Interaction between ammonium heptamolybdate and NH4ZSM-5 zeolite: the location of Mo species and the acidity of Mo/HZSM-5

Mo/HZSM-5 catalysts show high reactivity and selectivity in the activation of methane without using oxidants. Mo/HZSM-5 catalysts with Mo loading ranging from 0 to 10% were prepared by impregnation with an aqueous solution of ammonium heptamolybdate (AHM). The samples were dried at 393 K, and then calcined at different temperatures for 4 h. The interaction between Mo species and NH₄ZSM-5 zeolite was characterized by FT-IR spectroscopy, differential thermal analysis (DTA) and temperature programmed decomposition (TPDE) and NH₃-TPD at different stages of catalyst preparation. The results showed that if Mo/HZSM-5 catalysts were calcined at a proper temperature, the Mo species will interact with acid sites (mainly with BrØnsted acid sites) and part of the Mo species will move into the channel. The Mo species in the form of small MoO₃ crystallites residing on the external surface and/or in the channel, and interacting with BrØnsted acid sites may be responsible for the methane activation. Strong interaction between Mo species and the skeleton of HZSM-5 will occur if the catalyst is calcined at 973 K. This may lead to the formation of MoO ₄ ^2– species, which is detrimental to methane activation.     

Xylene isomerization by ZSM-5 zeolite catalyst

The larger pore LaY zeolite catalyst resembles homogeneous metal chloride and heterogeneous silica-alumina acid catalysts since the results are consistent with isomerization being a series of intramolecular 1,2 shifts. On the other hand, isomerization with the smaller pore zeolite, ZSM-5, is very different and the relative rate constants appear to be influenced by diffusion and/or shape selectivity. Disproportionation is a significant reaction with LaY but not with ZSM-5 in the temperature range used for the present study. The small amount of trimethylbenzene formed at low conversions using ZSM-5 is 1,2,4-trimethylbenzene, also providing evidence of shape selectivity influencing the reaction products.     

ZSM-5分子筛吸附去除VOCs的研究进展

挥发性有机化合物(VOCs)的治理已成为当前大气污染防治的主要方向,引起广泛关注。吸附法具有操作简单、工艺成熟、能耗低和效率高等优点,是脱除VOCs的有效方法。从治理VOCs方法出发,简述ZSM-5分子筛用作吸附剂在治理VOCs方面影响其吸附效率的主要因素,如硅铝比、掺杂金属阳离子、表面酸碱性及吸附状态等,为ZSM-5分子筛的性能优化及新品开发,提供理论依据。在总结现有的吸附工艺基础上,提出吸附法与其他技术的联用,是今后VOCs治理的主要发展方向。     

改性ZSM-5分子筛催化合成哌嗪

研究了不同金属离子改性得到的M-ZSM-5分子筛在以乙二胺(EDA)为原料合成哌嗪反应中的催化性能。通过NH3-TPD和BET法对催化剂进行表征,结果表明,经过离子交换后HZSM-5的骨架结构没有发生变化,仅仅是表面酸性发生了变化。重点考察了催化剂酸性对反应的影响,实验表明,提高弱酸和中强酸中心所占比例有利于哌嗪(PA)和三乙烯二胺(TEDA)生成。以Zn-ZSM-5和Zn/K-ZSM-5为催化剂,在常压,t=360℃,空速为0.25 g/(min.h),m(EDA)∶m(H2O)=4∶6的反应条件下,原料EDA的转化率分别为94.1%和82.6%;产物PA和TEDA的选择性分别为45.5%,42.1%和29.4%,50.1%。     

Diffusion and catalytic reaction in zeolite ZSM-5

Rates of reaction and product-distributions for small and large pellets and for small and large crystals of the same zeolite-preparation (H-ZSM-5) were observed in order to evaluate the influence of diffusion (concentration-gradients) on the conversion of (CH₃)₂O to hydrocarbons with this catalyst. Diffusivities of (CH₃)₂O and C₆H₆ in the zeolite crystals were obtained from sorption kinetics. Macropore-diffusion affects activity and selectivity if pellets with dia > 2 mm are used; intracystalline mass-transfer does not seem to be important with respect to catalyst-activity and selectivity at temperatures below 600 K. The conventional model of diffusion and reaction in porous catalysts can not be applied to the entire reaction-network in the zeolite-crystals, because migration of olefins in the zeolite can not be understood as random-walk diffusion.     

