The Adsorption of CHF3 on NaY5.6 Zeolite and Microdynamic Behaviors in Small Pores

Adsorption of CHF₃ on a NaY5.6 zeolite has been studied by the measurement of H and F NMR of the CHF₃ molecule, focusing in particular on the measurements of a chemical shift and a longitudinal relaxation time, together with the adsorption isotherm measurements. A coordination structure of the adsorbed CHF₃ is determined from the relationship between a chemical shift and an adsorption amount. Relaxation times of H and F were measured at respective two resonance frequencies for various adsorption amounts and temperatures. These relaxation data have been analyzed by use of the thermally activated diffusion model proposed by Torrey. From these analyses, various microdynamic variables such as a mean life time of the trapped state and a mean jump distance in the diffusion were determined as functions of an adsorption amount and temperature.     

Thermochemistry study on H2O/NaY zeolite adsorption system

By using an automatic adiabatic calorimeter the heat capacity measurements in the temperature range of 220—320K for H₂O/NaY zeolite adsorption system with various amounts of adsorbed water have been made. In c_p-T curves obtained, there is no peak for solid-liquid phase transition of the adsorbed water. But for H₂O-NaY zeolite system which consists of a saturated H₂O/NaY adsorption system mixed mechanically with a certain amount of water, there are distinct peaks in their c_p-T curves. The peak in the c_p-T curve disappeared as soon as the mixed water in the latter system was evacuated. The facts mentioned above have been discussed from the point of view of the structure of the adsorbed layer and the pore size of zeolite.     

Density of He adsorbed in micropores at 4.2K

The density of He adsorbed in the cylindrical micropores of zeolites NaY and KL has been determined by He adsorption at 4.2K. He adsorption isotherms were then compared with N₂ adsorption isotherms at 77K. Crystallographic considerations of the micropore volumes gave the density of the He adsorbed layer, which is necessary for assessment of ultramicroporosity of less-crystalline microporous solids, such as activated carbons. The determined density of He adsorbed in the cylindrical micropores of the zeolite was in the range 0.22 to 0.26 gml^–1, greater than that of He adsorbed on a flat surface (0.202 gml^–1). A value for the density of He between 0.20 to 0.22 gml^–1 is recommended for evaluation of ultramicroporosity of a slit-shaped microporous system such as activated carbon.     

CO Adsorption on N2‐Precovered NaY Faujasite: A FTIR Analysis of the Resulting Adsorbed Species

To productively complete the information regarding the reversible adsorption of a gas mixture on the micropores of cationic zeolites, the adsorption of the two gases N₂ and CO on NaY faujasite is taken as a model case study. We analyze herein CO adsorption (77 K) on two distinct N₂‐precovered NaY sets (low and medium). We outline the continuous desorption of N₂ adducts during CO admittance to full N₂ desorption for the highest CO loadings. These features contrast with preceding results obtained for N₂ loading on CO‐precovered NaY. By comparing these results with the sole CO admission and combining both studies regarding the co‐adsorption sets, we demonstrate the influence of the basic strength of the two gases regarding the nature of the surface‐adsorbed species formed. We also propose and discuss a hypothesis regarding the formation of adsorbed mixed species having both N₂ and CO as ligands. These new findings strengthen the statistical response of IR signatures as a helpful proposal for analyzing adsorbed species and their assignments. This survey completes the molecular understanding of gas‐mixture adsorption that lacks experimental data to date.     

Derivative Enthalpies of Adsorption of p-Xylene and m-xylene onto NaY and BaY Zeolites at 150°C: Contribution to the prediction of adsorption selectivity

The derivative enthalpies of adsorption of m-xylene and p-xylene onto the NaY and BaY zeolites were measured at 150°C, then compared with those obtained at 25°C, and finally used to predict the selectivity of adsorption of xylene mixtures. Significant differences were observed as the temperature was elevated: for the NaY zeolite, the adsorbate-adsorbate interactions became prevalent, in contrast with the BaY zeolite, between zeolite and derivative interactions were stronger. The difference between the adsorption derivative enthalpies of the two xylenes displayed an abrupt variation from 2 molec. ^–1 for both zeolites, the filling from which selectivity towards m-xylene for the NaY zeolite and towards p-xylene for the BaY zeolite appeared. The preferentially adsorbed xylene was closely connected with the sense of this difference, which changed with the zeolite.This revised version was published online in November 2005 with corrections to the Cover Date.     

