Layered double hydroxides coprecipitation

One problem associated with the peroxotungstate-catalyzed epoxidation system described above is the separation of the catalyst after the completed reaction. To overcome this obstacle, efforts to prepare heterogeneous tungstate catalysts have been conducted. De Vos and coworkers employed W catalysts derived from sodium tungstate and layered double hydroxides (LDH - coprecipitated MgCU, AICI3, and NaOH) for the epoxidation of simple olefins and allyl alcohols with... 

It has been pointed out that these pillared intercalates are intrinsically difficult to synthesize in highly crystalline form because the layered hosts are basic, whereas most heteropolyacids are acidic and tend to decompose. Narita et al. (392) tried direct synthesis of a heteropolyanion-pillared layered double hydroxide by a coprecipitation reaction of Zn2+ and A1J+ ions in the presence of a moderately acidic lacunary Keggin anion, a-SiWn039 XRD of the product showed a basal spacing of 14.6 A, which corresponds to a gallery height of 9.9 A. The surface area was found to be 97 m2 g, which is three times that of the layered double hydroxide. 

Narita, E., Kaviratna, P. D. and Pinnavaia, T. J. (1993). Direct synthesis of a polyoxometalate-pillared layered double hydroxide by coprecipitation. J. Chem. Soc., Chem. Commun., 60. 

Layered double hydroxides are typically synthesized from coprecipitation of mixed metal cations by base titration either with or withont hydrothermal treatment which nsnally enhances crystalline properties." " Becanse contamination with airborne carbonate ions freqnently occurs during synthesis procedures, special caution is needed to prepare carbonate-free LDHs. On the other hand. 

The photoprocesses of ruthenium tris(4,7-diphenyl-l,10-phenanthrolinedi-sulfonate) (Ru(BPS)3" ) intercalated in a layered double hydroxide (LDH) has been studied (102). The compound was prepared by coprecipitation of Mg/Al LDH from an aqueous NaOH solution containing the metal chloride salts and Ru(BPS)3" with hydrothermal treatment. Multiexponential decay profiles were observed. From the effects of surface dilution by Zn(BPS)3" on luminescence, the decay profile has been attributed to self-quenching processes similar to those for [Ru(bpy)3] -smectite systems. 

It should be noted that magnesium aluminum layered double hydroxides (MgAl-LDHs) have also been widely used as flame retardants for polymer materials. Similarly, MgAl-LDHs can be synthesized by reaction of aluminum and magnesium salts as precursor and sodium hydroxide as precipitator via the coprecipitation method and other preparation routes. ... 

Morozkova V.E., Tomilov N.P., Berger A.S. About double hydroxides nickel and aluminium of layered stmcture. 111. Sorption of water vapour by phase variety of nickel and aluminium hydroxides. Izvestiya SO AN SSSR, ser. chem. nauk, 1984 6 50-57. Tomilov N.P., Deviatkina E.T. Synthesis of MgAl204 from coprecipitated hydroxides. Neorgan. Materiah 1990 26 2556-61. 

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