小孔沸石微结构的CO_2吸附表征

以3种已知结构的小孔沸石3A、4A和5A为研究对象,以N2和CO2为吸附质,通过吸附数据测定,研究了小孔沸石微孔结构的吸附表征方法.结果表明,N2吸附无法检测4A沸石的孔,而CO2吸附可以检测.对于4A和5A沸石,在35s内CO2吸附就可以达到平衡.HK(Horvath-Kawazoe)柱状模型不能表征4A和5A沸石的孔结构,但是HK球形模型可以,基于最大吸附量、D-A(Dubinin-Astakhov)方程和Langmuir-Freundlich模型计算了4A和5A沸石的微孔孔容,其中根据最大吸附容量和D-A方程计算的微孔孔容与文献值最接近.     

苯在酸碱处理多级孔Y分子筛上的吸附及传质行为

利用H_4EDTA-NaOH共处理的方法制备了具有不同孔径分布的多级微-介孔NaY分子筛。运用XRD、N_2吸附、SEM、TEM对其结构进行了表征。采用频率响应(FR)和智能重量分析仪(IGA)技术研究了苯在改性后的多级孔NaY分子筛及微孔NaY分子筛上的吸附和传质性能。结果表明,适当的酸碱处理不会改变分子筛的晶体结构,但可调变NaY分子筛的精细结构;介孔的引入降低了分子在孔道中的扩散阻力,较大的孔径和较好的孔道贯通性有利于扩散和吸附中心的可接近性;对于微孔NaY分子筛,苯在分子筛上的吸附过程为其传质过程的速控步骤,对于酸碱处理的多级孔NaY分子筛,分子筛颗粒中微/介孔内的扩散过程及分子筛微-介孔孔道间的分子交换过程是传质过程的速控步骤。     

氩吸附法研究多级孔分子筛的孔结构

采用不同方法分别制备了双介孔分子筛、介微孔分子筛及介孔沸石材料,利用氩吸附法并结合XRD技术表征了多级孔分子筛的孔结构。探讨了适用于多级孔分子筛的孔径分布计算方法,揭示了不同类型吸附等温线与孔径分布、孔型及孔容等之间的关系。研究表明,对于多级孔分子筛、微孔和介孔的孔径分布分别用SF法和BJH法计算较适宜,全孔分析可用NLDFT法计算。通过对TS-1介孔沸石的孔结构分析发现, TPAOH 在改性制备介孔TS-1的过程中起到了生成介孔及促进二次晶化的双重作用。     

多级孔ZSM-5分子筛对低阶煤流化床快速热解产物分布的影响

采用晶种诱导法和碱处理法制备了不同介-微孔复合结构的多级孔ZSM-5分子筛,利用XRD、TEM、NH3-TPD、氮气物理吸附等手段对其结构性质进行了表征,并考察了其对低阶煤流化床快速热解产物分布的影响.结果表明,碱处理后不同程度上增加了分子筛催化剂的比表面积、介孔孔容和平均孔径.多级孔ZSM-5分子筛促进了热解挥发分中...     

分子筛对葡萄糖淀粉酶的吸附性能研究

测定了黑曲霉葡萄糖淀粉酶(E.C.3.2.1.3)在三种改性的、具有中孔和大孔的分子筛上的吸附等温线并将吸附量和吸附等温线的形状与分子筛的等电点、孔容、孔径及酸性相关联。讨论了孔结构和不同酶吸附量对分子筛固定化葡萄糖淀粉酶活力的影响。发现葡萄糖淀粉酶在再造孔分子筛上的单层饱和吸附量与再造孔的方法密切有关,三种不同再造孔方法制得的分子筛具有不同的骨架Si/Al比、不同的孔分布和比表面积。不同的Si/Al比导致不同的酸性质和等电点。酶吸附量与载体的表面酸性、等电点以及吸附时溶液的pH有关。分子筛对酶的吸附以静电作用为主。其次,当中孔孔径和孔容越大时,单层饱和吸附量亦越大。随着分子筛对葡萄糖淀粉酶的吸附量增加,固定化酶的活力增大,但固定化酶的比活力随吸附量的增加、中孔孔容和孔径的减小而下降。     

有序介孔炭的合成及液相有机大分子吸附性能研究

分别采用有序介孔氧化硅SBA-15和NaY分子筛为硬模板合成了系列有序介孔炭OMC和微孔炭CFY. N₂静态吸附测试表明, 所合成的介孔炭具有丰富的介孔结构和集中的介孔分布. 以亚甲基蓝为探针分子, 研究其在有序介孔炭OMC和微孔炭CFY上的吸附行为. 研究结果表明, 有序介孔炭中大于3.5 nm的大介孔孔容是决定亚甲基蓝吸附容量和吸附速率的关键因素. 吸附动力学理论研究表明, 准二级动力学方程可以很好地描述亚甲基蓝分子在介孔炭上吸附动力学行为.     

