Supercages Of Y-zeolite Research Articles

Selective Oxidation of Thioanisole with Hydrogen Peroxide using Copper Complexes Encapsulated in Zeolite: Formation of a Thermally Stable and Reactive Copper Hydroperoxo Species

[Cu(terpy)]2+ complexes encapsulated into Na-Y zeolite ([Cu(terpy)]2+@Y) were prepared, and their catalytic activities for the oxidation of sulfides using hydrogen peroxide were investigated. Several spectroscopic results, as well as elemental analysis, demonstrated the formation of [Cu(terpy)]2+ complexes in supercages of Y-zeolite. [Cu(terpy)]2+@Y exhibited high selectivity for the oxidation of thioanisole into methylphenylsulfoxide when H2O2 was used. The kinetic study of this oxidation at the catalyst [Cu(terpy)]2+@Y suggests that the reaction of [Cu(terpy)]2+ species with H2O2 is the rate-determining step. The oxidation of thioanisole, benzene, and 2-phenylethylamine using [[Cu(terpy)]2+@Y]*, which was prepared from the reaction between [Cu(terpy)]2+@Y and H2O2, quantitatively proceeded to methylphenylsulfoxide, phenol, and 2-amino-1-phenylethanol, respectively. The reaction of [Cu(terpy)]2+@Y and H2O2 was found to yield thermally stable but active CuII-OOH species in [Cu(terpy)]2+@Y.

Direct oxidation of benzene with molecular oxygen in liquid phase catalysed by heterogeneous copper complexes encapsulated in Y-type zeolite

Liquid-phase direct catalytic oxidation of benzene to phenol was performed by using a copper complex in Faujasite-type zeolite with molecular oxygen as an oxidant and sucrose as a reducing agent. Heterogenisation of the copper complex was achieved by a ship-in-a-bottle method, which enabled the encapsulation of the copper complex in the supercages of a Faujasite-type zeolite. Heterogenisation also provided the catalyst, reactant and the product in separate phases result that allowed their facile separation. All the prepared copper complex-based catalysts exhibited high activity and reusability for the direct oxidation of benzene to phenol. Based on differential thermal analysis, thermogravimetry (DTA-TG) and X-ray absorption fine structure (XAFS) measurements, it was confirmed that the copper complex was encapsulated in the supercages of Y-zeolite. The formation of phenol over the copper complex encapsulated in Y-zeolite was also investigated by using sucrose in the aqueous solution of acetic acid. Sucrose was an effective additive as a reducing agent because it was hydrolysed into two reducing sugars, namely glucose and fructose, under the reaction conditions applied. Overall, this work provides a successful approach for the potential use of heterogeneous metal complex catalysts suitable for liquid-phase oxidation reactions with molecular oxygen.

Template synthesis and characterization of diaza dioxa macrocyclic nanosized cobalt(II) complex dispersed within nanocavity of zeolite-Y

Nanocavity microreactor containing 15- and 16-membered diaza dioxa Schiff-base cobalt(II) complexes “[Co(Et[15]N 2O 2)] 2+, [Co(Pr[16]N 2O 2)] 2+, [Co(Ph[15]N 2O 2)] 2+ and [Co(Ch[15]N 2O 2)] 2+” have been prepared by the template synthesis of diamine (1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene or 1,2-diaminocyclohexane) with [(1,3-bis(2-carboxyaldehydephenoxy)propane)cobalt] 2+;[Co(BCAPP)] 2+@NaY within the pores of zeolite-Y. The nanosized cobalt(II) complex were entrapped in the supercage of Y-zeolite by a three-step process in the liquid phase: (i) exchange of Co(II) ions with NaY in water solution, (ii) reaction of Co(II)–NaY with excess BCAPP in methanol; [Co(BCAPP)] 2+@NaY; (iii) template synthesis of [Co(BCAPP)] 2+@NaY with diamine. The new nanosized complex entrapped in the nanocavity of zeolite Y was characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV–Vis, XRD, BET, DRS, XPS, TGA).