H2O/NaY吸附体系的热化学研究

用精密自动绝热量热计测定了在220-320K范围内, 不同含水量的H2O/NaY吸附体系的热容. 结果表明, 在这些吸附体系的Cp-T曲线上均没有水的固-液相变峰. 这说明即使在饱和吸附的情况下, 水分子仍以单分子层的形态存在于NaY表面上, 它们没有形成聚集态. 此外, 还测定了往饱和吸附的H2O/NaY中再加入不同量水后所组成的H2O/NaY体系的热容. 在这些Cp-T曲线上都出现了明显的相变峰. 所加之水一旦脱出, 则相变峰又消失. 这些水存在于分子筛颗粒之间只与外表面接触. 但仍受分子筛表面的影响. 所以它们的熔化热、熔化温度均比正常水的     

CuNaY分子筛的有效吸附位与其脱硫性能的关联性研究

以液相离子交换法制备了一系列不同Cu负载量的CuNaY分子筛;采用XRD及N₂吸附-脱附表征分子筛的微观结构和织构性质,采用动态吸附法考察其对噻吩模拟油的吸附脱硫性能,结合NH₃-TPD和Py-FTIR方法对CuNaY分子筛的酸量和有效Cu⁺物种进行定量分析,研究了CuNaY分子筛的表面酸性和铜物种形态结构对其吸附脱硫性能的影响机制。结果表明,通过改变铜负载量可有效调控改性Y分子筛的表面酸性以及铜物种化学形态;适量铜物种的引入可以最大限度的形成有效吸附位,从而获得最优吸附脱硫性能,而过量的Cu物种会在Y分子筛笼内形成多核铜物种结构,导致有效吸附位点的减少,影响其对噻吩的吸附能力。     

苯并噻吩在酸改性NaY分子筛上的吸附

以NaY分子筛为母体,通过柠檬酸、磷酸改性分别得到吸附剂NaY-C和NaY-P.采用SEM、XRD、XRF、N₂物理吸附及NH₃-TPD表征可知,柠檬酸改性后得到的NaY-C吸附剂介孔表面积增加,分子筛骨架结构保持不变.同时,磷酸改性使得NaY分子筛表面弱酸量减少强酸量增加,改性后所得吸附剂NaY-P的强酸量大于NaY-C.吸附实验表明,NaY-C和NaY-P均可完全脱除模拟油品中的苯并噻吩,同时NaY-C吸附剂对0^#柴油的脱硫能力优于NaY-P吸附剂.再生实验中NaY-C和NaY-P吸附剂对模拟油品的脱硫率由第一次的100%分别下降至第6次的91.97%和85.96%.由此可知,柠檬酸改性NaY分子筛所得NaY-C吸附剂的脱硫能力优于NaY-P,原因是吸附剂上的介孔更易于发生吸附脱硫.     

Adsorption of CO2 and N2 on synthesized NaY zeolite at high temperatures

NaY zeolite particles with a high surface area of 723 m²/g were synthesized by a hydrothermal method. Adsorption isotherms of pure gases CO₂ and N₂ on the synthesized NaY particles were measured at temperatures 303, 323, 348, 373, 398, 423, 448 and 473 K and pressures up to 100 kPa. It was found that the adsorption isotherm of CO₂ on the synthesized zeolite is higher than that on other porous media reported in the literature. All measured adsorption isotherms of CO₂ and N₂ were fitted to adsorption models Sips, Toth, and UNILAN in the measured temperature/pressure range and Henry’s law adsorption equilibrium constants were obtained for all three adsorption models. The adsorption isotherms measured in this work suggest that the NaY zeolite may be capable of capturing CO₂ from flue gas at high temperatures. In addition, isosteric heats of adsorption were calculated from these adsorption isotherms. It was found that temperature has little effect on N₂ adsorption, while it presents marked decrease for CO₂ with an increase of adsorbate loading, which suggests heterogeneous interactions between CO₂ and the zeolite cavity.     