多孔活性炭孔径分布的表征

总结了利用气体吸附法表征多孔活性炭中孔和微孔孔径分布的各种方法。BJH方法和MP模型忽略了微孔内势能叠加效应,仅适合描述中孔孔径分布;HK模型和以Dubinin填充理论为基础的各种方法,考虑了微观下势能叠加的效果,在一定程度上能很好地描述微孔孔径分布;最近围绕GAI(GeneralizedAdsorptionIsotherm)而展开的利用密度范函理论(DFT,densityfunctiontheory)和巨正则系综蒙特卡罗(GCMC,grandcanonicalensemblemontecarlo)模拟确定微孔孔径分布的方法较好地克服了Dubinin理论中存在的缺点,是较好的两种方法,但其有效性还需要更多的实验结果来证明。     

浸渍金属盐二次活化制备中孔沥青基球形活性炭的研究

以煤焦油沥青为原料,水蒸气活化法制备具有一定孔隙结构的预活化沥青基球形活性炭:通过在预活化球形活性炭中浸渍Fe(NO3)3、Co(NO3)2、Ni(NO3)2水蒸气二次活化,制备得到具有不同中孔孔径分布和较高强度的球形活性炭;研究了金属Fe、CO、Ni在二次活化过程中对预活化球形活性炭的孔结构参数和VB12吸附性能的影响,实验结果表明,预活化球形活性炭通过浸渍硝酸盐二次活化能够有效提高中孔孔容和中孔含量,其中浸渍CO(NO3)2二次活化对中孔孔容的增加最为明显,其中孔孔容达0.50cm3/g,占总孔孔容的65%.随着浸溃Co(NO3)2二次活化时间的延长,预活化球形活性炭中孔孔容增加,孔径分布变宽.     

乙炔在ZSM-5分子筛上的吸附机制及吸附态性质

 在有微量水存在下研究了乙炔在HZSM-5和NaZSM-5上的吸附和脱附. 在80 ℃下, NaZSM-5上乙炔的饱和吸附量约为HZSM-5上的5倍,但在200 ℃以上时吸附的乙炔只有少量可存留于NaZSM-5表面. 这与乙炔在HZSM-5上的较强吸附显著不同. 依据FT-IR对乙炔吸附态的测定,研究了乙炔在ZSM-5分子筛上的吸附机制及吸附态性质. 乙炔与HZSM-5中B酸中心上的水作用形成乙烯醇,后者在升温时变为碳正离子结合在分子筛的 Al-O--Si 上构成强吸附物种. 在NaZSM-5上,乙炔只通过与Na+位上的水作用形成乙烯醇,后者与沸石孔道中的阳离子以静电结合构成弱吸附物种. 与HZSM-5的情况不同, NaZSM-5上的吸附物种在升温过程中被活化前即分解成乙炔脱附.     

孔道型微孔和介孔分子筛的改性及超级绝热性能

在水热体系中合成了具有规则孔道结构的微孔分子筛ZSM-5和介孔分子筛MCM-41,SBA-15,MAS-5,通过改变材料表面的电性对介孔材料进行了化学修饰.采用X射线衍射(XRD)和扫描电子显微镜(SEM)对样品的结构、形貌进行了表征;通过氮气吸附-脱附测试了产物的比表面积,采用BJH法计算孔分布和孔容;将制得的样品压制成绝热材料后,进行导热性质测定.常温(25℃)常压下,有序介孔分子筛MCM-41的导热系数为0.038 W·m-1·K-1,具有少量微孔结构的MAS-5的导热系数为0.035W·m-1·K-1,二者均为超级绝热材料.材料经改性后,绝热性能有所提高:MCM-41的导热系数降至0.028 W·m-1·K-1,MAS-5的导热系数降至0.017 W·m-1·K-1.结合纳米介孔材料导热理论模型进行分析,发现纳米孔绝热材料的孔径越小,孔隙率越大,绝热性能好;介孔分子筛的导热系数与其孔壁厚度、孔径大小以及孔隙率有关.     