Template synthesis and characterization of hexaaza nickel(II) complex nanoparticles entrapped within the zeolite-Y

Some complexes containing “[Ni([18]py 2N 4)] 2+, [Ni([20]py 2N 4)] 2+, [Ni(Bzo 2[18]py 2N 4)] 2+ and [Ni(Bzo 2[20]py 2N 4)] 2+” were successfully prepared by the template synthesis of 2,6-diacetylpyridine with [bis(diamine)nickel(II)]; [Ni(N–N) 2] 2+; within the zeolite-Y. These complexes were entrapped in the supercage of Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a Ni(II) precursor complex, [Ni(diamine) 2] 2+@NaY, and (ii) template synthesis of the nickel(II) precursor complex with 2,6-diacetylpyridine. The new complex nanoparticles entrapped within the zeolite-Y “[Ni([18]py 2N 4)] 2+@NaY, [Ni([20]py 2N 4)] 2+@NaY, [Ni(Bzo 2[18]py 2N 4)] 2+@NaY, [Ni(Bzo 2[20]py 2N 4)] 2+@NaY” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV–Vis, XRD, BET, DRS). Analysis of the data indicates that the Ni(II) complexes are encapsulated within the zeolite-Y and exhibit different property from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix.

Synthesis, characterization and liquid phase oxidation of cyclohexanol using tert-butylhydroperoxide over host (zeolite-Y)/guest (copper(II) complexes of 12- and 13-membered diaza dioxa Schiff-base macrocyclic ligand) nanocomposite materials (HGNM)

Nanocavity microreactor containing 12- and 13-membered diaza dioxa Schiff-base copper(II) complexes have been prepared by the one-pot template synthesis of (1,8-diamino-3,6-dioxaoctane)copper(II) with bifunctional diketone within the pores of zeolite-Y. The copper(II) complexes were entrapped in the supercage of Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a copper(II) precursor complex, [Cu(1,8-diamino-3,6-dioxaoctane)] 2+-NaY and (ii) template condensation of the copper(II) precursor complex with the bifunctional diketone. Encapsulated copper(II) complex is catalytically very efficient as compared to other neat complexes for oxidation of cyclohexanol with tert-butylhydroperoxide (TBHP) as oxidant and is stable to be recycled without much deterioration.

Nanoscale microreactor-encapsulation of 16-membered hexaaza macrocycle nickel(II) complexes: In situ one-pot template synthesis (IOPTS), characterization and catalytic activity

Nanoscale microreactor containing “1,3,7,9,11,15-hexaazacyclohexadecane “[Ni([16]aneN 6)] 2+” 2, 1,9-dimethyl- “[Ni((Me) 2[16]aneN 6)] 2+” 3; 1,9-diethyl- “[Ni((Et) 2[16]aneN 6)] 2+” 4; 1,9-dibuthyl- “[Ni((Bu) 2[16]aneN 6)] 2+” 5; and 1,9-dibenzyl-1,3,7,9,11,15-hexaazacyclohexadecane “[Ni((Benzyl) 2[16]aneN 6)] 2+” 6”, were successfully prepared by the in situ one-pot template synthesis (IOPTS) of formaldehyde and 1,3-propylenediamine (pn) with alkyl and benzyl amine within the nanodimensional pores of zeolite-Y. These complexes were entrapped in the supercage of Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a Ni(II) precursor complex, [Ni(pn) 2] 2+-NaY 1-NaY, and (ii) IOPTS of the nickel(II) precursor complex with the formaldehyde and amine. The new materials “[Ni([16]aneN 6)] 2+-NaY 2-NaY, [Ni((Me) 2[16]aneN 6)] 2+-NaY 3-NaY, [Ni((Et) 2[16]aneN 6)] 2+-NaY 4-NaY , [Ni((Bu) 2[16]aneN 6)] 2+-NaY 5-NaY, [Ni((Benzyl) 2[16]aneN 6)] 2+-NaY 6-NaY” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV/VIS, XRD, BET, DRS). Analysis of the data indicates that the Ni(II) complexes are encapsulated in the nanodimensional pores of zeolite-Y and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. The host–guest nanoscale hexaaza macrocycle catalyzes the oxidation of cyclohexene with molecular oxygen. Oxidation of cyclohexene with homogeneous catalyst gave 2-cyclohexene-1-one, 2-cyclohexene-2-ol and epoxy cyclohexane whereas, oxidation with heterogeneous catalyst resulted in the formation of 2-cyclohexene-1-one and 2-cyclohexene-1-ol. “[Ni((Benzyl) 2[16]aneN 6)] 2+-NaY shows significantly higher catalytic activity than other catalysts. The effect of temperature, and the amount of 6-NaY used on the catalytic activity and product selectivity were discussed.

