Layered double hydroxides precursors

Xia, S., Yuan, Z., Wang, L., et al., 2011. Hydrogenolysis of glycerol on bimetallic Pd-Cu /solid-base catalysts prepared via layered double hydroxides precursors. Applied Catalysis A 403,173-182. 

Evans, D.G. and Duan X. (2006) Preparation of layered double hydroxides and their application as additives, polymers, as precursors to magnetic materials and in biology and... 

Layered silicate clays intercalated by pillaring poly-oxocations are precursors to an important class of mi-croporous catalysts. Smectite clay was the only host structure known to be pillarable by purely inorganic oxo ions. Recently, layered double hydroxides (LDH) pillaring oxo ions were reported by Pinnavaia and coworkers [79, 80]. 

Chibwe, K. and Jones, W. (1989). Synthesis of polyoxometalate-pillared layered double hydroxides via calcined precursors. Chem. Mater. 1, 489. 

Rocha, J., del Arco, M., Rives, V. and Ulibarri, M. A. (1999). Reconstruction of layered double hydroxides from calcined precursors a powder XRD and Al-27 MAS NMR study. J. Mater. Chem. 9, 2499. 

Dimotakis, E. D. and Pinnavaia, T. J. (1990). New route to layered double hydroxides intercalated by organic-anions - precursors to polyoxometalate-pillared derivatives. Inorg. Chem. 29, 2393. 

The anionic polyoxometalates comprise a much larger class of metal oxide-based pillaring agents (18). It was proposed that hydrotaldtes (also referred to as layered double hydroxides, or LDHs) would be suitable host materials for pillaring with polyoxometalates. Subsequently, a route for synthesizing isopol3rmetalate-pillared hydrotalcites via organic-anion-pillared precursors was developed (19-20). 

Complex precipitates, such as layered double hydroxides, are frequently prepared as precursors of oxide catalysts. Hydrotalcite is a hydrated hydroxy-carbonate mineral with the formula Mg,sAl2(0H)i6C03-4H20. It represents the better known and most popular member of a family of layered double metal hydroxide com-... 

Names of precursors, intermediates and carbons are denoted by a mixture of the starting material, the procedure this starting material has undergone and important experimental conditions. For example, LSS1C673DC means Layered double hydroxide of StyreneSulfonate batch 1, Carbonised at 670 °C for 3 hours, subsequently Demineralised in HCF. 

Hydrogenations of acetonitrile and pentylnitrile (valeronitrile) in gas and liquid phases respectively were carried out on catalysts obtained from Ni/Mg/Al layered double hydroxides (LDHs) precursors of various Mg/Ni molar ratios. Their catalytic properties were compared with those of a commercial Ni/Al203 catalyst. Selectlvities to primary amines, higher than 90% were obtained on catalysts with Mg/Ni molar ratios in the range 0.3-1. This behaviour was correlated with the acido-basic properties of the solids characterized by TPD of NH3 and microcalorimetry of monoethylamine adsorption. Both studies show that upon Mg addition, the surface acidity, which is responsible for secondary amine formation decreases. 

The layered double hydroxides have been of interest as anion exchangers, basic catalysts, and catalyst precursors. Pillared derivatives of the type discussed earlier for the clays have been synthesized by ion exchange with polyoxometallate anions but have lower thermal stability. Several authors have reported synthesis of layered double hydroxides pillared with the Vio028 ion by direct ion exchange or by techniques that involve preswelling the layer structure with an organic anion. For example, the terephthalate anion was used in the synthesis ofVio028 and Mo7 024 intercalated phases. 

Alcjandrc, A., Medina, F., Rodriguez, F., Salagre, P., Ccslcros, Y. and Suciras. J. E. (2001). Cu/Ni/AI layered double hydroxides as precursors of catalysts for the wet air oxidation of phenol aqueous solutions. Applied Catalysis B Environmental, 30, 195-207. 

Caija, G., Nakamura, R.. Aida. T. and Niiyama, H. (2003). Mg-V-AI mixed oxides with mesoporous properties using layered double hydroxides as precursors catalytic behavior for the process of ethylbenzene dehydrogenation to styrene under a carbon dioxide flow. 7. Coto/., 218, 104-110. 

The hydroxycarbonate precursors showed dif action patterns consistent with the layered double hydroxide structure proposed for hydrotalcite-like compounds, i.e., brucite-like sheets formed by OH groups and cations (Mg and AP ) in octahedral coordination. Water molecules and charge-compensating COs anions are located in the interlayers. The hydrotalcite-like precursor composition is [Mg,, .Al,(0H)2] (C03), . mH20 with r = Al/(A1+Mg) the stoichiometric hydrotalcite compound, Mg6Al2(0H)i6C03.4H20, is obtained for r = 0.25. Upon thermal decomposition at 673 K, the hydroxycarbonate precursors lose... 

Narita, E., Kaviratna, P., and Pinnavaia, T. J. 1991. Synthesis of Heteropolyoxometalate Pillared Layered Double Hydroxides via Calcined Zinc-Aluminium Oxide Precursors. Chem. Lett. 805-08. 

Recently, we reported that thin films with nanocrystals such as boehmite (AlOOH) [7-10], Al-Zn layered double hydroxide (LDH) [11], and anatase [12] were prepared through hot water treatment of the gel films at temperatures less than 100 C. In this process, precursor gel films prepared using the sol-gel process were immersed only in hot distilled water under ambient atmosphere at temperatures lower than 100 C. Although studies of oxide film formation from solution are usually based on the precipitation of crystals from a saturated solution of the precursor [1-6], in the present process, precursor amorphous gel films prepared using the sol-gel process are immersed in hot distilled water to form nanocrystals on the thin film surface. 

L. Z. Qiu, W. Chen, and B. J. Qu, Exfoliation of layered double hydroxide in polystyrene by in-situ atom transfer radical polymerization using initiator-modified precursor. Colloid and Polymer Science, 283 (2005), 1241-5. 

The single-pot biomimetic synthesis of chiral diol 27, mediated by the recyclable trifunctional catalyst, Na2PdCl4-K20s04-Na2W04 embedded in a matrix of layered double hydroxides, resulted in an efficient, low cost process. This protocol provided the desired prochiral olefin from Heck precursors and the in situ recycling of NMM to NMO. The whole process starts with cheap precursors and minimizes the number of unit operations. Other similar broad, interdisciplinary studies which led to an extraordinarily selective solution to the splitting of the amide bond in a mixture of compounds from a natural source will be considered in the next section. 

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