Cr掺杂ZSM-5双功能催化剂的制备及其催化裂解正丁烷

采用原位合成的方法制备了Cr掺杂的ZSM-5分子筛,研究了Cr含量对于正丁烷催化裂解性能的影响。利用X射线衍射（XRD）、N₂吸附脱附、紫外可见漫反射光谱（UV-Vis）、拉曼光谱（Raman）、氨程序升温脱附技术（NH₃-TPD）和吡啶红外（Py-FTIR）等表征手段研究了分子筛的结构、Cr物种的存在状态以及分子筛的酸性。研究结果表明,部分Cr进入分子筛的骨架,以单分散的形式存在,当Cr含量较低时,Cr的引入对于分子筛的弱酸性没有太大的影响。少量Cr的引入会极大提高正丁烷的转化率和乙烯、丙烯的收率,当Cr/Al摩尔比为0.04,反应温度为650℃时,正丁烷的转化率达到99.2%,乙烯、丙烯的收率达到53.8%,分别比未改性的ZSM-5高15.5%和5.0%。这可能是由于Cr活性组分的脱氢性能和分子筛的酸性形成协同作用,促进了正丁烷的高效转化。     

Catalytic and multinuclear MAS NMR studies of a thermally treated zeolite ZSM-5

Catalysts of ZSM-5 type were obtained by synthesis with tetrapropyl-ammonium-bromide (TPABr) as a template and subsequent hydrothermal treatment up to 1173 K. ¹H-, ²⁷Al-, and ²⁹Si-NMR spectroscopy and the direct oxidation of benzene with N₂O as a catalytic test were applied to characterize the products. ²⁷Al MAS NMR and ²⁷Al 3QMAS NMR studies of the samples give evidence that fivefold-coordinated extra-framework aluminum species exist if the product is treated at 1173 K and then rehydrated. The values of all characteristic catalytic key data are highest when the catalysts are precalcined at 1173 K. This is a clue that species giving rise to fivefold-coordinated aluminum species in the hydrated products are responsible for the high catalytic key data. The nature of these species is not yet clear. Two models for the species are in agreement with our experimental findings.     

ZSM-5型分子筛强化水吸收CO_2

在难溶气体吸收体系中加入第3分散相粒子是强化传质过程的一个重要手段,文中采用恒温搅拌釜对ZSM-5型分子筛/水浆料强化CO2的吸收过程进行了实验研究,考察了硅铝摩尔比(120,150,360)、固含率和气相CO2体积分数对增强因子的影响。结果表明:随着分子筛硅铝摩尔比的增加,其疏水性增强,增强因子随之增大;随着分子筛固含率的增加,气液界面处颗粒的覆盖率增大,增强因子迅速增大,当气液界面处颗粒的覆盖率逐渐接近最大覆盖率时,则增强因子逐渐趋于恒定值;随着气相CO2体积分数的增加,溶质在溶液中的扩散作用逐渐增强,而分子筛颗粒输运作用逐渐减弱,增强因子减小。针对分散相微粒增强难溶气体的吸收过程,提出了一个三维非均相传质模型,计算结果和实验数据吻合良好。     