Synthesis, characterization and catalytic activity of copper(II) complexes of 14-membered macrocyclic ligand; 3,10-dialkyl-dibenzo-1,3,5,8,10,12-hexaazacyclotetradecanel/zeolite encapsulated nanocomposite materials

Nanodimensional microreactor containing (3,10-dialkyl-dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane)copper(II) complexes have been prepared by the one-pot template synthesis of formaldehyde and 1,2-phenylenediamine (1,2-phen) with alkyl and benzyl amine within the pores of zeolite-Y. The copper(II) complexes were entrapped in the supercage of Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a copper(II) precursor complex, [Cu(1,2-phen) 2] 2+-NaY, and (ii) template condensation of the copper(II) precursor complex with the formaldehyde and amine. The spectra of the neat and encapsulated complexes show that the four secondary nitrogen atoms are coordinated to the copper(II) ion. Encapsulated copper(II) complex is catalytically very efficient as compared to other neat complexes for the partial oxidation of benzyl alcohol with hydrogen peroxide as oxidant and is stable to be recycled without much deterioration.

Synthesis, loading control and preliminary tests of 2,4,6-triphenylpyrylium supported onto Y-zeolite as solar photocatalyst

A heterogeneous photocatalyst has been obtained by hosting the 2,4,6-triphenylpyrylium cation inside the supercages of Y-zeolite. Preparation of the new material has been achieved by means of a formal ion exchange in aqueous medium. Nevertheless, the mechanism is more complex, as bulky 2,4,6-triphenylpyrylium cation is unable to diffuse through the channels of Y-zeolite. The following steps are involved: (a) hydrolytic opening of the pyrylium ion to give a linear diketone; (b) diffusion of the diketone through the channels to reach the supercages; and (c) thermal recyclization under dehydrating conditions. Elemental analysis of the new material was consistent with the pyrylium cation located inside the zeolite. No sulfur was found in the loaded zeolite, indicating that hydrogensulfate is no longer the counter-ion of pyrylium. Accordingly, the stoichiometric amount of Na + was found in the filtered waters recovered after the synthesis. Besides, the IR spectrum of the dry material was coincident with that of 2,4,6-triphenylpyrylium, while the spectrum of a less thoroughly dried sample showed, together with the absorption bands corresponding to pyrylium, other bands assignable to the diketone. Zeolite loading can be controlled in the range of 3–15% of organic carbon. The performance of the new material as a solar photocatalyst for oxidative pollutant degradation was checked using four cinnamic acid derivatives as target compounds. Aqueous solutions (250 mL) of these model pollutants (0.001 M) were irradiated by solar light in the presence of different amounts of solid photocatalyst. Oxidation was efficiently achieved as analysed by HPLC and followed in all cases a pseudo first order kinetics. The most satisfactory results were obtained using 1 g/L of Y-zeolite containing 6% of 2,4,6-triphenylpyrylium cation.