Characterization of CuY zeolites after dehydration,oxidation and reduction with carbon monoxide An adsorption and 129Xe nuclear magnetic resonance spectroscopy study

The adsorption isotherms and ¹²⁹Xe nuclear magnetic resonance (NMR) chemical shifts of xenon and the adsorption isotherms of carbon monoxide of Cu(II)- and Cu(I)-exchanged zeolites NaY were measured. The former zeolites of 53, 75, and 95% exchange degrees were investigated after various pretreatment steps comprising dehydration, oxidation and reduction with CO at 420°C as well as long-term CO reduction at 470°C. The Cu(I)Y zeolite of 70% exchange degree was prepared via a solid-state exchange procedure with CuCl and subjected to dehydration at 420°C. In all cases, except the dehydrated zeolites, almost linear xenon adsorption isotherms and linear ¹²⁹Xe NMR chemical shift _versus xenon concentration curves running parallel to each other are obtained. In contrast, the chemical shift curves for the dehydrated zeolites are non-linear at low xenon concentrations turning towards negative chemical shift values at very low pressures. The whole body of the experimental xenon data can be explained quantitatively with a unifying approach on the basis of a site adsorption model where the sites are (i) two types of cuprous ions of much different adsorption strength and ¹²⁹Xe chemical shift, (ii) Na⁺ cations, (iii) Lewis acid sites generated through autoreduction and reduction of Cu²⁺ by CO, and (iv) framework sites free of cations. These five types of sites are each characterized by Langmuir adsorption isotherm constants and local ¹²⁹Xe NMR chemical shifts. The adsorption site concentrations in the various zeolites are evaluated. The supercage Cu(I) concentration values are in nice agreement with the results deduced from the CO adsorption isotherm measurements.     

Effects of toluene on thiophene adsorption over NaY and Ce(IV)Y zeolites

Zeolites NaY and Ce(IV)Y were employed as adsorbents to remove organic sulfur compounds from model gasoline(MG) solutions with and without toluene in static adsorption experiments at room temperature(RT) and atmospheric pressure.The adsorbents were characterized by XRD,XRF and pyridine infrared spectrum(IR).The adsorption experiments show that the desulfurization performance of Ce(IV)Y is much better than that of NaY.The sulfur removal over both NaY and Ce(IV)Y decreases with the increase of toluene concentration in MG,however,the decline tendency on Ce(IV)Y is smooth,and it is steep on NaY.FT-IR spectra of thiophene adsorption indicate that thiophene molecules are mainly adsorbed on NaY via π electron interaction,but on Ce(IV)Y,in addition to the π electron interaction,both Ce4+-S direct interaction and protonation of thiophene also play important roles.Toluene molecules are adsorbed on NaY also via π electron interaction.Although the amount of Brnsted acid sites is increased due to the introduction of Ce4+ ions into NaY zeolite,it is not found to influence the adsorption mode of toluene over Ce(IV)Y.Compared with NaY zeolite,the improved desulfurization performance over Ce(IV)Y for removing organic sulfur compounds from MG solution,especially those containing large amount of aromatics,may be ascribed to the direct Ce(IV)-S interaction,which is much resistant to the influence resulted from toluene adsorption.     

Determination of Absolute Gas Adsorption Isotherms by Combined Calorimetric and Dielectric Measurements

A new method to determine absolute masses of gas adsorbed on the external and internal surfaces of a porous solid is proposed. It consists on a combination of calorimetric and dielectric measurements. These lead to the enthalpy and the dielectric polarization of the adsorbed phase from which by purely thermodynamic calculations the absolute mass adsorbed can be determined without using the so-called helium volume hypothesis nor any other equivalent assumption.As example adsorption of subcritical carbon dioxide (CO₂) on zeolite (Degussa DAY) at 298 K and pressures up to 0,4 MPa is considered. As expected data of absolute masses adsorbed are always somewhat larger than the corresponding Gibbs excess masses calculated from both volumetric and gravimetric measurements via the helium volume of the zeolite.     

