BrØnsted acidity in HY zeolites measured by IR study of pyridine adsorption: influence of steric effects

The formation of pyridinium ions upon pyridine sorption on HY samples of varying Al composition has been studied by IR spectroscopy. It is demonstrated that HY supercages cannot accommodate more than four pyridinium ions. This property is shown to affect the ability of LF protons to migrate towards positions accessible to pyridine and form pyridinium ions. The mode of interaction of LF hydroxyls with pyridine is discussed in the light of both steric and electrostatic parameters.     

NO adsorption on Cu-ZSM-5: assignment of IR band at 2133 cm−1

The adsorption of nitrogen oxides on Cu-ZSM-5 was studied by infrared spectroscopy to elucidate the species associated with the band at 2133 cm^–1. The band was found for both NO and NO₂ adsorption. Labeling experiments with¹⁵NO revealed that the associated surface species contained nitrogen and, most likely, an N-O bond. Co-adsorption experiments of NO and oxygen produced adsorbed nitronium, NO ₂ ⁺ , as the principal, associated species. Adsorption of nitrogen oxides on dispersed CuO and the HZSM-5 support demonstrated that the 2133 cm^–1 band was not necessarily associated with copper ions. A relatively strong correlation between the bands at 2133 and 3615 cm^–1 indicates that the primary adsorption sites of NO ₂ ⁺ are the strongly protic, bridging Si(OH)Al framework hydroxyls. Once these were filled, other, weaker acid sites began to adsorb NO ₂ ^O .     

Stoichiometric adsorption complexes of boron trichloride and antimony pentafluoride in H-ZSM-5

This work demonstrates that inorganic metal halide compounds such as BCl₃ and SbF₅ can be used to prepare adsorption complexes with a stoichiometry of one molecule per Brønsted acid site in the zeolite H-ZSM-5. BCl₃-acid site complexes are prepared by saturating the zeolite with BCl₃ and then evacuating. The BCl₃complex desorbs above 400 K, and ~ 50% of the BCl₃ remains adsorbed at temperatures above 750 K. SbF₅-acid site complexes are prepared by saturating the zeolite, evacuating, and heating to 700 K in vacuum. The SbF₅ complex is shown to polarize coadsorbed acetone to the same degree as magic acid. The stability of the metal halide complexes is further characterized with adsorption and reaction of propene and ethene to for moligomers. Small amounts (<10%) of the metal halide desorb during the oligomer desorption experiment.     

Method for distinguishing Brønsted-acid sites in mixtures of H-ZSM-5, H-Y and silica-alumina

We have examined the adsorption and reaction of ethylamine, isopropylamine, 2-ethylhexylamine, cyclooctylamine, and diphenylethylamine on H-ZSM-5, H-Y, and silica-alumina samples using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA). Each of the amines decomposes at Brønsted-acid sites to alkene and ammonia products above 550 K by a reaction similar to the Hofmann elimination reaction, so that the number of molecules which decompose can be used to measure the number of acid sites in the sample. For H-ZSM-5, the concentration of sites determined using ethylamine and isopropylamine was approximately equal to the framework aluminum concentration; however, adsorption of cyclooctylamine and 2-ethylhexylamine in H-ZSM-5 was limited so that only a fraction of the sites were counted using these probe molecules. For the silica-alumina and H-Y samples, the concentrations of Brønsted-acid sites could be determined using ethylamine, isopropylamine, 2-ethylhexylamine, or cyclooctylamine; and the site concentrations determined in this way were essentially dependent of which amine was used. 2,2-Diphenylethylamine adsorption was limited on both silica-alumina and H-Y samples, but a much higher fraction of the Brønsted-acid sites on the silicaalumina sample could be counted. These results indicate that TPD-TGA measurements with various amines can be used to determine the concentration of Brønsted-acid sites in each of the components of a fluid-catalytic-cracking catalyst.     