ZSM-5沸石分子筛吸附模拟废水中对苯二酚的研究

以正硅酸乙酯为硅源、偏铝酸钠为铝源、四丙基氢氧化铵为模板剂,利用水热合成法制备ZSM-5沸石分子筛并将其应用到吸附水中对苯二酚的研究,考察了吸附时间、对苯二酚溶液pH值、吸附温度、吸附剂用量对吸附效果的影响。结果表明,最佳吸附条件是:吸附温度为35℃,吸附时间为60 min,对苯二酚溶液pH值为6,吸附剂用量为0.4 g。此时,对苯二酚的去除率最高,达到了68.28%。     

ZSM-5分子筛的合成与改性研究进展

ZSM-5分子筛是一种在石油催化裂化过程中常用的择型分子筛,具有良好的热稳定性、耐酸性和择型选择性。催化剂中ZSM-5分子筛的添加可以提高汽油辛烷值和烯烃产率。目前,中国已经形成了以催化裂化为主的重质油加工工艺,2013年原油加工量超过4亿t/a。在未来相当长一段时间,催化裂化加工重质劣质原料油仍是炼油厂的工作重点。综述了近年来国内外ZSM-5分子筛的合成与改性研究进展,为今后ZSM-5分子筛合成与改性方面的研究提供了一定的借鉴和参考。     

ZSM-5沸石合成与改性技术进展

ZSM-5沸石在石油化工过程中得到广泛应用。阐述了ZSM-5沸石的合成、改性技术现状及其应用以及近年来的研究和开发应用最新进展，为ZSM-5沸石的开发利用提供新的思路。     

利用高岭土合成ZSM-5沸石

对苏州高岭土的特性以及不同温度焙烧的高岭土结构变化进行了考察,以碱抽法确定其中的活性SiO2和活性Al2O3的含量,分别以有胺法(正丁胺)和无胺法合成得到较高相对结晶度的ZSM-5沸石,并对产物进行表征.结果表明,高岭土最佳焙烧温度为950℃,有胺法和无胺法合成的ZSM-5沸石相对结晶度分别达54.6%和53.3%,产...     

高岭土及ZSM-5沸石分子筛形貌表征

对高岭土及ZSM-5沸石分子筛扫捕电镜样品制备方法进行研究,用该方法对不同产地高岭土进行表征研究.结果表明.选用合适的分散方法对高岭土及合成分子筛进行处理后制备扫描电镜样品,能够有效提高扫描电镜图片清晰度;不同产地高岭土的呈现不同形貌特征.在某一产地的高岭土微球中合成ZSM-5沸石分子筛,考查不同晶化反应时间对ZSM-...     

超细ZSM-5分子筛的制备及其形貌表征

对比考察了模板剂的种类、晶化温度以及铝含量等影响因素对超细ZSM-5分子筛晶化行为的影响,采用扫描电镜（SEM）、透射电镜（TEM）和X射线衍射光谱（XRD）技术对所制备的超细产物的结构及形貌进行了表征。结果表明,模板剂的种类对分子筛的晶化过程有重要影响,四丙基氢氧化铵是优良的制备超细ZSM-5分子筛的模板剂;以四丙基氢氧化铵为模板剂,适宜采用静态法制备超细ZSM-5分子筛的晶化温度为70～ 120 ℃;凝胶体系中铝的存在抑制ZSM-5分子筛晶核的生长,无铝条件下,分子筛的晶化速度最快;随着铝含量的增加,分子筛的晶化速度变慢,在相同的晶化时间内,生成的分子筛的粒径更小。     

负载金属离子ZSM-5分子筛膜脱除苯并噻吩-二苯并噻吩的性能

采用水热合成法制备ZSM-5分子筛膜,并通过负载金属离子对其进行改性。通过X线衍射仪(XRD)、扫描电子显微镜(SEM)对所制备的膜进行表征。将所制得的ZSM-5分子筛膜经过负载金属离子改性后用于模拟汽油中苯并噻吩、二苯并噻吩二元硫化物的分离,考察负载离子种类、负载离子浓度和操作温度对二元硫化物竞争吸附和渗透通量的影响,并应用软硬酸碱理论(HSAB)分析吸附能力的强弱。结果表明:当Ag+浓度为0.2 mol/L时硫化物的分离因子最高可达1.31;随着操作温度的升高,ZSM-5分子筛膜渗透通量逐渐增大而分离因子逐渐减小。     

Organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite

A series of ZSM-5/ZSM-11 co-crystalline zeolites with various compositions and morphologies were successfully synthesized via an organic template-free hydrothermal route and characterized by XRD, XRF, SEM, NMR and N₂ adsorption/desorption technologies. The effects of raw materials and batch composition were investigated systematically. Various silicon sources can be employed in the organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite, however only a few types of aluminum sources are available. This organic template-free system is favorable to the aluminum-rich zeolite. With the increase of initial SiO₂/Al₂O₃ ratio, the ZSM-5 percentage in the ZSM-5/ZSM-11 co-crystalline zeolite increases as well as the crystal size, and especially the morphology of ZSM-5/ZSM-11 co-crystalline zeolite prepared from the colloidal silica-NaAlO₂ solution system changes gradually from nano-rod aggregation, micro-spindle to single hexagon and then to twinned hexagon crystals. Moreover, Na⁺ and OH⁻ in the initial materials can promote the nucleation of the ZSM-5/ZSM-11 co-crystalline zeolite significantly and are beneficial to the formation of crystals with relatively low length/width ratio, while K⁺ postpones the crystallization process seriously.     

ZSM-5 型沸石膜反应器在乙苯脱氢反应中的模式

引言 沸石分子筛膜是近些年发展起来的和种新型的膜分离技术[1],它是通过分子筛孔道实现分子筛分,从而得到较高的分离因数.     

Mn and Zn doped ZSM-5 zeolite catalysts

Manganese was incorporated into a ZSM-5 zeolite by a special impregnation method which practically prevented the deposition of the metal ions on the internal surface of the zeolite pores. As a result, the production of light olefins increased sharply while that of aromatics did not significantly change. The double incorporation of Zn (by ion-exchange) and of Mn (by this impregnation technique) led to catalysts which could produce more aromatics and more light olefins (mainly ethylene and propylene) than the parent ZSM-5 zeolite.     

磷镁改性的ZSM-5分子筛催化性能研究

研究了磷、镁改性对ZSM-5分子筛的孔结构和酸性的影响。采用甲苯的歧化反应为探针反应,考察了改性后分子筛催化甲苯选择歧化反应的活性和选择性。结果表明,磷、镁单独改性时,随着负载质量分数的增加,转化率逐渐增加,且大于相同工艺条件下HZSM-5的转化率。当磷质量分数达到3％～5％ 或镁质量分数达到1％时,转化率达到最大值,这时对二甲苯为平衡组成,基本没有选择性。磷镁复合改性时,既可以提高催化剂的选择性,又可以使催化剂的活性不至于降得很低。在磷质量分数为9％、镁质量分数为1％时,改性效果最好。     

Kinetics of sorption of aromatics in zeolite ZSM-5

The kinetics of sorption of benzene, p-xylene and o-xylene into crystals of zeolite ZSM-5 in the hydrogen form were investigated gravimetrically for well-defined constant boundary conditions and constant temperature (298 K) of the sorbent. Zeolite crystals were mounted on aluminium foil separated in space, the metal foil acting as sample holder and heat sink in the exothermic sorption process. The influence of crystal size on the rate of sorption was studied by comparing two samples of the zeolite differing only in crystal size.

Sorption of benzene into ZSM-5 follows a pattern expected on the basis of the diffusion equation with constant diffusivity. p-Xylene is sorbed initially faster than benzene; its rate of sorption decreases at higher degrees of loading where a hysteresis loop in the isotherm is observed. Sorption of o-xylene proceeds much more slowly than that of p-xylene and does not seem to be controlled by diffusion.