Novel phenomenon of enhancement of IR absorption of CO adsorbed on nanoparticles of Pd confined in supercages of Y-zeolite

Nanoparticles of palladium were synthesized by a `ship-in-a-bottle' technique in supercages of Y-zeolite. The ions of Pd 2+ were introduced into the zeolite by ion-exchange between PdCl 2 and NaY zeolite. They were then reduced by an electrochemical method and assembled to form nanoparticals by admission and release of CO. The electrode of palladium-loading zeolite film was characterized by cyclic voltammetry, and the adsorption of carbon monoxide on the electrode was studied using in situ electrochemical FTIR reflection spectroscopy. A novel phenomenon of enhanced IR absorption (EIRA) was observed for the first time. In comparison with CO adsorbed on a massive Pd electrode, the IR absorption of CO adsorbed on nanoparticles of Pd confined in supercages of Y-zeolite has been enhanced to about 51 times.

Zeolite-Based Organized Molecular Assemblies. Photophysical Characterization and Documentation of Donor Oxidation upon Photosensitized Charge Separation

An organized molecular assembly composed of two ruthenium polypyridine complexes, Ru(bpy)(2)(bpz)(2+) and Ru(bpy)(2)(H(2)O)(2)(2+) (where bpy = 2, 2'-bipyridine and bpz = 2, 2'-bipyrazine), has been prepared in adjacent supercages of Y-zeolite. This material has been characterized by diffuse reflectance, electronic absorption, electronic emission, and resonance Raman (RR) spectroscopy, as well as lifetime measurements. The spectral results confirm the identity of the entrapped complexes and resonance Raman measurements show that the relative concentrations of the two complexes within the zeolite particles are identical. A dramatic decrease in emission intensity observed for the adjacent cage assembly, relative to that observed for an appropriate reference material composed of a mixture of zeolite particles containing the separated complexes, indicates strong interaction between the adjacent complexes which provides an additional nonradiative decay pathway. The excited state lifetime measurements implicate a very short-lived component, dominating the decay curve at early times, which is most reasonably attributed to excited-state electron-transfer quenching of the adjacent cage pair. More importantly, analysis of diffuse reflectance spectra acquired during selective (sensitizer) irradiation of a sample of this material, wherein the remaining cages are filled with a suitable acceptor (MV(2+)), provides direct evidence for oxidation of the Ru(bpy)(2)(H(2)O)(2)(2+) donor complex, confirming the targeted synergy of the adjacent cage assembly.

Zeolite-entrapped organized molecular assemblies. New evidence for highly efficient adjacent cage dyad formation and constrained rotational mobility of tris-ligated polypyridine complexes.

The primary objectives of the present work are to investigate the extent to which an entrapped, tris-ligated polypyridine complex of divalent ruthenium is restricted from rotating within the supercage of Y-zeolite and to provide additional evidence for the high efficiency of synthetic procedures developed for the preparation of adjacent cage dyads entrapped within the Y-zeolite framework. Specifically, the Y-zeolite entrapped complex, Z-[Ru(bpy)(2)(pypz)(2+) ] (where the prefix, Z, indicated a zeolite entrapped complex, bpy = 2,2'-bipyridine and pypz = 2-2-pyridylpyrazine), which contains only one reactive peripheral nitrogen atom, is shown to react with the reagent, (H(2)O)Ru(NH(3))(5)(2+), to yield the entrapped Z-[Ru(bpy)(2)(pypz)-Ru(NH(3))(5)](4+) complex. Treatment with a large excess of bpy, according to previously documented procedures, leads to the formation of the entrapped adjacent cage dyad, Z-[Ru(bpy)(2)(pypz)(2+)/Ru(bpy)(3)(2+)], wherein the two-component complexes are entrapped in adjacent supercages. Spectroscopic measurements confirm the integrity of the component complexes and document a strong interaction between them. Most importantly, it is shown that a second treatment of this material with a large excess of the[(H(2)O)Ru(NH(3))(5)](2+) reagent does not lead to formation of significant amounts of Z-[Ru(bpy)(2)(pypz)-Ru(NH(3))(5)](4+); i.e., the presence of the Ru(bpy)(3)(2+) in the cage adjacent to the primary complex shields the latter from further reaction with the ruthenium pentammine reagent. This result demonstrates that, during the formation of the Ru(bpy)(3)(2+) secondary complex, the detached Ru(NH(3))(5)(2+) fragment does not drift into remote supercages, thereby providing unequivocal evidence for the high efficiency of the synthetic procedure for adjacent cage dyad formation. Furthermore, this result also makes it clear that rotation of the tris-ligated primary complex is restricted by the confinement of the Y-zeolite supercage to the extent that the single reactive peripheral nitrogen cannot be repositioned to a different window of the surrounding supercage.