对硝基氯苯在HZSM-5沸石中的吸附和扩散行为研究

通过静态吸附实验,研究水体中对硝基氯苯在HZSM-5沸石中的吸附和扩散行为.研究结果表明,对硝基氯苯在HZSM-5沸石中的吸附等温线存在2个平台,其最大吸附量与温度无关.对硝基氯苯优先吸附在沸石孔道的交点位置,其吸附过程由内扩散控制.对硝基氯苯在HZSM-5沸石中的扩散性与温度和对硝基氯苯的吸附量密切相关,其扩散系数在高温与吸附量小于2 mol/u.c.时较高.     

水在ZSM-5型分子筛中吸附的Monte Carlo模拟

构建了ZSM-5型分子筛物理模型,采用Connoly表面方法和Solvent表面方法对ZSM-5型分子筛的几何结构和性质进行了模拟分析。通过巨正则系综蒙特卡罗方法(GCMC)模拟研究了水蒸气在ZSM-5型分子筛上的吸附特性。通过模拟方法看到了实验难以表征的水蒸气在分子筛中具体吸附位,研究了压力、温度和硅铝比对ZSM-5型分子筛吸附性能的影响及其吸附热的变化规律。     

ZSM-5沸石分子筛吸附模拟含铬废水的研究

本论文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六价铬的研究,考察了吸附时间、铬酸钾溶液pH值、吸附剂用量、吸附温度对吸附效果的影响。结果表明,最佳吸附条件是:吸附剂的使用量为0.5g,铬酸钾溶液pH值为5,吸附时间为60 min,吸附温度为30℃,此时,六价铬的去除率最高,达到了93.46%。     

一种特殊结构沸石分子筛的物化及催化性能研究

以三乙醇胺为模板剂, 采用静态晶化水热法合成出一种特殊结构的沸石分子筛 (称作SAO-25) , 合成过程中不易发生混晶和转晶, 重复性良好。对SAO-25 沸石进行了物相分析和红外光谱研究, 考察了它的吸附性能和酸性。在SAO-25 沸石分子筛上进行正构烷烃 (n2-C6) 裂解反应测试, 显示出较高的催化活性; 在重油裂解反应测试中, 显示出很高的C=3、C=4 轻烯烃选择性。     

The effect of dehydration conditions on the adsorption and diffusion of propane and nitrogen in linde 5A zeolite

Diffusion of propane and nitrogen in small crystals (3.6 μm) of zeolite 5A has been studied by conventional uptake rate measurements. The zeolite crystals were subjected to various pre-treatments prior to propane and nitrogen adsorption. It is concluded that surface degradation due to pre-treatment is not believed to occur to a significant extent since it has been observed that after a proper regeneration of the adsorbent, the diffusional properties of the system have been restored. It is suggested that the Ca⁺⁺ cations which may initially obstruct the windows of the sieve become increasingly mobile with increasing sorbate concentration and move to sites within the cage. The results are broadly consistent with the study on the diffusional transition in zeolite NaX (Tezel et al., 1983).     

Characterization of acidic property of sulfo-group functionalized microporous and mesoporous silica by adsorption microcalorimetry

Sulfo-group functionalized microporous and mesoporous silica based-on a MCM-41 framework which showed solid acid property were synthesized and characterized by adsorption microcalorimetry. Both the sulfo-functionalized microporous and mesoporous silica (Micro-SO₃H and Meso-SO₃H) were prepared by the oxidation of thiol group (–SH) included mesoporous silica which was obtained through the hydrolysis and co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS). The samples have an ordered two-dimensional hexagonal pore array similar to that of MCM-41 as depicted from the XRD patterns. Nitrogen adsorption also shows that both microporous and mesoporous silica have pore characteristics similar to MCM-41, i.e. high surface area and high pore volume. However, pore regularity, surface area and pore volume decreased as the MPTMS loading increased. Solid-state ²⁹Si NMR indicated that the sulfo groups were successfully incorporated into both microporous and mesoporous silica frameworks. This sulfo-functionalized porous silica have high NH₃ uptakes and high differential heats of NH₃ adsorption, suggesting the presence of strong acidic sulfo groups on the silica surface. Acid catalyses of the samples were characterized by the isomerization reaction of but-1-ene to cis, trans-but-2-ene.     

