Double layer hydroxides

Double layer hydroxides M6Al2(0H)16C03-nH20 M=Mg, Zn... 

Isomerization of jS-isophorone to a-isophorone has been represented as a model reaction for the characterization of solid bases 106,107). The reaction involves the loss of a hydrogen atom from the position a to the carbonyl group, giving an allylic carbanion stabilized by conjugation, which can isomerize to a species corresponding to the carbanion of a-isophorone (Scheme 9). In this reaction, zero-order kinetics has been observed at 308 K for many bases, and consequently the initial rate of the reaction is equal to the rate constant. The rate of isomerization has been used to measure the total number of active sites on a series of solid bases. Figueras et al. (106,107) showed that the number of basic sites determined by CO2 adsorption on various calcined double-layered hydroxides was proportional to the rate constants for S-isophorone isomerization (Fig. 3), confirming that the reaction can be used as a useful tool for the determination of acid-base characteristics of oxide catalysts. 

Hydrotalcite Hydrotalcite (Mg6Al2(C03)(0H)i6 4H20) and other double-layered hydroxide compounds may effectively sorb As(V) from water. Hydrotalcites remove As(V) through sorption and/or exchanges with interlayer anions. The minerals may also be heated (calcinated) until most carbonate anions leave the interlayers. The calcinated hydrotalcites are then placed in water, where the vacant interlayers can sorb anions, including As(V) oxyanions (Yang et al., 2005, 6805). 

Jiang, J.-Q., Xu, Y., Quill, K. et al. (2007) Laboratory study of boron removal by Mg/Al double-layered hydroxides. Industrial and Engineering Chemistry Research, 46(13), 4577-83. 

The reaction of benzaldehyde with ethanol in the presence of MgO, CaO, and mixed oxides obtained by calcination of double layered hydroxides was investigated by Aramendia et a/.1851 in liquid phase. CaO was found to be the most active catalyst for the process. 

A charged support, double layered hydroxide, that can be described by the general formula, Mgi xAlx(OH)2Cl zH20, was used to immobilise [PdCl4]2-/811 While results with this catalyst were only poor in A-methyl pyrrolidinone, good conversion and selectivity was obtained in [(C4)4N]Br with arylchlorides as substrates. By employing microwave irradiation coupling between chlorobenzene and styrene afforded the desired product in 95% yield within 30 minutes. The products were isolated by distillation and the catalytic activity remained essentially stable for at least 5 runs. 

Cobalt Clays and Double-Layered Hydroxides as Fischer—Tropsch Catalysts... 

BRUCEETAL. Cobalt Clays Double-Layered Hydroxides... 

Layered Cobalt Hydroxides. The above results demonstrate the importance of the interlayer Co rather than the framework cobalt, in forming the required metallic Co catalyst. A structure with optimal catalytic activity would consist of one where there were only Co/Al hydroxide sheets, a structure closely approximated to by the hydrotalcite series of double layered hydroxides. 

SCHEME 13.6 Sulfite anion and aldehyde adduct formation. A possible concentration process in double-layer hydroxide minerals such as Mg2Al(0H) [S03H (H20)2]. 

Pitch, S, Krishnamurthy, R, Arrhenius, G, Concentration of simple aldehydes hy sulfit-containing double-layer hydroxide minerals imphcation forbiopoesis, Helv. Chim. Acta, 83,2398-2424,2000. 

P-26 - Catalytic properties of Fe-Co double layered hydroxides synthesised with beta zeolite for toluene oxidation... 

The pol5mier nanocomposite field has been studied heavily in the past decade. However, polymier nanocomposite technology has been around for quite some time in the form of latex paints, carbon-black filled tires, and other pol5mier systems filled with nanoscale particles. However, the nanoscale interface nature of these materials was not truly understood and elucidated until recently [2 7]. Today, there are excellent works that cover the entire field of polymer nanocomposite research, including applications, with a wide range of nanofillers such as layered silicates (clays), carbon nanotubes/nanofibers, colloidal oxides, double-layered hydroxides, quantum dots, nanocrystalline metals, and so on. The majority of the research conducted to date has been with organically treated, layered silicates or organoclays. 

In this method the silicates are formed inside of the polymer matrix. To obtain this, an aqueous solution containing polymer and sUicate building blocks is necessary. The polymers help to form the nucleation by the self-assembly forces therefore it produces a double-layer hydroxide-based nanocomposite. 

The incorporation of intercalated double layer hydroxide nanoparticles acted as nucleating agent. They significantly accelerated the PET noiusothermal crystallization process, but had little effect on the three-dimensional growth pattern of sphenrlites. ... 

Breuer, W., Raths, H. C. 1994. Hydrophobized double layer hydroxide compounds. U.S. Patent 5,326,891. 

At this time the technique seems to be limited by a lack of widespread availability of solid-state NMR equipment and the need to use the same batch of clay each time. If a different clay is used, it may contain a different fraction of paramagnetic iron, which will influence the relaxation time. Thus, one cannot compare samples from different suppliers or even from the same supplier obtained at a different time. The technique is also limited to those materials that contain a paramagnetic species, which can facilitate proton relaxation montmorUlonite and other natural clays that contain iron would be acceptable, but double-layered hydroxides and synthetic clays (or even layered silicas, such as magadiite or kenyite) could not be analyzed by this technique. 

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