Generation of active site confined inside supercage of NaY zeolite on a nano-scale and its ethylene polymerization

To generate an active site that consisted of one Cp₂ZrCl₂ molecule and 1-2 MAO molecules inside supercage of NaY zeolite, two preparation ways for supported catalyst were estimated. First, higher concentration of MAO and Cp₂ZrCl₂, and long reaction time were introduced during the preparation of supported catalyst. It showed activity in ethylene polymerization without any additional MAO. It indicates that Cp₂ZrCl₂ coordinated with only 1-2 MAO molecules could be an active site due to the fact that supercage has nano-scaled diameter of supercage, 1.2 nm, and it could contain only 1-2 MAO molecules inside it theoretically. In situ generation of active site between NaY/MAO and homogeneous Cp₂ZrCl₂ also showed experimental evidence that an active site was generated inside the supercage of NaY zeolite. It showed low activity with long activation time, suggesting the presence of a diffusion effect of Cp₂ZrCl₂ in the pore of NaY. However, NaY/Cp₂ZrCl₂ and homogeneous MAO system showed the characteristic PE polymerization with homogeneous catalyst, indicating that active site was not generated inside the supercage of NaY.     

Synthesis of Flower-like NaY(MoO4)2 and Optical Property of NaY(MoO4)2:Eu3+

Flower-like NaY(MoO₄)₂ particles were synthesized through a microwave-assisted hydrother-mal process followed by a subsequent calcination process. The products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron mi-croscopy. The possible formation mechanism of the flower-like NaY(MoO₄)₂ precursor was proposed. The NaY(MoO₄)₂:Eu³⁺ phosphors were also prepared and their luminescence properties showed the NaY(MoO₄)₂:Eu³⁺ materials with the emission peak at 612 nm had potential application as a red phosphor for white light-emitting diodes. Furthermore, the microwave-assisted hydrothermal process followed by a subsequent calcination process could be extended to prepare the other lanthanide molybdates with the flower-like morphology.     

Shape and diffusion of the monomer‐controlled copolymerization of ethylene and α‐olefins over Cp2ZrCl2 confined in the nanospace of the supercage of NaY

Cp₂ZrCl₂ confined inside the supercage of NaY zeolites [NaY/methylaluminoxane (MAO)/Cp₂ZrCl₂] exhibited the shape and diffusion of a monomer‐controlled copolymerization mechanism that strongly depended on the molecular structure of the monomer and its size. For the ethylene–propylene copolymerization, NaY/MAO/Cp₂ZrCl₂ showed the effect of the comonomer on the increase in the polymerization rate in the presence of propylene, whereas the ethylene/1‐hexene copolymerization showed little comonomer effect, and the ethylene/1‐octene copolymerization instead showed a comonomer depression effect on the polymerization rate. Isobutylene, having a larger kinetic diameter, had little influence on the copolymerization behaviors with NaY/MAO/Cp₂ZrCl₂ for the ethylene–isobutylene copolymerization, which showed evidence of the shape and diffusion of a monomer‐controlled mechanism. The content of the comonomer in the copolymer chain prepared with NaY/MAO/Cp₂ZrCl₂ decreased by about one‐half in comparison with that of Cp₂ZrCl₂. A differential scanning calorimetry study on the melting endotherms after the successive annealing of the copolymers showed that the copolymers of NaY/MAO/Cp₂ZrCl₂ had narrow comonomer distributions, whereas those of homogeneous Cp₂ZrCl₂ were broad. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2171–2179, 2003     

Synthesis of NaX and NaY Zeolites from Tunisian Kaolinite as Base Catalysts: An Investigation of Knoevenagel Condensation

The synthesis of Faujasite‐type zeolites with high purity has been successfully performed from Tunisian kaolinite and the effects of different crystallization parameters on the final products were widely investigated. The alkaline fusion of kaolinite followed by hydrothermal treatment lead to zeolite NaX synthesis whereas the classic hydrothermal transformation of metakaolinite produces NaY zeolite. The results show that an increase in the synthesis temperature and time has improved the crystallization process of the zeolite NaX whereas the SiO₂/Al₂O₃ and the Na₂O/SiO₂ molar ratios were the key parameters to obtain a pure zeolite NaY. The highest specific surface areas obtained with the optimal crystallization conditions were 554 m2 g^?1 and 592 m2 g^?1 for respectively NaX and NaY zeolites. The basic properties of NaX and NaY zeolites were explored in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 140 °C as a test reaction in the absence of solvent. The influence of ion exchange with cesium cation on the catalytic activity of prepared catalysts was also investigated. It was found that the NaX provided higher activity than that of NaY catalyst due to its lower Si/Al ratio whereas a cesium exchange conferred higher basicity to the prepared Na‐faujasite.     