H2分子在LaFeO3表面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,通过计算表面能确定La Fe O_3(010)表面为最稳定的吸附表面,研究了H_2分子在La Fe O_3(010)表面的吸附性质。La Fe O_3(010)表面存在La O和Fe O_2两种终止表面,但吸附主要发生在Fe O_2终止表面,由于La Fe O_3(010)表面弛豫的影响,使得凹凸不平的表面层增加了表面原子与H原子的接触面积,表面晶胞的纵向体积增加约2.5%,有利于H原子向晶体内扩散。研究发现,H_2分子在La Fe O_3(010)表面主要存在3种化学吸附方式:第一种吸附发生在O-O桥位,2个H原子分别吸附在2个O原子上,形成2个-OH基,这是最佳吸附位置,此时H原子与表面O原子的作用主要是H1s与O_2p轨道杂化作用的结果,H-O之间为典型的共价键。H_2分子的解离能垒为1.542 e V,说明表面需要一定的热条件,H_2分子才会发生解离吸附;第二种吸附发生在Fe-O桥位,1个H原子吸附在O原子上形成1个-OH基,另一个H原子吸附在Fe原子上形成金属键;第三种吸附发生在O顶位,2个H原子吸附在同一个O原子上,形成H_2O分子,此时H_2O分子与表面形成物理吸附,H_2O分子逃离表面后容易形成氧空位。此外,H_2分子在La Fe O_3(010)表面还可以发生物理吸附。     

Cd-113 and Al-27 NMR relaxation study of aquoeus solutions adsorbed on silica gels and zeolite NaY

Cd-113 and Al-27 NMR parameters were used to investigate the Cd²⁺ and Al³⁺ hexaaquo metal ions adsorbed on some silica gels and zeolite NaY. No significant variations of the chemical shifts of cadmium and aluminum signals were observed for the aquated ions onto the pores with respect to those of the bulk solutions, thus indicating the absence of oservable specific interactions with the surface. On the contrary an increasing broadness of the signals as the pore size decreased as well as dramatic shortenings of Cd-113 and Al-27 NMR spin-lattice relaxation times were obtained. These variations were mainly ascribed to a reduced mobility of the aquo ions inside the pores. From the comparative analysis of Cd-113 and Al-27 relaxation data the correlation times of Cd(H₂O)₆²⁺ and Al(H₂O)₆³⁺ adsorbed species were estimated together with the quadrupolar coupling constants for Al(H₂O)₆³⁺.     

化学液相沉积法调变沸石孔径及异构体择形分离

本文用化学液相沉积方法精细调变NaY沸石孔径, 在适当的溶剂中硅酯与沸石吸附水或表面羟基作用而沉积于沸石外表面, 沸石孔口有效地被缩小。制备了一系列氧化硅沉积量不同的SiNaY沸石, 红外光谱、比表面和孔体积测量结果表明随着沉积量增加沸石孔径逐渐缩小, 但沸石骨架结构、孔容和内表面性质基本不变。测定了SiNaY样品对于对二甲苯/1, 3, 5-三甲苯, β-甲基萘/α-甲基萘, 1, 2, 4-三甲苯/1, 3, 5-三甲苯, 对二甲苯/间二甲苯和对甲酚/间甲酚五类分子尺寸不同的液体混合体系的择形吸附行为, 发现SiNaY沸石对分子尺寸与沸石孔径相近的混合体系具有良好的择形选择吸附分离性能。     

H2分子在LaFeO3表面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,通过计算表面能确定LaFeO₃(010)表面为最稳定的吸附表面,研究了H₂分子在LaFeO₃(010)表面的吸附性质。LaFeO₃(010)表面存在LaO和FeO₂两种终止表面,但吸附主要发生在FeO₂终止表面,由于LaFeO₃(010)表面弛豫的影响,使得凹凸不平的表面层增加了表面原子与H原子的接触面积,表面晶胞的纵向体积增加约2.5%,有利于H原子向晶体内扩散。研究发现,H₂分子在LaFeO₃(010)表面主要存在3种化学吸附方式:第一种吸附发生在O-O桥位,2个H原子分别吸附在2个O原子上,形成2个-OH基,这是最佳吸附位置,此时H原子与表面O原子的作用主要是H1s与O2p轨道杂化作用的结果,H-O之间为典型的共价键。H₂分子的解离能垒为1.542 eV,说明表面需要一定的热条件,H₂分子才会发生解离吸附;第二种吸附发生在Fe-O桥位,1个H原子吸附在O原子上形成1个-OH基,另一个H原子吸附在Fe原子上形成金属键;第三种吸附发生在O顶位,2个H原子吸附在同一个O原子上,形成H₂O分子,此时H₂O分子与表面形成物理吸附,H₂O分子逃离表面后容易形成氧空位。此外,H₂分子在LaFeO₃(010)表面还可以发生物理吸附。     

