Impregnated zeolites

Molybdenum/zeolite catalysts prepared by impregnating zeolites with ammonium hepiamolybdate solution generally give rise to poor dispersion of molybdenum [2]. In contrast, ion exchange would be an ideal method for loading active metal species onto supports. Few cationic forms are available as simple salts of molybdenum of high oxidation... 

Considering all we know up to now, the specific properties of zeolites can be summarized as follows. Zeolites are aluminosilicates with defined microporous channels or cages. They have excellent ion-exchange properties and can thus be used as water softeners and to remove heavy metal cations from solutions. Furthermore, zeolites have molecular sieve properties, making them very useful for gas separation and adsorption processes, e.g., they can be used as desiccants or for separation of product gas streams in chemical processes. Protonated zeolites are efficient solid-state acids, which are used in catalysis and metal-impregnated zeolites are useful catalysts as well. 

A further possibility for side-chain alkylation of toluene is oxidative methylation with methane. Catalysts with occluded alkali metal oxides, prepared by impregnating zeolites with alkali metal hydroxides followed by calcination, usually exhibit better performance.441 Further enhancement was achieved by impregnating ion-exchanged zeolites 442 Significant improvements in stability and the yields of Cg hydrocarbons were also observed when NaX was impregnated with 13% MgO which was found to increase the amounts of active sites.443... 

Another approach to isolating redox metal ions in stable inorganic matrices, thereby creating oxidation catalysts with unique activity/selectivity relationships, is to incorporate them in a zeolite lattice framework. This is fundamentally different to the metal ion exchanged (i.e. impregnated) zeolites described earlier and the ship in the bottle type zeolites61,62 where a metal... 

The incorporation of rhenium into zeolites via [ReOz(en)2]Cl has been found to lead to lower catalytic activity (in the hydrogenation of benzene) than is the case for catalysts obtained by impregnating zeolite NaY with NH4Re04 solution.388... 

The off-gas passes scrubber containing NaOH solution and filters with silver-impregnated zeolite or charcoal in which Ru and I are retained. Kr may be separated by condensation or adsorption on charcoal at liquid-nitrogen temperature. 

In the above-mentioned studies, solid-state ion exchange was used to prepare the non-acidic catalysts. The coordination of the copper after the preparation did not receive attention. We have prepared non-acidic copper-zeolites by impregnating zeolites of the mordenite type with aqueous copper salts. The preparation and characterization of these materials and the catalytic properties in the chlorobenzene conversion with water and ammonia will be discussed here. A second objective of the present study is to investigate the possibilities of copper-zeolites in nucleophilic substitutions with other chloroaromatics than chlorobenzene as substrates. Therefore, the substitutions of chlorotoluenes and dichlorobenzenes will be tested as model reactions. 

It is likely that the acidity of copper-exchanged zeolites plays a role in this isomerization. However, in initial experiments with copper-impregnated zeolites some isomerization was also detected. Thus the hydrogen chloride evolved during the substitution may also play a role. 

PNNL Copper-impregnated zeolites Y substrate Unnamed 0.8 4.1 2,416,800... 

Intensive research is currently being carried out to obtain efficient catalysts for this reaction. Most of the research is devoted to different metal (Pt, in particular)-based materials, but several approaches include porous materials such as Ni-impregnated zeolites, obtained from soaking of zeolites in, for instance, NiSO4 solutions (Abdel Rahim et al., 2006). The performance of gold-zeolite-modified electrodes toward electrocatalytic oxidation of ethanol, an alternative to methanol fuel, has been recently reported by Ouf et al. (2008). 

When using exchanged and impregnated zeolites, the increase of selectivity was not important. It seemed that the reaction occurred mainly at the external surface of the catalyst meaning for example that the pore size of the modified zeolites was too small. It was one of the reasons for which the preparation of basic mesoporous materials was studied specially the exchange or the impregnation of basic elements. 

In contrast, the hydrodealkylation and hydrocracking became pronounced on all Mo impregnated zeolites (Table 1). For example, benzene became the only aromatic product after 2 hours of reaction on Mo impregnated ZSM-5. 

An approach toward the (asymmetric) aziridination of double bonds was published by ICI [61]. The company disclosed an acidic, copper-impregnated zeolitic material having a pore size large enough for the reactants to enter and for the aziridination product to leave the zeolite supercage. Asymmetric azirid-inations may be conducted by treating the catalyst with a chiral modifier, e.g., the 4,4 -disubstituted bis(oxazoline) 12, before contact with the nitrene donor (PhI=NTs). The aziridines could be isolated in moderate optical purity (30-40% ee)y and Scheme 8 shows the exemplified transformation of styrene (10) to the corresponding aziridine 11. Further details of this topic can be found in a research project, financially supported by Synetix [62]. 

Although GEMS is a more difficult technique experimentally than normal Mdssbauer spectroscopy it offers many exciting possibilities for the study of Mdssbauer isotopes on or near the surface. It could be a useful technique to study the properties of bifunctional zeolite catalysts and metal-impregnated zeolite catalysts. 

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