Dehydrogenation activities of highly dispersed transition metal oxides on NaY zeolite

Highly dispersed α-Fe_2O_3/NaY,NiO/NaY,and CuO/NaY catalyst systems were pre-pared by impregnation method.Dispersion thresholds of the transition metal oxides on NaY" zeolitewere determined by XRD phase analysis.The dispersion capacities of the transition metal oxides on NaYzeolite are much lower than that estimated on the basis of a closed packed monolayer in the micropores.The catalytic activity and selectivity of the highly dispersed oxide catalyst systems for ethylben-zene and cyclohexane dehydrogenation reactions were reported.     

Fe(phen)32+‐Modified Zeolite Particles and Their Energetic Studies

Chemically modified zeolite Y (NaY) particles and their resulting modified electrodes were prepared with acridinium (AcH+), iron(II) and 1,10‐phenanthroline (phen) for energetic studies. According to diffuse reflectance absorption spectroscopy and cyclic voltammetry, AcH⁺ and Fe(phen)₃²⁺ were successfully entrapped in the zeolite particles. Transient emission spectra measurements showed that the life time of AcH+* in the zeolite particles (to 35 ns; λ_ex 365 nm; λ_em 500 nm) was greatly reduced upon incorporating Fe(phen)₃²⁺ and Fe²⁺. The fast de cay of AcH+*(NaY) suggested that a reductive quench was likely to take place in the zeolite particle. Probably due to a size‐exclusion effect, the bulky electron donor, N, N‐diethyl‐2‐methyl‐1,4‐phenylenediamine (DEPD), revealed a difficulty in reaching the photosensitizer, AcH⁺, in side the zeolite particle. As a consequence, the in significant photocurrent for the oxidation of DEPD was from the NaY|AcH⁺ electrode. However, if Fe²⁺ and Fe(phen)₃²⁺ were incorporated, the photocurrent would become more significant. Closer examinations, in addition, showed that the photooxidaton of DEPD occurred more rapidly on the NaY|AcH⁺|Fe(phen)₃²⁺ electrode, compared to the NaY|AcH⁺|Fe²⁺ electrode. This difference apparently results from a greater gap in energetics between DEPD and Fe(phen)₃³⁺_(NaY) than that between DEPD and Fe³⁺_(NaY). Due to this effect, a greater amount of indophenol blue, derived from the coupling reaction of the oxidized DEPD with 1‐naphthol, was formed and de posited on the NaY|AcH⁺|Fe(phen)₃²⁺modified electrode. Thanks to this photo‐induced charge‐transfer reaction, the NaY|AcH⁺|Fe(phen)₃²⁺ particle showed an application potential in image recording.     

Template synthesis and characterization of host (nanopores of zeolite Y)/guest (Co(II)-tetraoxodithiatetraaza macrocyclic complexes) nanocomposite materials

A series of Co(II) tetraoxodithiatetraaza macrocyclic complexes ([18]aneN₄S₂, [20]aneN₄S₂, Bzo₂[18]aneN₄S₂ and Bzo₂[20]aneN₄S₂) have been encapsulated in the nanopores of zeolite Y by template condensation reaction. Co(II) complexes with tetraoxodithiatetraaza macrocyclic ligand were entrapped in the nanopores of zeolite Y by a two-steps process in the liquid phase: (i) ion-exchange of [bis(diamine)cobalt(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [Co(N–N)₂]²⁺–NaY; in the nano-cavity of the zeolite, and (ii) in situ template condensation of the cobalt(II) precursor complex with thiodiglycolic acid. The mode of bonding and overall geometry of the complexes and new host/guest nanocomposite materials ([Co([18]aneN₄S₂)]²⁺–NaY, [Co([20]aneN₄S₂)]²⁺–NaY, [Co(Bzo₂[18]aneN₄S₂)]²⁺–NaY, [Co(Bzo₂[20]aneN₄S₂)²⁺–NaY) has been inferred through FT-IR, DRS and UV–Vis spectroscopic techniques, BET technique, molar conductance and magnetic moment data, XRD and elemental analysis, as well as nitrogen adsorption. The average number of encapsulated Co complexes per nano-cavity was determined to be 0.33 for the Co complexes–NaY. An octahedral geometry around the cobalt(II) ion is suggested for the complexes and new host/guest nanocomposite materials.     

