Layered double hydroxides exchange reactions

The dispersion and solid-state ion exchange of ZnCl2 on to the surface of NaY zeolite by use of microwave irradiation [17] and modification of the surface of active carbon as catalyst support by means of microwave induced treatment have also been reported [18]. The ion-exchange reactions of both cationic (montmorillonites) and anionic clays (layered double hydroxides) were greatly accelerated under conditions of microwave heating compared with other techniques currently available [19.]... 

The oxidation of sulfides to sulfones has been the subject of extensive studies, since sulfones are useful synthons for the construction of various chemically and biologically significant moleculesJ Recently, a new catalytic system has been developed by exchanging potassium osmate onto chloride-saturated layered double hydroxides (Figure 9.1), which we have shown to be an efficient catalyst for the direct oxidation of sulfides to sulfones, using molecular oxygen as the stoichiometric oxidant and with delivery of two oxygen atoms simultaneously to the sulfide, reminiscent of olefin dihydroxylation reactions. 

Meyn, M., Beneke, K., and Legaly, G. Anionic-exchange reactions of layered double hydroxides, Inorg. 

Fogg, A. M., Dunn, J. S. and O Hare, D. (1998). Formation of second-stage intermediates in anion-exchange intercalation reactions of the layered double hydroxide [LiAl2(OH)6]Cl, H20 as observed by time-resolved, in situ X-ray diffraction. Chem. Mater. 10, 356. 

The COj species in the HT interlayer could be exchanged with OH ions by calcination at 723 K and hydration at room temperature. A spinel phase of Mg-Al mixed oxide obtained after the calcination transforms into the original layered structure during the hydration. This reconstruction is known as the memory effect of HT materials. The reconstructed HT catalyzed the Knoevenagel condensation of various aldehydes with nitriles in the presence of water [119]. The reconstracted HT also showed an aqueous Michael reaction of nitriles with a,p-unsaturated compounds. The layered double-hydroxide-supported diisopropylamine catalyzed the Knoevenagel condensation of aromatic carbonyl compounds with malononitrile or ethyl cyanoacetate [120]. This solid base could be recycled at least four times, and exhibited activity for aldol, Henry, Michael, transesterification, and epoxidation of alkenes. 

A tungstate-exchanged Mg-Al layered double hydroxide (LDH) was employed to catalyze oxidation of aliphatic tertiary amines to N-oxides by 30% aqueous H2O2 (Table 8.8) [117]. The reaction takes 1-3 h at room temperature. The use of dode-cylbenzenesulfonic acid sodium salt as an additive increased the rate of the oxidation by a factor of 2-3 except for N-methyl morpholine. An advantage with the LDH-W04 catalyst is that it can be reused. 

Conductive electrodes based on metal oxide, e.g., indium-tin oxide (TTO), are widely used in electrochemistry as a support for surface modification with the goal to develop sensors with electrochemical transduction or combined spectroscopic and electrochemical responses or electrochemiluminescence. Inorganic thin films can also be prepared from the assembly of two-dimensional layered inorganic solids, such as cationic clays and layered double hydroxides (LDHs, also defined as anionic clays). These materials can be used to preconcentrate species on the basis of ion-exchange reactions and applied to heavy metal determination or for the detection of organic pollutants. 

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