲性HZSM-5样品表现出最佳的相界面催化性能. 相对于环己烯水合反应,两亲性HZSM-5沸石更适用于乙酸异戊酯水解的相界面催化反应.     

Effect of zeolite pore morphology on solvent-less alkylation of benzene with 1-hexene

In an attempt to convert the carcinogenic benzene which is almost restricted for its use in gasoline, alkylation reaction with olefin 1-hexene has been conducted on various zeolites. Four zeolites having different pore topology and pore size have been applied as solid acid catalysts for effective production of alkylate in a liquid phase, solvent-less low temperature reaction. The textural properties of all the four zeolites (ZSM-5, MOR, BEA, HY) have been characterized for crystal morphology by TEM, crystal structure by XRD and FTIR, BET for surface area, N₂ sorption for porosity and TPD for acidity. Among the zeolite, BEA possessed high surface area (600.61 m²/g) and enhanced meso pores volume (0.3956 cm³/g) as compared to other zeolite samples. The performance of BEA was also observed to be superior in the liquid phase alkylation of benzene with 1-hexene in a batch reactor under autogenous pressure without using any solvent. At the optimum reaction conditions, the benzene conversion was 86.6 wt% and 3-Phenylhexane, 2-Phenylhexane yield were about 47.9 wt% and 38.7 wt% respectively on this catalyst. The BEA also exhibited longer time-on-stream and reusability performance, thus offers an attractive route for converting benzene into valuable (3-Phenylhexane, 2-Phenylhexane) alkylate product useful for the manufacturing of fine chemicals, dyestuff, detergents and scents.     

Mo/HZSM-5丙烷芳构化催化性能及其吸附量热的研究

采用等量浸渍法制得一系列不同担载量的Ｍｏ／ＨＺＳＭ－５催化剂,运用ＸＲＤ和ＦＴＩＲ方法考察了Ｍｏ物种在催化剂表面的分散状态,首次采用微分吸一热技术对Ｍｏ／ＨｚＳＭ－５催化剂的表面酸性进行表征。同时研究了催化剂对丙烷芳构化的反应活性。结果表明：对于担载Ｍｏ的ＨＺＳＭ－５分子筛催化剂,Ｍｏ物种在ＨＺＳＭ－５分子筛表面上顺序为ＨＺＳＭ－５〉１％Ｍｏ／ＨＺＳＭ－５〉２％Ｍｏ／ＨＺＳＭ－５分子筛本身表面的酸     

La／HZSM—5催化剂上丙烷的芳构化反应研究

采用浸渍法和离子交换法制备了La/HZSM-5分子筛催化剂,用于丙烷芳构化反应,利用XRD,SPS,FT－IR,NH3－TPD技术考察了La对HZSM－5分子筛结构和表面酸性的影响,引入La后能显著提高HZSM－5的丙烷芳构化活性,其中由离子交换法得到的催化剂效果最佳,在反应温度550度,空速600h^-1条件下,丙烷转化率和芳烃选择性分别达到94．58％,68．99％,在La/HZSM-5中分子筛结晶度下降,B酸中心减少,L酸中心增多,离子交换法制备的催化剂比浸渍法催化剂的这种变化更显著,同时更有利于La3 进入分子筛孔道内,并与分子筛产生强相互作用,新增加的L酸中心可能是芳构化反应的活性中心。     

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.     

Fabrication of hierarchical ZnSAPO-34 by alkali treatment with improved catalytic performance in the methanol-to-olefin reaction

A series of hierarchical ZnSAPO-34 zeolites were synthesized by treatment with different concentrations of tetraethylammonium hydroxide (TEAOH) solutions. The synthesized samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), temperature-programmed desorption, Fourier transform infrared, and N₂ adsorption and desorption techniques and studied as catalysts for the methanol to olefin reaction. The characterization results reveal that the crystal size of ZnSAPO-34 is greatly reduced compared with the parent SAPO-34 owing to the incorporation of Zn. Hierarchical pores with the sizes up to the macropore level in the ZnSAPO-34 zeolites are created with the post-treatment of TEAOH. The acid strength and the amounts of the strong acid of the hierarchical ZnSAPO-34 zeolites decrease after the post-treatment because TEAOH preferentially extracts Si species from the zeolite. The hierarchical ZnSAPO-34 zeolites exhibit superior catalytic performance than that of the parent ZnSAPO-34, owing to the shortened transportation distance and the appropriate acidity of the treated samples.     

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.     

沸石载体结构对甲烷无氧芳构化性能的影响

考察了担载MoO₃的沸石催化剂上甲烷的无氧芳构化性能,并与沸石结构相关联.结果表明,孔径与苯分子动态直径相当的ZSM-5、ZSM-8、ZSM-11和β沸石等是甲烷无氧芳构化催化剂的良好载体,其中3%MoO₃/HZSM-11具有最高的甲烷芳构化活性和稳定性,973K下的转化率和苯选择性分别为8.0%和90.9%;6%MoO₃/HZSM-8与7%MoO₃/H-β芳构化性能相当.以HMCM-41和HSAPO-34为载体时芳构化活性很低,以HMOR、HX和HY为载体时仅有少量乙烯生成,而以HSAPO-5和HSAPO-11为载体时未检测到烃类生成.     

