Zeolite-hosted oxides

Preparation of zeolite-hosted oxides can be carried out either (i) by chemical vapor deposition (C VD), i.e., loading the zeohte with volatile chlorides like TiCl4, VOCI3 or SnCl4 in a nitrogen carrier stream, foUowed by hydrolysis and calcination, or (ii) by impr nation with suitable compoimds such as SnCl4 or VO(acac)2 in aqueous or organic solution and subsequent calcination. 

XRD patterns of the prepared samples V-Mo-Zeolite are similar to that of zeolites which suggests that the metal species (i.e. oxide, cations,...) are well dispersed through the zeolites structure and the absence of bulk phases in the XRD patterns implies that for these samples the molybdenum and vanadium oxides are present in either a nanocrystalline state or as a small crystallites which measured less than 4 nm in diameter. Furthermore, XRD and FTIR (1500-400 cm 1) showed no significant damage of the zeolite host structure after exchange and thermal treatment except for the sample V2MoMor. 

Ship-in-Bottle Synthesis of Sterically Crowded Fe-Phthalocyanines in NaY Zeolite Hosts and Their Catalytic Behavior in Regioselective Oxidation of Alkanes... 

Recently, Ramamurthy and colleagues demonstrated that certain zeolites, including Na-ZSM-5, spontaneously oxidize a variety of olefmic or aromatic substrates (Fig. 1) [34, 35], Zeolites have been utilized frequently as supporting matrix materials [36-38], These materials contain host cavities of well defined geometries and allow molecules of appropriate shapes to be incorporated. Typically, the host contained in the zeolite is oxidized by exposure to ionizing radiation (vide infra), and the resulting radical cation is protected against ion... 

Over the last several years, considerable research has been done on using zeolite hosts for examining oxidation reactions of hydrocarbons, using O2 as the oxidant. 

Alternative oxidants such as potassium iodate were also explored for the intrazeolite polymerization of aniline in NaY and acidic forms of Y zeolite. With peroxydisulfate, the polymerization proceeded only if a sufficient supply of intrazeolite protons was available. No polymer formed in either NaY or in acid zeolites with neutral iodate solution, but at low pH polyaniline was obtained in all hosts. The open nature of the zeolite host, even when partially filled with polymer, permits the introduction of base (such as ammonia). On admission of ammonia into the emeraldine salt-containing zeolite, the protonated polymer was converted into the neutral emeraldine base form. 

The chemical composition of the zeolitic host also affects the basic properties. When the basicity of Cs-over-exchanged zeolites X and Y, with Si/Al ratios of 1.2 and 2.5, respectively, were measured by stepwise thermal desorption of CO, it was found that different cesium oxide species are present CS2O inside the CsNaX zeolite and (Cs20)2 inside the CsNaY zeolite [73,74]. The basicity of the occluded CS2O species was, moreover, greater than that of intrazeolitic clusters (Cs20)2, as deduced from catalytic activity and TPD results. 

The use of zeolite-hosted semiconductor oxides as chemicai sensors towards oxidizing or reducing gases might be attractive. Since the alteration of the conductivity depends on changes of the oxide stoichiometry [93,94], shorter diffusion distances in smaller clusters should result in shorter response times of the sensors. Fast response is a prerequisite for the application of sensors based on changes of the bulk composition, e.g. in air/fuel ratio control devices. 

Alkali and alkaline-earth exchanged zeolites or zeotypes (c.g. MCM-41) [15, 39, 130, 141-155] have been extensively used as base catalysts. However, they are w eak bases. Alternatively, either alkali metal or alkali and alkaline-metal oxides can be occluded into zeolites and zeotypes in order to increase their basicity [18,63, 154, 156-161]. This is usually referred to as the introduction of a basic guest into a zeolite host. Moreover, the loading of Yterbium or Europium metal on zeolites, thus yielding strong bases, has been reported [17]. 

A new method, viz. the recrystallization of MCM-41 impregnated metal complex in the synthesis system of zeolite Y, has been developed to immobilize the guest complex in zeolite host. In this way, a series of FeL/Y composites (with L=phenanthroline (phen), 8-quinolinol (Qx), salicylic acid (SA)) have been prepared. The as-prepared materials are characterized by XRD, FTIR, UV-vis, TG-DTA and ICP techniques. Furthermore, their catalytic properties in the reaction of cyclohexane oxidation were also investigated. It was shown that this method made it possible to immobilize different metal complexes, including the cationic, the anionic and the neutral. In addition, the content of metal complex can be controlled by varying its amount impregnated on MCM-41,... 

Composites containing different types of guests (metal or alloy particles, oxides, sulfides, complexes, polymers) in the cavities of zeolite hosts are prepared for various appHcations in materials research and catalysis. Except for quality assessment by detection of extra-zeolite material after synthesis or thermal treatments, photoemission plays a largely auxiliary role in this area, cooperating with bulk techniques such as X-ray absorption, UV-Vis, IR of probe molecules, and temperature-programmed reduction. The attention drawn to the significance of intra-zeolite potentials by XPS studies [12] has, however, contributed to the elaboration of a new theory of metal-support interactions [18,19]. 

ABSTRACT.The catalytic properties of zeolite framework elements and those of zeolite hosted cations, complexes or oxide particles are reviewed. 

We will focus naturally on the catalytic properties of cation exchanged zeolites then on the catalytic properties of zeolite hosted complexes and small oxide particles. Finally we will attempt to analyze the potential of structural T elements in catalysis in the light of the latest developments of TS-1 catalysis mostly related to organic synthesis. 

The location of the polymer phase is further illustrated by the polymerization rates in the zeolite hosts which are orders of magnitude slower than in bulk chemical solution syntheses (no reaction in A, MOR < Y solution). The oxidant and/or the monomers have to diffuse into the channels of the zeolites in order to reach the intrazeolite reaction partners. These diffusion and pore volume limitations would not have been observed if the polymers had only formed on the crystal surfaces. 

The photooxidation of Mo(CO)6 guest served for the production of intrazeolite Mo(IV) and Mo(VI) oxides [220]. Similarly, the photooxidation of W(CO)6 encapsulated in faujasite zeolites was used for the preparation of non-stoichiometric tungsten oxides WOs- , which can be further readily oxidized or reduced [220a,b]. It has been shown by use of EXAFS that W(CO)6 maintains its molecular integrity at room temperature in a zeolite host, but that photooxidation with molecular oxygen and theimal decomposition at 300-400 °C results in the formation of various intrazeolite tungsten oxides [221, 222]. 

Ferrocene has also been incorporated in zeolite hosts [244, 255] and hydrocarbon loss on heating and oxidation to ferricinium cation were observed. Similarly, substituted ruthenocenes were also investigated [256, 257]. The ring opening polymerization of a [l]silaferrocenophane within the channels of mesoporous silica (MCM-41) gave precursors of magnetic iron nanostructures [257a,b]. 

A 1 1 molar mixture of monomers 2-(3-thienyl)ethyl hexanoate and 2-(3-thienyl)ethanol can be polymerized by chemical oxidation with FeCU and gives a soluble ester-functionaUzed PAT with an electrical conductivity in the doped state of 4.9 X 10 S cm [583,584]. Thiophene, 3-methylthiophene, bithiophene and terthiophene are polymerized in the channels of molecular sieve zeolite hosts. Conducting polymers can be isolated after dissolution of the zeolite host in HF [615]. 

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