Zirconium phosphates, catalytic properties

Zirconium phosphates have been extensively investigated as intercalation hosts (531. and the catalytic properties of some pillared zirconium phosphates has been reviewed by Clearfield (541. 

The catalytic properties of metal-zirconium phosphate solid has also been investigated (21, 349). The catalysts were prepared by the ion exchange of zirconium phosphate with copper, nickel, and chromium ions. Cataljdic dehydration of 2-propanol was studied at 160°-350°C, with zirconium phosphate itself giving the highest activity, yielding 97% propylene at 230°-240°C. Introduction of Cu +, Ni +, and Cr " decreased the dehydrating properties, and also decreased the catalytic isomerizing properties when tested with the cyclohexane-methylcyclopentane isomerization. The introduction of copper and nickel improved the dehydration properties of zirconium phosphate when tested on ethylbenzene. 

In heterogeneous catalysts, the tailored and pillared cavity is an essential property as it enables the movement of reactants to inner catalytic sites. The mass transfer of reactants and products inside the pores is mainly influenced by the interaction of the internal walls of the channel with organic molecules, and can consequently be controlled by the difference in polarities. To ensure such properties, anchored ruthenium hybrid zirconium phosphate-phosphonates coated with hydrophobic linear double-stranded polystyrene over the inner surface of the Zr layers were prepared by the first complexation of Ru and then molding of inorganic backbone method, and used as the catalyst in the ATH of o-, m- and p-substituted acetophenones (Fig. 42) [121]. This catalyst showed good catalytic activity and enantioselectivity (73.6-95.6 % ees) in the aqueous reduction with FA-TEA as the hydrogen donor, and could retain its catalytic properties after five runs in the case of acetophenone. 

In the present work the catalytic activity, stracture, plysical and chemical properties of silver-containing zirconium phosphates, containing different amounts of silver, and synthesized using sol-gel, co-precipitation and ion exchange methods have been studied. It was shown that the method of phosphate synthesis determines the final composition, structure and catalytic properties. The phosphates, treated in reducing media, exhibit catalytic activity in the process of ethylene glycol oxidation into glyoxal. 

One of the main tasks in the field of catalysis is a purposeful organization of catalyst structure and stability of active sites. From this point of view, NASICON-type zirconium phosphates mixed with different metals, providing properties such as ionic conductivity, thermal and chemical stability, etc., are of particnlar interest. The ionic conductivity of the phosphates under specific conditions allows forming the active component particles with a given size on the matrix surface, and also providing their stability in the catalytic process. At the same time, the composition and stmcture of materials depend on the synthesis technique. 

Each metal phosphate has different crystal structures depending on the preparation and activation conditions. Acid — base properties and catalytic activities usually vary with the crystal structure. By changing the metals and preparetion conditions, it is possible to obtain wide varieties of catalysts of different acid —base properties, surface areas and, crystalline structure. This flexibility enables metal phosphates to be used in many types of reactions. Selected reactions catalyzed by phosphorous metal oxides are listed in Table 3.40. In this section, the acid —base properties and catalytic activities of aluminum phosphorous oxide, boron phosphorous oxide, zirconium phosphorous oxide, and calcium phosphorous oxide are described. 

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