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Black plate (277,1) is concluded that a higher activity is conferred by the presence of only straight microporous channels which either contain a greater number of catalytic centres or they are more accessible in the higher zeolite, whereas ZSM-5 contains both straight and sinusoidal channels200. A catalytic application for the elimination of a pollutant is the oxidation of 1,2-dichlorobenzene over various protonic zeolites (H- FAU, H-BEA, H-MFI, H-MCM-22 and ITQ2) and their corre- sponding Pt-loaded equivalents. The process is found to be effective at 350–400C, and while the presence of platinum enhances the activity of the catalyst, it largely increases the yield of by-products such as 1,2,4-trichlorobenzene201. It is also reported that ammonium cations can be removed as a contaminant from aqueous solutions using a Romanian natural volcanic tuff even in the presence of Zn2 þ and Cd2 þ which appear not to decrease the ammonium adsorption capacity of the material202. Broadly in relation to the running of the Metsamor nuclear power plant (NPP) in Armenia, is one paper reporting on the adsorption of tritiated water by Armenian natural zeolites203, and another reporting on the modification of the sorptive properties of natural Armenian zeolites by exposure to radiation from an electron accelerator204. A bactericidal activity has been reported for a silver-exchanged zeolite and which is found to be of the same order as silver nitrate solution. It is proposed that the contact of the bacterial cell with the zeolite causes the transfer of Agþ cations into the cell and that reactive oxygen species which are involved in the mode of bactericidal action of the Ag-zeolite are then generated in situ205. Hemostatic dressings for wounds in battle situations which are based on zeolites (e.g. QuikClot) have been reported. However, the effectiveness of these new dressings on wounds actually sustained in combat is still questionable according to studies and anecdotal reports from Operation Iraqi Freedom. It is concluded that more research is needed to draw definite conclusions about the effectiveness of these materials in a combat setting206. Doubtless there will be no lack of such future opportunities as humans clamour for what remains of the earth’s bestowal of energy sources, metals and water. As this review aims to show, zeolites are remarkable materials with a great variety of practical uses. I call attention to the the Cuban designation1 ‘‘La Roca Magica’’ which accolades them superlatively. I recall that synonyms in Spanish for ‘‘Magica’’ (the adjective form of ‘‘Magico’’) include ‘‘Estupenda’’ and ‘‘Maravillosa’’, and both would seem to suit. www.scienceprogress.co.uk Properties and applications of zeolites 277PDF Image | Properties and applications of zeolites
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