The development of zeolite-entrapped organized molecular assemblies.

A brief summary is presented of the development of organized molecular assemblies entrapped within the supercages of Y-zeolite. Emphasis is placed on work originating in the author's laboratory, although a discussion of some of the important contributions made by other workers, which inspired and facilitated this work, are included. Following pioneering studies by Lunsford and co-workers, which demonstrated the feasibility of encapsulating the common photosensitizer [Ru(bpy)3]2+ within the Y-zeolite supercage, Dutta and co-workers documented efficient photoinduced electron transfer to viologen acceptors occupying neighboring supercages. We have extended the range of available materials by developing synthetically versatile methods to permit the incorporation of heteroleptic complexes, including constituent ligands which contain peripheral nitrogen donor groups; for example, 2,2'-bipyrazine. In an impressive study employing zeolite-excluded acceptors, Dutta and co-workers showed that the reducing equivalents available from photoinduced electron transfer from the zeolite entrapped sensitizer to intra-zeolite acceptors could be transferred to the extra-zeolite acceptors in aqueous suspensions, although the net charge-separation efficiency was low, presumably because of a persistent relatively efficient back-electron transfer process involving the primary photoproduct; that is, the entrapped sensitizer-acceptor dyad. Exploiting the susceptibility of certain heteroleptic complexes to add reactive ruthenium reagents, methods were developed to construct spatially organized donor-sensitizer-acceptor triads within the supercage framework of Y-zeolite. Such assemblies exhibit dramatically improved net charge-separation efficiencies, presumably as a consequence of inhibiting the wasteful back-electron transfer reaction between the initial sensitizer-acceptor couple.

Synthesis and Spectroscopic Characterization of a Zeolite-Entrapped Ru(bpy)(2)(dpp)(2+) Complex.

The heteroleptic ruthenium(II) complex Ru(bpy)(2)(dpp)(2+) (where bpy = 2,2'-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) has been prepared in the supercages of Y-zeolite and characterized by diffuse reflectance, electronic absorption, electronic emission, and resonance Raman (RR) spectroscopy, as well as lifetime measurements. The spectral results confirm the identity of the entrapped complex. The diffuse reflectance spectrum of the zeolite-entrapped complex is slightly red-shifted in the visible region compared to the absorption spectrum of the free complex in water solution. The emission maximum for the zeolite-entrapped complex is red-shifted by 16 nm with respect to the complex in water solution and by 38 nm relative to the complex in acetonitrile solution. The emission maximum for a zeolite surface-adsorbed complex is blue-shifted by 12 nm with respect to the complex in water solution, but the emission maxima of the liberated complex after dissolution of the zeolite matrix, for both the entrapped and adsorbed complexes, are identical to the spectrum of the free complex in water solution. There are moderate RR frequency shifts observed for the zeolite-entrapped complex relative to the solution-phase complex as a consequence of the interaction of the complex with the zeolite framework. The excited state lifetime measurement shows no dramatic changes upon entrapment within the zeolite supercages. Temperature-dependent lifetime measurements indicate that the excited state decays via two thermally accessible upper states.