1H broad-line and MAS NMR: application to the study of acid sites of desilicated zeolite ZSM-5

Broad-line¹H NMR study of desilicated zeolite ZSM-5 was carried out as a function of the number of adsorbed water molecules in amounts lower than or equal to that of the Brønsted acid sites. The dissociation coefficient of the acid OH groups, currently associated with the acid strength, was shown not to be affected by the selective removal of Si from the zeolite ZSM-5 framework which resulted in more Brønsted acid sites per unit surface area. On the other hand, by using MAS NMR, bridging Brønsted acid sites hydrogen-bonded to the zeolite framework were identified on the anhydrous surface of the desilicated ZSM-5. Moreover, MAS NMR spectra of the desilicated zeolite partially rehydrated showed the presence of some Lewis acid sites.     

Direct observation of carbon nanotube formation in Pd/H-ZSM-5 and MoO3/H-ZSM-5 based methane activation catalysts

The nature of carbonaceous species deposited upon MoO₃/H-ZSM-5 and Pd/H-ZSM-5 based catalysts during methane activation at 700 °C has been studied. TEM evidences the formation of open-ended multi-walled carbon nanotubes on MoO₃/H-ZSM-5 based dehydroaromatisation catalysts. Pd/H-ZSM-5 is more active, exclusively towards methane cracking and post-reaction analysis reveals the distribution of different carbonaceous species is more homogeneous which TEM demonstrates to be in the form of closed-end multi-walled carbon nanotubes.     

Pyridine adsorption reveals high-coordinated cationic centres at the surface of microcrystalline ZnO

The adsorption of pyridine at 300 K on microcrystalline ZnO has been investigated by FTIR spectroscopy. Besides an interaction by H-bonding with surface OH groups, evidence is found for the Lewis coordination of pyridine onto coordinatively unsaturated surface Zn²⁺ centres possessing a regular tetrahedral coordination, as well as onto some other surface Zn²⁺ centres, only slightly uncoordinated. The creation at the surface of the ZnO of cationic centres with an anomalous coordination higher than 4 (quasi-octahedral) is thus postulated. No such high-coordinated Zn²⁺ centres seem to form to an appreciable extent when ZnO is dispersed (at least at up to a 3% weight level) at the surface of other microcrystalline oxides such as, for instance, TiO₂.     

Ethylbenzene disproportionation and p-xylene selectivity enhancement in xylene isomerization using high crystallinity desilicated H-ZSM-5

Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered.Desilication was assessed through XRF,XRD,FTIR,TEM,nitrogen adsorption/desorption,NH_3-TPD,~(29)Si and~(27)Al MAS NMR analytical techniques.Desilication was accompanied with the creation of super acid sites.There exists a limit(Si/Al molar ratio of9.67)for keeping high crystallinity and obtaining improved catalytic performance.Desilication promotes ethylbenzene conversion by disproportionation and trans-alkylation reactions while the same reactions are limited for the xylene isomers.The p-xylene approach to equilibrium improves by more than 7% at 400℃ and a WHSV of 2 h~(-1)for the optimum sample with respect to the parent zeolite.At the same conditions,the optimum sample exhibits the maximum ethylbenzene conversion of 89%,i.e.more than 40%w.r.t.of the parent zeolite.However,the xylene yield decreases only 3%.     

疏水硅沸石吸附1,3-丙二醇的研究

FX-Ⅱ型沸石对1,3-丙二醇单组分溶液中1,3-丙二醇的静态饱和吸附量达到121.1 mg/g;在1,3-丙二醇和甘油的混合溶液中,研究了甘油质量浓度、吸附时间、吸附温度和盐离子质量浓度对1,3-丙二醇吸附的影响,实验结果表明高的甘油质量浓度对1,3-丙二醇吸附影响较大,吸附时间为14 h时1,3-丙二醇吸附达到平衡,低温及低盐离子质量浓度有利于1,3-丙二醇吸附;对实际发酵液的静态吸附结果表明,增大发酵液pH值可以减少有机酸对1,3-丙二醇的竞争吸附;pH值为7时,1,3-丙二醇吸附量达到102.5 mg/g;筛选了与吸附剂相关的脱附剂,用体积分数50%的乙醇解吸,解吸率达到86%。在此基础上初步研究了沸石对发酵液中1,3-丙二醇的动态吸附,1,3-丙二醇解吸率为82%。与传统的蒸馏法相比,沸石吸附法工艺简单,具有较大的研究和应用前景。     