亚硝胺在沸石上催化分解的研究

采用气相色谱 质谱（GC MSD）、程序升温表面反应（TPSR）和红外光谱（IR）技术研究吡咯烷亚硝胺（NPYR）和二甲基亚硝胺（NDMA）等亚硝胺在NaY、HY、NaZSM 5、HZSM 5等沸石上的催化分解,并剖析其产物分布,发现亚硝胺在Na＋型沸石上的裂解产物近似于热裂解,而在H＋型沸石上则发生了质子参与的催化裂解反应.     

Gadolinium(III)-loaded nanoparticulate zeolites as potential high-field MRI contrast agents: relationship between structure and relaxivity

The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd3+-loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH4)2SiF6 or diluted HCl resulted in materials that, upon loading with Gd3+, had a much higher relaxivity than the corresponding non-dealuminated materials. Analysis of the 1H NMR dispersion profiles of the various zeolites showed that this can be mainly ascribed to an increase of the amount of water inside the zeolite cavities as a result of the destruction of walls between cavities. However, the average residence time of water inside the Gd3+-loaded cavities did not change significantly, which suggests that the windows of the Gd3+-loaded cavities are not affected by the dealumination. Upon calcination, the Gd3+ ions moved to the small sodalite cavities and became less accessible for water, resulting in a decrease in relaxivity. The important role of diffusion for the relaxivity was demonstrated by a comparison of the relaxivity of Gd3+-loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd3+-doped zeolites are comparable in magnitude to the longitudinal ones at low magnetic fields (<60 MHz). However at higher fields, the transversal relaxivities steeply increased, whereas the longitudinal relaxivities decreased as field strength increased. Therefore, these materials have potential as T1 MRI contrast agents at low field, and as T2 agents at higher fields.     

Gamma‐Ray Irradiation to Accelerate Crystallization of Mesoporous Zeolites

Gamma‐ray (γ‐ray) irradiation was introduced into zeolite synthesis. The crystallization process of zeolite NaA, NaY, Silicalite‐1, and ZSM‐5 were greatly accelerated. The crystallization time of NaA zeolite was significantly decreased to 18 h under γ‐ray irradiation at 20 °C, while more than 102 h was needed for the conventional process. Unexpectedly, more mesopores were created during this process, and thus the adsorption capacity of CO₂ increased by 6‐fold compared to the NaA prepared without γ‐ray irradiation. Solid experimental evidence and density function theory (DFT) calculations demonstrated that hydroxyl free radicals (OH*) generated by γ‐rays accelerated the crystallization of zeolite NaA. Besides NaA, mesoporous ZSM‐5 with MFI topology was also successfully synthesized under γ‐ray irradiation, which possessed excellent catalytic performance for methanol conversion, suggesting the universality of this new synthetic strategy for various zeolites.     

Gamma-Ray Irradiation to Accelerate Crystallization of Mesoporous Zeolites

Gamma-ray (γ-ray) irradiation was introduced into zeolite synthesis. The crystallization process of zeolite NaA, NaY, Silicalite-1, and ZSM-5 were greatly accelerated. The crystallization time of NaA zeolite was significantly decreased to 18 h under γ-ray irradiation at 20 °C, while more than 102 h was needed for the conventional process. Unexpectedly, more mesopores were created during this process, and thus the adsorption capacity of CO₂ increased by 6-fold compared to the NaA prepared without γ-ray irradiation. Solid experimental evidence and density function theory (DFT) calculations demonstrated that hydroxyl free radicals (OH*) generated by γ-rays accelerated the crystallization of zeolite NaA. Besides NaA, mesoporous ZSM-5 with MFI topology was also successfully synthesized under γ-ray irradiation, which possessed excellent catalytic performance for methanol conversion, suggesting the universality of this new synthetic strategy for various zeolites.     

Technetium removal from the aqueous solution using zeolites A and Y containing transition metal ions Co2+ and Zn2+

Journal of Radioanalytical and Nuclear Chemistry - The adsorption properties of two zeolite types, faujasite (NaY, ZnY, CoY) and LTA-4A zeolite (NaA, ZnA, CoA), towards technetium were studied in...     

高温合成NaY沸石

提出了应用NaY沸石导向剂提供全部硅源合成NaY沸石的新方法, 研究了高温条件下合成NaY沸石的规律和特点, 发现在高温条件下合成NaY沸石不仅晶化速度快, 而且可以在不加有机物的条件下合成较高硅铝比[n(SiO2)/n(Al2O3)=6]的NaY沸石.     

