Zirconium phosphates, catalytic

Both aluminum oxide and zirconium oxide are catalytically interesting materials. Pure zirconium oxide is a weak acid catalyst and to increase its acid strength and thermal stability it is usually modified with anions such as phosphates. In the context of mesoporous zirconia prepared from zirconium sulfate using the S+X I+ synthesis route it was found that by ion exchanging sulfate counter-anions in the product with phosphates, thermally stable microporous zirconium oxo-phosphates could be obtained [30-32]. Thermally stable mesoporous zirconium phosphate, zirconium oxo-phosphate and sulfate were synthesized in a similar way [33, 34], The often-encountered thermal instability of transition metal oxide mesoporous materials was circumvented in these studies by delayed crystallization caused by the presence of phosphate or sulfate anions. 

Enones are reduced to saturated ketones by catalytic hydrogenation provided the reaction is stopped following the absorption of 1 mol of hydrogen. " A number of catalysts were found useful for this, including platinum, platinum oxide,Pt/C, " Pd/C, - Rh/C, " tris(triphenylphosphine)rhodium chloride, - nickel-aluminum alloy in 10% aqueous NaOH, and zinc-reduced nickel in an aqueous medium. Mesityl oxide is formed from acetone and reduced in a single pot to methyl isobutyl ketone using a bifunctional catalyst which comprised palladium and zirconium phosphate (Scheme 20). 

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. 

Continuing the theme of very large-pore zeolite emulators, we also review recent work on aluminum phosphates. While not necessarily layered materials, these systems attempt to fulfill similar requirements as the clays and zirconium phosphates. Important NMR measurements have recently been made on the aluminum phosphates, and this is a current area of interest for many catalytic chemists. 

Segawa et al. (78,791 have examined the catalytic activity of several zirconium phosphates for 1-butene isomerization. They concluded that the e phase remains active even after evacuation at 773 K, while the zirconium phosphate gel and the a form show significant decreases in activity. The pyrophosphate has the highest activity. All three forms dehydrate upon evacuation at temperatures above 1000 K and eventually become the pyrophosphate ZrP207 above 1300 K as the P-OH groups condense to form P-O-P linkages simultaneous with the total loss of catalytic activity for butene isomerization. P MAS-NMR (79] of zirconium phosphate gel, the a form, and the e form of ZrP (Fig. 12) show that the a form has its phosphorus resonance at — 16.6 ppm, while in the e form it occurs at - 21.7 ppm (with reference to H3FK>4 at 0 ppm). The gel shows peaks at - 11.8,... 

An experiment was conducted to demonstrate that the zirconium phosphate catalyst was indeed working in a heterogeneous manner. After one recycle using Zr( )CPC, no significant reduction in catalytic activity was observed (Table 6). 

Table 5 Examples of the Catalytic Applications of Zirconium Phosphates and Its Derivatives... 

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. 

The aim of the present work is to study the influence of the methods of synthesis of silver-containing zirconium phosphates on the composition, stmcture and catalytic activity of materials in the process of ethylene glycol oxidation, and formation of active sites (Ag nanoparticles) on the surface of zirconium-phosphate matrix. 

Sant and Varma (183) found that low concentrations of zirconium lowered the temperature required to reach the maximum yield. Various interpretations of this observation have been put forward either the increase in surface area or the increase in oxygen transport rates can be sufficiently altered by the zirconium to result in high yields of MA at lower temperatures. The studies generally agree that aroimd 1.5% zirconium has the most beneficial effect on the activity, and good catalytic performance could be achieved at lower temperatures (172). One of the reasons for this that has been proposed is that zirconium and titanium both create acidic surface sites on the vanadium phosphate surface. These sites prevent the desorption of reaction intermediates (butene, butadiene, and furan) while facilitating the desorption of the acidic MA. 

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