以催化裂化废催化剂为原料合成NaY分子筛的研究

针对催化裂化(FCC)废催化剂的回收利用问题,提出了一种废催化剂再利用的方法,即以FCC废催化剂为铝源,合成时只补充部分硅源,采用自制的高效NaY沸石导向剂,水热合成NaY分子筛。同时,以普通的化工原料合成了对比试样Y型分子筛。讨论了不同的FCC废催化剂预处理方式对合成产物性能的影响,发现以经过碱熔活化处理的废催化剂为原料合成的Y分子筛拥有更高的结晶度和纯度。采用X射线衍射、热分析、程序升温脱附法(NH3-TPD)和N₂静态容量吸附法对结晶产物和对比样品的晶体结构,热稳定性、酸性质、比表面积以及孔分布进行了表征。结果显示,以FCC废催化剂为原料完全可以合成出与普通原料性能接近的NaY分子筛。其BET比表面积可以达到615 m²·g^-1,孔体积可达0.38 cm³·g^-1,孔径集中在0.51 nm左右。     

NaY Zeolite Functionalized by Sulfamic Acid/Cu(OAc)2 as a Novel and Reusable Heterogeneous Hybrid Catalyst in Efficient Synthesis of Bis,Tris, and Tetrakis(indolyl)methanes, 3,4‐Dihydropyrimidin‐2(1H)‐ones,and 2‐Aryl‐1H‐benzothiazoles

An efficient acid‐catalyzed synthesis of some bis, tris, and tetrakis(indolyl)methanes, 3,4‐dihydropyrimidin‐2(1H )‐ones, and 2‐aryl‐1H ‐benzothiazoles is reported using NaY zeolite functionalized by sulfamic acid/Cu(OAc )₂ (NaY zeolite‐NHSO₃H /Cu(OAc )₂) in excellent yield. The heterogeneous catalyst has a simple work‐up procedure and could be recycled and reused for six reaction cycles.     

Electron spin resonance spectra observed in the course of grafting iron carbonyls on sodium-Y zeolites

The adsorption and/or decomposition pathway of Fe₂(CO)₉ or Fe₃(CO)₁₂ on hydrated or dehydrated NaY zeolites has been studied by an ESR technique. The adsorption resulted in the formation of three paramagnetic species withg _iso=2.0450, 2.0378, and 2.0016, which were attributable to Fe₃(CO)₁₁ ^–, Fe₂(CO)₈ ^–, and Fe(CO)₄ ^– anion radicals, respectively. These radicals have been suggested as intermediates in the formation of HFe₃(CO)₁₁ ^– on the hydrated NaY zeolite and Fe₃(CO)₁₂ on the dehydrated NaY zeolite.     

Kinetics and catalysis by NaY entrapped Pt carbonyl clusters in the CO+NO reaction

[Pt₁₂(CO)₂₄]^2–/NaY and [Pt₉(CO)₁₈]^2–/NaY exhibited much higher activities in the CO+NO reaction at 473 K compared with Pt/Al₂O₃. Kinetic study andin-situ FTIR results suggest that NO adsorption is the rate-limiting step in the CO+NO reaction on intrazeolite Pt carbonyl clusters.     

Zeolite NaY-mediated oxidation of dyes with H2O2: unique heterogeneous non-transition metal center cleavage of H2O2 under visible light irradiation

This study investigated the visible-light catalysis mediated by zeolite NaY on the oxidation of dyes with H₂O₂. The results demonstrated that zeolite NaY acts as a sink for the electron from the photo-excited dye in the heterogeneous catalysis. Furthermore, the electron can effectively activate H₂O₂ to produce ^·OH radical that is a powerful oxidant for the oxidation of dye at room temperature. The effects of the framework topology, Si/Al ratio, and exchangeable cation of the zeolite on the oxidation of various dyes were also shown.     