含镍Y沸石的硫化及加氢脱硫性能

本文制备了不同形态的含镍Y沸石, 研究了温度, 时间和H~2S浓度对含镍Y沸石硫化的影响, 发现负载型含镍Y沸石最易硫化, 离子交换型次之, 骨架型最难硫化。考察了沸石表面硫化物物种的热稳定性和水热稳定性。指出高温下沸石脱附的水蒸汽能使硫化物发生水解, 导致催化剂失硫。用XRD, IR和化学分析等方法对硫化的含镍沸石催化剂进行表征, 硫化后沸石表面形成的NiS~x有可能是属正交晶系的Ni~7S~6化合物。对噻吩加氢脱硫反应, 硫化的含骨架镍Y沸石无催化活性, 硫化的离子交换型含镍Y沸石活性比负载型含镍Y沸石高5-6倍左右, 因其酸性较强。催化剂表面酸性位和硫化镍活性位共存, 对噻吩加氢脱硫反应是有利的。     

Spectroscopic and XRD characterisation of zeolite catalysts active for the oxidative methylation of benzene with methane

The benzene methylation with methane over zeolite catalysts was previously shown in our laboratory to require the presence of oxygen. Thus, a two-step mechanism involving the intermediate formation of methanol by partial oxidation of methane followed by the methylation of benzene with methanol in the second step, was postulated. This paper now reports the results of the characterisation of the zeolite catalysts used for the oxidative benzene methylation reaction in order to provide some information about their composition, structure, properties and their behaviour before and after the reaction. The catalysts were characterised by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence (XRF), FT-IR and solid state NMR. XRD results indicate that the crystalline structures of all the ZSM-5 and H-beta catalysts remained unchanged after batch reaction of benzene with methane over the catalysts in agreement with the observation that the catalysts recovered from the reactor could be reused without loss of activity. Elemental analyses and FT-IR data show that as the level of metal ion exchange increases, the Br?nsted acid concentration decreases but this metal ion exchange does not totally remove Br?nsted acidity. FT-IR results further show that only a small amount of acid sites is actually necessary for a catalyst to be active since used catalysts containing highly reduced Br?nsted acidity are found to be reusable without any loss of their activity. 29Si and 27Al magic angle spinning (MAS) NMR together with FT-IR spectra also show that all the active zeolites catalysts contain some extra-framework octahedral aluminium in addition to the normal tetrahedral framework aluminium. The presence of this extra-lattice aluminium does not, however, have any adverse effect on the crystallinity of the catalysts both before and after oxidative benzene methylation reaction. There appears also to be no significant dealumination of the zeolite catalysts during reaction since their catalytic performance was retained after use.     

Effect of the nature of a structure-forming additive on the physicochemical properties of zeolites and the activity of Zn-containing catalysts based on them in ethane aromatization

The effect the nature of the structure-forming additive has on the physicochemical properties of synthesized zeolites and the activity of Zn-containing catalysts prepared on their basis in converting ethane into aromatic hydrocarbons is studied. It is shown that the structure-forming additive plays an important role in the hydrothermal synthesis of zeolites. It is found that the highest activity and stability in ethane aromatization is exhibited by a catalyst based on a zeolite synthesized using hexamethylenediamine as a template.     

Zinc-containing zeolite catalysts for ethane aromatization prepared by solid-state modification

Solid-state modification was used to prepare zinc-containing zeolite catalysts based on pentasils with different framework SiO₂/Al₂O₃ ratios. The catalysts were studied by X-ray diffraction analysis and IR spectroscopy. The activity and selectivity of the Zn—pentasil systems prepared by the solid-state modification and impregnation methods were compared in the aromatization of ethane. The active and stable zeolite catalysts modified by transition metal ions can be obtained by the topochemical method.     

晶粒大小对ZSM-5分子筛甲醇制低碳烯烃催化性能的影响

对三种HZSM-5分子筛进行Ca改性,获得两组酸性接近的催化剂,考察了晶粒大小对甲醇制低碳烯烃(MTO)反应的影响。通过进一步与Na改性的比较,探讨了Ca在催化反应中的作用。采用扫描电镜(SEM)测定晶粒大小及形貌,氨气程序升温脱附(NH3-TPD)及吡啶红外吸附(Py-IR)表征催化剂的酸性。MTO催化性能测定结果表明,HZSM-5的低碳烯烃选择性较低且下降较快,催化活性降低也快;Ca改性降低酸性,提高了低碳烯烃选择性和催化稳定性;晶粒大小主要影响催化稳定性,小晶粒分子筛催化剂稳定性更好。高Ca含量改性效果更好;钠改性也提高了低碳烯烃选择性,但其稳定性较差。对于HZSM-5和Ca/HZSM-5,小晶粒的催化剂具有较好的催化稳定性。提出Ca参与了催化反应,MTO是一个酸碱协同作用的催化过程。     

甲烷在含镓沸石（MFI）上无氧活化性能的研究

采用水热法合成了不同Ｓｉ／Ａｌ、Ｓｉ／Ｇａ比的含镍分子筛，催化反应活性表征结果表明，地丙烷芳构化反应具有良好催化活性的含镍分子。没有显示出任何催化甲烷芳构化反应的特性；ＭｏＯ３作为添加组分显著地改变了催化剂的反应性能，３％ＭｏＯ３负载的含Ｇａ分子筛，在９７３Ｋ温度给出了约６％甲烷转化率和大于８０％的芳烃选择性，与ＺＳＭ－５相比，城相同的ＭｏＯ３担载条件下，含Ｇａ分子筛催化剂甲烷芳构化活性较低，但是