Transition metal zeolites

Sierraalta, A., Anez, R. and Brussin, M.-R. (2002) Theoretical study of N02 adsorption on a transition-metal zeolite model, J. Catal., 205, 107. 

Pennline, H. W., Gormley, R. J., and Schehl, R. R. 1984. Process studies with a promoted transition metal-zeolite catalyst. Ind. Eng. Chem. Prod. Res. Dev. 23 388-93. 

The synthesis of phthallocyanines in zeolite Y has been the subject of several publications [52-58]. The different procedures are represented in Scheme 3. In principle, dicyanobenzene is reacted under inert conditions with transition metal zeolites. The latter can be prepared either via ion exchange, or via carbonyl or metallocene impregnation. 

Another characteristic feature of the hydrogen-reduced transition metal zeolites is their acidic properties, as demonstrated by their catalytic behavior (7). Naccache and Ben Taarit (8) gave IR evidence of the subsequent formation of protons on hydrogen-reduced Cu(II)-Y zeolite. Furthermore, transition metal ions have various oxidation states. Owing to the shielding effect caused by the zeolite network and the electric fields, the transition metal ions may be stabilized in unusual oxidation states—i.e. Ni(I) (9). 

The key feature of the adequate transition element seems to be in this ability to stabilize both electrophiles and nucleophiles within the same complex. Extra ligands may or may not increase the reactivity of one of these two species and therefore makethe design of a transition metal zeolite based catalyst within the same ease or difficulty as their homogeneous analogues. 

Unfortunately, the use of TS1 (as well as TS2 discovered in 1990 by the group of Ratnasamy (27)) in catalytic oxidations is restricted to the relatively small substrates able to enter the pores of these zeolites (apertures 0.55 nm). Therefore, many research groups attempted to incorporate titanium in large pore molecular sieves BEA zeolites, mesoporous molecular sieves MCM41 and MCM48. Other transition metal zeolites were also synthesized and tested in oxidation one of the main problems of these systems is the release of redox cations in liquid phase (24). Progress remains to be made to develop molecular sieves catalyzing the oxidation... 

Although industrial application is a major incentive for studying transition metal/zeolite systems, a second motivation is their importance for understanding fundamental principles of heterogeneous catalysis. Two key issues should be mentioned zeolite-imposed stereoselectivity and metal atom reorganization. 

The oxidation of intracrystalline ammonium cations has been reported 3, 65), but most oxidations over zeolites featuring molecular oxygen-hydrocarbon systems have featured transition metal zeolites. The oxidative dehydrogenation of ethylbenzene to styrene and selective oxidation of benzyl alcohol to benzaldehyde over MnY at 250°-370°C were reported earlier 62). Propylene has been oxidized to formaldehyde, COo, and minor quantities or acrolein and acetaldehyde over Cu( II)-exchanged Y-type zeolite (39). 

Fripiat and coworkers have studied a number of transition metal zeolite-catalyzed oxidations recently (50, Si, 52, 53). In the liquid-phase... 

Transition metal oxides, supported catalysts 22-P-08 Transition metal-zeolite models 15-P-13... 

Jiydration reaction. Acetylene is easily hydrated into acetaldehyde over a variety of transition metal zeolites. The metals include zinc, cadmium, copper and silver (27). The evidence for the transition metal involvement comes from an increased reaction rate as the exchange level was increased. It is uncertain whether Y type zeolite would not result in the occurrence of side reaction. The involvement of Bronsted sites seems here less probable in view (i) of the structural type, (ii) of the activity of Ag" " ions and (iii) of the known moderating effect of water on Bronsted acidity at low-to-moderate temperatures. Addition of HX and X2, where X is a halide, is also carried out on cation exchanged zeolites but acidic zeolites are better suited (28). 

Andersen PJ.Bailie JE, Case JL et al (2008) Transition metal/zeolite SCR catalysts. Patent application WO 2008/132452... 

Similar films are obtained from powdered molecular sieves loaded with organic molecules Zeolite Y microparticles embedded into a polystyrene film and loaded with appropriately sized transition metal complexes allow selective electron exchange reactions between trapped and mobile species in the film... 

Compensation-type behavior is quite general and has been extensively studied, especially in transition-metal catalysis [8a], sulfide catalysis [8b], and zeolite catalysis [7]. 

Noble metal catalysts such as Pd, Pt, and Ru and transition metals are deposited on or incorporated in the fibers by methods similar to those used in catalyst preparation. Zeolitic (e.g., TS-M, Na-X, ZSM-type) crystals have been grown on the surfaces. 

Zeolite-like Transition Metal Containing Porous Compounds... 

Partial oxidation reactions are usually carried out over transition metal oxides capable of changing their valent state during their interaction with reacting molecules. Naturally, zeolites with their alumina-silicate composition did not prove themselves as good oxidation catalysts. They failed also to serve as efScient catalyst supporters, since transition metals being introduced into the zeolite matrix lose their ability to activate dioxygen [3,4],... 

Catalysts include oxides, mixed oxides (perovskites) and zeolites [3]. The latter, transition metal ion-exchanged systems, have been shown to exhibit high activities for the decomposition reaction [4-9]. Most studies deal with Fe-zeolites [5-8,10,11], but also Co- and Cu-systems exhibit high activities [4,5]. Especially ZSM-5 catalysts are quite active [3]. Detailed kinetic studies, and those accounting for the influence of other components that may be present, like O2, H2O, NO and SO2, have hardly been reported. For Fe-zeolites mainly a first order in N2O and a zero order in O2 is reported [7,8], although also a positive influence of O2 has been found [11]. Mechanistic studies mainly concern Fe-systems, too [5,7,8,10]. Generally, the reaction can be described by an oxidation of active sites, followed by a removal of the deposited oxygen, either by N2O itself or by recombination, eqs. (2)-(4). 

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