Ship-in-a-bottle formation of Ru3(CO)12 in zeolite NaY

A NaY zeolite entrapped Ru₃(CO)₁₂ cluster has been synthesized from RuCl₃ ionexchanged NaY, which are well characterized by IR and Raman spectroscopy and CO chemisorption. When the Ru³⁺/NaY sample is heated from 298 to 393 K for 25 h and kept for 10–20 h at 393 K, the sample color changes from dark to brown-yellow. Thein situ infrared spectrum exhibits bands at 2130, 2064, 2040, 2017, 1990, 1953 and 1925 cm⁻¹. The bands at 2064, 2040, 2017 and 1990 cm⁻¹ are assigned to Ru₃(CO)₁₂/NaY, which are close to crystalline Ru₃(CO)₁₂. Furthermore, Raman results provide the bands at 150 and 185 cm⁻¹, which are attributed to Ru-Ru bonds of crystalline Ru₃(CO)₁₂). CO chemisorption on [Ru₃]/NaY gives a CO/Ru ratio of 3.85, which is similar to the stoichiometry of Ru₃(CO)₁₂ (CO/Ru=4.0).     

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.     

The Adsorption of CHClF2 on NaY5.6 Zeolite

The adsorption of CHClF₂ on NaY5.6 zeolite has been studied by measuring the H and F NMR of the adsorbed CHClF₂, focusing in particular on the measurements of the chemical shift and longitudinal relaxation time, as well as the adsorption isotherm measurements. It is possible to determine the coordination structure of the CHClF₂ adsorbed on NaY5.6 zeolite by measuring the adsorption amount dependence of the chemical shift. In addition, the motional activity of the adsorbed molecules in the super cage of the zeolite is discussed on the basis of observed longitudinal relaxation times for various adsorption amounts.     

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.     

CO Hydrogenation over Re-Co Bimetallic Catalysts Supported over SiO2, Al2O3 and NaY Zeolite

The promotion of rhenium on the reduction of Co²⁺ ions in cobalt based samples prepared by various methods, such as, sol/gel technique, incipient wetness impregnationof Al₂O₃ and NaY, has been investigated in the CO hydrogenation. Among the samples the reducibility of the sol/gel, Re-Co/Al₂O₃ and Re-Co/NaY(IM) were the highest compared to Re-Co/NaY (IE) [8]. In addition to facilitating reduction of Co²⁺ ions, the rhenium increased the rate of reaction and the formation ofC₅₊ hydrocarbons at 10 bar pressures. The samples pretreated in various manner, revealed an about five fold increase in activity and an increase in the chain length in the NaYsupported sample while the activity and selectivity changed in various way in the sol/gel prepared samples. Simultaneously, rhenium increased the amount of olefins of low carbon numbers.In the mechanism the rhenium provides an action preventing fast deactivation of cobalt.     

Photooxygenation and photodimerization of 4-methoxystyrene in NaY. The role of co-adsorbed water and alkene–oxygen charge-transfer complex

On adsorption into NaY, 36% of 4-methoxystyrene (1) was consumed to yield its cis- and trans- chain dimers 2. Irradiation of the NaY sample under vacuum gave cyclic dimers 3, probably through the excimer of 1, and also caused trans-to-cis one-way isomerization of 2. When the NaY sample was irradiated under dry oxygen, 4-methoxybenzaldehyde (4) was given as the major product through photoinduced electron-transfer reaction on excitation of the contact charge-transfer complexes between the guest molecules and O₂. The effects of sodium ion and co-adsorbed water on the photodimerization and photooxygenation is also discussed.     

Zeolite NaY-mediated oxidation of dyes with H2O2: unique heterogeneous non-transition metal center cleavage of H2O2 under visible light irradiation

This study investigated the visible-light catalysis mediated by zeolite NaY on the oxidation of dyes with H2O2. The results demonstrated that zeolite NaY acts as a sink for the electron from the photo-excited dye in the heterogeneous catalysis. Furthermore, the electron can effectively activate H2O2 to produce ·OH radical that is a powerful oxidant for the oxidation of dye at room temperature. The effects of the framework topology, Si/Al ratio, and exchangeable cation of the zeolite on the oxidation of various dyes were also shown.     

CO2 diffusivity in LiY and NaY faujasite systems: a combination of molecular dynamics simulations and quasi-elastic neutron scattering experiments

Quasi-elastic Neutron Scattering combined with Molecular Dynamics simulations have been carried out to gain further insight into the CO₂ dynamics in LiY and NaY Faujasites. In both materials, it was pointed out that the transport diffusivity (D_T) increases with the loading whereas the self diffusivity (D_S) decreases. In addition, it was shown that LiY exhibits a significant slower CO₂ self diffusivity process due to a strong interaction between the Li⁺ cation and the adsorbate molecules at the initial stage of diffusion. This result is consistent with higher simulated activation energy in this cation exchanged faujasite form. By contrast, the transport diffusivity is revealed to be slightly faster in LiY than in NaY.