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。     

C4烷烃在ZSM-5分子筛和Y分子筛上的吸附和扩散研究

采用气相色谱法研究了正丁烷和异丁烷在ZSM-5分子筛和Y分子筛上的扩散性能。烃分子的吸附平衡常数随温度的升高而降低，而扩散系数随温度的升高而增大。研究发现，烃分子的有效分子直径和分子形状是决定其扩散快慢的主要因素，同时分子筛孔道的大小对烃分子的扩散也存在影响，分子筛孔道越大，烃分子的扩散越快。     

基于沸石ZSM-5的CH4/N2/CO2二元体系吸附平衡

采用Rubotherm磁悬浮天平测量CH₄、N₂和CO₂在沸石ZSM-5上的单组分吸附平衡等温线,温度273～353 K,压力0～500 kPa。采用Sips模型、Toth模型和MSL模型对单组分吸附平衡实验数据进行拟合,拟合结果良好,非线性回归得到相应的模型参数。测量双组分CO₂/N₂、CO₂/CH₄和CH₄/N₂在沸石ZSM-5上的竞争吸附平衡等温线,实验温度为293 K,实验压力为0～500 kPa。采用基于Sips模型的理想吸附溶液理论和双组分MSL模型预测双组分气体在沸石ZSM-5上的竞争吸附平衡等温线,并与实验结果进行比较,预测结果良好。比较CO₂/N₂、CO₂/CH₄以及CH₄/N₂体系在沸石ZSM-5上的竞争吸附选择性系数,探究沸石ZSM-5吸附分离烟道气（CO₂/N₂体系）、垃圾填埋气（CO₂/CH₄体系）或煤层气（CH₄/N₂体系）的可行性,为将来进行工艺设计提供基础数据。     

Infrared study of nitrogen monoxide adsorption on palladium ion-exchanged ZSM-5 catalysts

The adsorption of NO at room temperature on a H-ZSM-5 catalyst exchanged with Pd(NH₃) ₄ ²⁺ complex and activated in oxygen at 773 K has been examined by FTIR spectroscopy. After the oxidizing treatment, the Pd tetrammine complex decomposed into Pd(II) ions and/or Pd(II) hydroxyl complexes dispersed in the zeolite channels. The subsequent adsorption of NO at room temperature led to the reduction of Pd(II) to Pd(I) entities, resulting in the formation and adsorption of NO₂ on H-ZSM-5. The Pd(I) entities were shown to adsorb NO and form mononitrosyl complexes dispersed in the zeolite porosity and characterized by a single infrared absorption band at 1881 cm^–1. The Pd(I) mononitrosyl complex was shown to reversibly coordinate water and NO₂ molecules. The resulting nitrosyl complex was characterized by a single NO vibration band at 1836 cm^–1.     

Intensities of IR stretching bands as a criterion of the strength of Lewis acid sites in ZSM-5 zeolites with bivalent cations

The DFT calculations were applied to investigate the impact of the nature of bivalent cations M (M = Mg²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Mn²⁺, Co²⁺, Ni²⁺) in cation-exchanged ZSM-5 zeolites on the Lewis acid site (LAS) strength. Intensities and shifts of IR stretching bands of adsorbed methane were calculated. Adsorption leads to a decrease in their frequencies and a marked increase in the intensities of the symmetric stretching band of methane. At the same time the intensities of the asymmetric stretching bands decrease. To characterize the strength of LAS, Fukui functions were computed. A good linear correlation between the intensity of methane vibrations and the LAS strengths (Fukui function f ⁺) was found.