Synthesis and Spectroscopic Characterization of Zinc Tetra(3,4-pyridine)Porphyrazine Entrapped within the Supercages of Y-Zeolite.

In this work, the generation of Y-zeolite-entrapped zinc tetra(3,4-pyridine)porphyrazine (ZnPz-Z) at several loading levels is reported. The ZnPz-Z samples were obtained using the template synthesis method involving condensation of 3,4-dicyanopyridine (DCP) around Zn(2+) cations which had been ion-exchanged into the Y-zeolite supercages (Zn(2+)-Z). The integrity of the sample was documented by diffuse reflectance (DR), emission (Em) and resonance Raman (RR) spectroscopic data. The Raman spectrum for the ground-state ZnPz-Z intrazeolitic complex, with the laser excitation at lambda(ex) = 568.2 nm, closely matched that obtained for the free ZnPz porphyrazine, with some bands exhibiting slight frequency shifts of 1-5 cm(-)(1). The DR spectrum of ZnPz-Z exhibited maxima at lambda(max) = 414 and 682 nm, and the emission spectrum of ZnPz-Z revealed fluorescence at lambda(em) = 705 nm, with lambda(ex) = 350.9, 406.7, or 647.1 nm. This emission was 22 nm red shifted with respect to that recorded for the free ZnPz complex in pyridine solution and 24 nm red shifted relative to that acquired for the ZnPz complex adsorbed on the outer surface of the zeolite. All these spectroscopic data suggest that the ZnPz molecules within the zeolite supercages were only slightly distorted. The ZnPz-Z samples contain a small amount of luminescent (lambda(em) = 500 nm) impurities assigned to products of 3,4-dicyanopyridine noncyclic condensation.

Zeolite encapsulated vanadium oxo species for the catalytic reduction of NO by NH 3

Vanadium oxo species have been introduced into the supercages of Y-zeolite by adsorption and decomposition of VOC1 3 to produce catalysts for the study of the effects of oxo vanadium site isolation on catalytic reduction of NO with NH 3. 51V solid-state MAS-NMR of calcined samples with up to 4 V atoms per supercage show that Y-zeolite stabilizes vanadium with octahedral, V 2O 5-like square pyramidal, and most commonly, tetrahedral coordinations. Two distinct isolated tetrahedral environments were identified with NMR resonances around −530 and −830 ppm. There was no NMR evidence for oxygen bridge-bonded vanadia structures in the tetrahedral species in these catalysts. DRIFTS shows that ammonia adsorbs primarily on Bronsted acid sites associated with both the zeolite and the vanadium oxo species. DRIFTS during NO reaction with preadsorbed NH 3 shows the production of a hydroxyl species at 3690 cm −1, which was assigned to V +4-OH, in agreement with the literature. Turnover frequencies, based on NO conversion and total vanadium loading, range from 1 × 10 −5 to 3 × 10 −4 s −1 with selectivity to N 2 of 90–100%. Steady-state reaction experiments indicate that isolated vanadia species are viable sites for the catalytic reduction of NO.

Preparation and catalysis of a copper—pyridine complex encapsulated into a zeolite supercage

A copper (II)-pyridine derivative complex was encapsulated into the supercage of Y-zeolite and characterized using several spectroscopic techniques such as IR, ESR and XANES. The complex was found to be easily reduced to Cu(I) under vacuum at 200°C and re-oxidized to Cu(II) upon exposure to O 2 in its reduced state. In the oxidative coupling of 2,6-dimethylphenol, the catalytically active copper species isolated in the zeolite supercage led to a polymerized compound as the predominant product. When the active species was placed in a hydrophobic environment by treating the supercage with trimethylchlorosilane vapor at 200°C, the catalytic activity was increased by enhancing the re-oxidation step of the copper ion.