(NaZSM-5)-AgI主体-客体纳米复合材料的研究

Silver iodide nanoclusters were successfully prepared in the channels of NaZSM-5 zeolite by a thermal diffusion method. Chemical analysis, powder X-ray diffraction, nitrogen adsorption technique, and infrared spectroscopy were used to characterize the prepared samples. The solid diffuse reflectance absorption spectra and luminescence properties were studied. Chemical analysis showed that the guest silver iodide was incorporated into the host NaZSM-5. Powder X-ray diffraction analysis showed that the framework of NaZSM-5 still remained in the (NaZSM-5)-AgI samples. Infrared spectra indicate that the vibration of the framework of NaZSM-5 had little variation attributable to the encapsulation of AgI in the host. This phenomenon is due to the incorporation of silver iodide into NaZSM-5. Investigation of the absorption revealed that the guest silver iodide was encapsulated in the channels of NaZSM-5. Solid diffuse reflectance absorption spectra indicated that the absorption of prepared (NaZSM--5)-AgI host-gust samples had nothing with the host NaZSM-5. The absorption spectra of the (NaZSM-5)-AgI samples were influenced by the size of AgI nanoclusters. Luminescence investigation showed that the prepared samples had a high energy band gap and a strong radiation process. The (NaZSM-5)-AgI samples are luminescient composite materials.     

Microscopic and macroscopic characterization of organosilane-functionalized nanocrystalline NaZSM-5

Nanocrystalline NaZSM-5 zeolites with systematically varied particle sizes (15, 60, and 200 nm) were functionalized with organosilanes. Through the systematic variation of particle size and therefore external surface area of NaZSM-5, the extent of functionalization and location of functional groups were spectroscopically verified. 29Si magic-angle spinning (MAS) NMR and Fourier transform infrared (FTIR) spectroscopy provided conclusive evidence that the silanol groups located on the external surface of NaZSM-5 were functionalized through reaction with the organosilanes. The 29Si NMR results provided quantitative information about the extent of functionalization on NaZSM-5. A nitroxide spin label was adsorbed on the external surface of NaZSM-5 to probe the surface properties by electron paramagnetic resonance (EPR) spectroscopy. The macroscopic and microscopic properties, such as the behavior of functionalized NaZSM-5 in different solvents, and the specific surface areas were also investigated. The hydrophobicity of the functionalized NaZSM-5 was found to increase relative to the parent NaZSM-5 as expected for an organic surface coating.     

Effects of zeolites and external magnetic field on photochemistry of arylmethyl esters and arylmethyl sulfones

The photolyses of benzyl p-methylphenylacetate (BCO₂A), 1-naphthyl phenylacetate (ACO₂N), p-methylbenzyl benzyl sulfone (ASO₂B) and 1-naphthyl benzyl sulfone (ASO₂N) were carried out on the pentasil and faujasite zeolites. The product distribution, in terms of the cage effect, was extremely sensitive to zeolite structure. Photolyses of BCO₂A and ASO₂B adsorbed on NaZSM-5 produce AB as the main product. In contrast, photoirradiation of ACO₂N and ASO₂N adsorbed on NaZSM-5 only gives AA and NN as the products, and the cage effect is essentially-100%. All the four substrates adsorbed on NaY zeolite show higher cage effects in the photolysed products compared with those in homogeneous solutions. All the observations are interpreted by consideration of size and shape sorption selectivity of the substrate molecules on the zeolite surface and restriction on diffusional motion of the photogenerated radicals imposed by zeolite surface. Application of a weak external magnetic field in the photolysis decreases the cage effects in all cases, which demonstrates that the reactive states for the photocleavage reaction of the esters and sulfones mainly involve triplet excited states.     

Synthesis,characterization and CO2 adsorption of NaA,NaX and NaZSM-5 from rice husk ash

NaA, NaX and NaZSM-5 zeolites were prepared by using silica extracted from rice hull ash as a raw material, and they were investigated for CO₂ adsorption performance as an adsorbent in order to solve the problem of suppressing the global warming. Three zeolites were synthesized by hydrothermal methods with seed technology, and a series of characterization methods, including XRD, FTIR, nitrogen adsorption-desorption and SEM, were used to demonstrate their advantages compared to traditional hydrothermal methods. The maximum equilibrium adsorption capacity of NaA-RS, NaX-RS and NaZSM-5-RS was 1.46, 3.12 and 2.20 mmol/g at 0 °C and 101.3 kPa, respectively. The CO₂ and N₂ adsorption isotherms recorded at different temperatures were perfectly fitted by the Dual-site Langmuir model. The CO₂/N₂ selectivity and Henry's law constants were calculated to demonstrate that the samples have a stronger affinity for CO₂, especially at low pressures. The isosteric heat of CO₂ and N₂ adsorption of the three zeolites was calculated, which was indicated that they were in an excellent potential for adsorption and separation of CO₂ in industrial flue gas.