Zeolites modified by CuCl for separating CO from gas mixtures containing CO2

Although zeolites such as NaY and 13X adsorb CO₂ much more than CO, the adsorption amount of CO₂ and CO can be reversed if the zeolites are modified with CuCl. When zeolite NaY or 13X is mixed with CuCl and heated, high CO adsorption selectivity and capacity can be obtained. Isotherms show the adsorbents have CO capacity much higher than CO₂. This is because CuCl has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuCl can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO₂ adsorption. The monolayer dispersion of CuCl is confirmed by XRD and EXAFS studies. The loading of CuCl on the zeolites has a threshold below which the CuCl forms monolayer after heating and crystalline phase of CuCl can not be detected by XRD. An adsorbent of CuCl/NaY with CuCl content closed to the monolayer capacity shows very high CO selective adsorbability for CO₂, N₂, H₂ and CH₄. At temperature higher than room temperature, the adsorbent has even better CO selectivity for CO₂. Using the adsorbent, a single-stage 4 beds PSA process, working at 70°C and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%.     

Adsorption equilibria of CO/H2 with a magnetic suspension balance: Purely gravimetric measurement

Adsorption equilibria of pure gases and binary gas mixtures can be measured with a new magnetic suspension balance. For this measurement no additional concentration measurement is required, neither for the gas phase nor for the adsorbed phase. The new instrument allows gravimetric adsorption measurements in a wide range of pressure (UHV...50 MPa) and temperature (210 K...570 K) to be performed. The experimental procedure and the instrument set up is fairly easy and can be compared to pure gas adsorption experiments. The new instrument and experimental procedure have been tested by performing coadsorption measurements with CO/H₂ mixtures on a commercial 5A zeolite.This revised version was published online in November 2005 with corrections to the Cover Date.     

Preparation and catalytic properties of a bimetallic Sn?Pt complex in the supercages of NaY zeolite by use of surface organometallic chemistry

The grafting reaction of SnMe₄ on the surface of Pt/NaY zeolite was investigated in a 1.6 × 10⁴ Pa hydrogen atmosphere. The chemical compositions, structure and properties of the resulting solid were characterized by in situ FTIR, ICP, XRD, XPS, temperature programmed decomposition and nitrogen adsorption. The results show that Pt atoms of Pt/NaY zeolite react with tetramethyltin to form a bimetallic Me₃Sn? Pt surface species in the presence of hydrogen at 353 K. The reaction does not destroy the zeolite framework, while its surface properties are changed. The BET surface area and the pore volume of the zeolite decrease significantly. The CO chemisorption results and the XPS results show that the electronic properties of the modified Pt atoms on the surface of NaY zeolite are altered remarkably by the inductive effect of electron between Pt and methyl groups. The grafted product has excellent selective hydrogenation of furfural to furfuryl alcohol. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermodynamics of Carbon Dioxide Adsorption on the Protonic Zeolite H‐ZSM‐5

Adsorption of carbon dioxide on H‐ZSM‐5 zeolite (Si:Al=11.5:1) was studied by means of variable‐temperature FT‐IR spectroscopy, in the temperature range of 310–365 K. The adsorbed CO₂ molecules interact with the zeolite Brønsted‐acid OH groups bringing about a characteristic red‐shift of the O? H stretching band from 3610 cm^?1 to 3480 cm^?1. Simultaneously, the ν₃ mode of adsorbed CO₂ is observed at 2345 cm^?1. From the variation of integrated intensity of the IR absorption bands at both 3610 and 2345 cm^?1, upon changing temperature (and CO₂ equilibrium pressure), the standard adsorption enthalpy of CO₂ on H‐ZSM‐5 is ΔH⁰=?31.2(±1) kJ mol^?1 and the corresponding entropy change is ΔS⁰=?140(±10) J mol^?1 K^?1. These results are discussed in the context of available data for carbon dioxide adsorption on other protonic, and also alkali‐metal exchanged, zeolites.