Aluminium hydrotalcites

An amorphous layer was observed on the surface of the particles (refer Fig. 5) as analysed by TEM. The possible origin of this amorphous layer can be described by the following hypothesis During the aqueous phase cobalt nitrate catalyst preparation step, the alumina support dissolves and the dissolved aluminium ions can precipitate either as boehmite or may, in combination with cobalt ions, precipitate as a cobalt aluminium hydrotalcite-like layer [16], producing a physically amorphous layer, uniformly covering the sur ce of the bulk support material [15]. It was, however, not possible to characteri2e the observed layer. 

Tert-butylation of phenol with isohutanol over magnesium-aluminium hydrotalcites... 

Magnesium-aluminium hydrotalcites are prepared with Mg/Al atomic ratios 2-7 and characterized by XRD, DTA, surface area measurements and acidity-basicity measurements. The tert-butylation of phenol is carried out on the calcined magnesium-aluminium hydrotalcites using isobutanol in the temperature range of350-500°C. The major products of this reaction are O-tert-butyl phenol and 2-tert-butyl phenol. Along with the normal alklyated products 0-butenyl phenol and 2-butenyl phenols are also obtained. A correlation between the product distribution and the nature of acid-base properties of the catalyst is studied. 

Many convention- acid and base catalysts are being replaced by more eco-fnendly solid catalysts. In the present investigation calcined magnesium-aluminium hydrotalcites are used for the tert-butylation of phenol using isobutanol. The aim of the present work is to correlate the acid-base properties of hydrotalcites with the obtained product distribution. 

To confuse the situation further, differences in the vibration frequencies of M-C bonds in chemisorbed carbon monoxide and M-H bonds in chemisorbed hydrogen, between those found with small platinum particles in NaX zeolite and in magnesium aluminium hydrotalcite, " and those for larger particles or bulk metal, have been interpreted to imply that the metal is negatively charged. It is however difficult to see how a particle can be both negatively charged and electron deficient at one and at the same time. 

Hycite EXM and Sorbacid EXM (Sud-Chemie) are extremely fine magnesium/ aluminium hydrotalcites, for use as co-stabilizers for polyolefins and PVC, respectively. They effectively neutralize acids from catalyst residues or decomposition products of primary and secondary stabilizers. Corrosiveness of polymers is decisively reduced by absorptive immobilization of anions, especially chloride. Sorbacid is mainly used in environmentally friendly and non-toxic formulations free of heavy metals, together with Ca/Zn systems. It has excellent dispersion in small particles, which, with a special surface modification and a refractive index close to that of PVC, gives formulations for transparent applications without any restrictions. 

In 2012, Ravasio and co-workers also reported an additive-free A-alkylation of amines with benzyl and aliphatic alcohols catalyzed by C11/AI2O3 [161]. In 2014, the authors extended the method to the iV-alkylation of anilines with a wide range of alcohols (Eq. 47) [162]. In 2013, Mishra and co-workers reported an additive-free A -aUcylation of primary amines with primary and secondary alcohols catalyzed by copper-aluminium hydrotalcite (CuAl-HT) [163]. 

Likhar PR, Arundhathi R, Kantam ML et al (2009) Amination of alcohols catalyzed by copper-aluminium hydrotalcite a green synthesis of amines. Eur J Org Chem 2009(31) 5383-5389... 

Many inorganic oxides can be manufactured to provide granular, porous materials with high surface areas, which can readily adsorb organic liquids. Preliminary screening of a range of oxides, namely aluminium oxides, titanium dioxides, zinc oxide, hydrotalcites, zeolites and silicas, indicated that the latter two materials were able to retain the largest quantities of biocide. 

The great importance of minerals in prebiotic chemical reactions is undisputed. Interactions between mineral surfaces and organic molecules, and their influence on self-organisation processes, have been the subject of much study. New results from Szostak and co-workers show that the formation of vesicles is not limited to one type of mineral, but can involve various types of surfaces. Different minerals were studied in order to find out how particle size, particle shape, composition and charge can influence vesicle formation. Thus, for example, montmorillonite (Na and K10), kaolinite, talc, aluminium silicates, quartz, perlite, pyrite, hydrotalcite and Teflon particles were studied. Vesicle formation was catalysed best by aluminium solicate, followed by hydrotalcite, kaolinite and talcum (Hanczyc et al., 2007). 

Shen, J., Kobe, J. M., Chen, Y. and Dumesic, J. A. (1994). Synthesis and surface acid/base properties of magnesium-aluminium mixed oxides obtained from hydrotalcites. Langmuir 10, 3902. 

Kooli, F., Rives, V. and Ulibarri, M. A. (1995). Preparation and study of decavanadate-pillared hydrotalcite-like anionic clays containing transition metal cations in the layers. 1. Samples containing nickel-aluminium prepared by anionic exchange and reconstruction. Inorg. Chem. 34, 5114. 

Velu, S. and Swamy, C. S. (1997). Effect of substitution of Fe3+/Cr3+ on the alkylation of phenol with methanol over magnesium-aluminium calcined hydrotalcite. Appl. Catal. A 162, 81. 

The effects of a hydrotalcite (magnesium/aluminium hydroxy carbonate) acid scavenger on the thermal stability of barium/zinc-stabilisedpoly(vittyl chloride) containing zinc pyrithione biocide in various proportions were investigated by heat stability, (fynamic thermal stabiUty and Brabender mastication experiments coupled with colour, anti-bacterial and anti-fungal measurements, and the results are discussed. 12 refs. 

Magnesium-aluminium hydrotaldte is a naturally occurring anionic clay that decomposes reversibly upon calcination at high temperatures to form high surface area basic mixed oxide. To generate the hydrotalcite structure, Al cations replace... 

Some other examples of carbonyl compounds reduced by hydrogen transfer from alcohols arc benzaldehyde (36) on aluminium alkoxides. MgO, zeolites, and LDH s, cyclohexanone [264] over LDIFs or 4-tcrt-butyIcyclohexanonc [110] over calcined hydrotalcites. NaBHA zeolites and KF AI Oi. 

The first crack in this paradigm, however, occurred in 1989. Although not commercially attractive from a conversion and reactivity point of view, Hoechst (1) and Henkel (2) demonstrated that alkoxylation catalysts based on alkali/alkaline-earth metals and calcined hydrotalcites (aluminium-magnesium hydroxy-carbonates), respectively, promoted the ethoxylation of esters. In 1990, Vista Chemical Company (now Sasol North America, Inc.) demonstrated that their proprietary catalyst (activated calcium and aluminium alkox-ides), and similar catalysts, efficiently and effectively ethoxylated a variety of esters (3). That same year. Lion showed that magnesium oxide-based catalysts also worked well (4). Henkel followed with the discovery that hydrotalcites become effective catalysts for esters when combined with co-catalysts such as ethylene glycol, fatty acids and standard alkali catalysts (5, 6). These discoveries effectively launched the development... 

Ross, G. J. and Kodama, H. 1967. Properties of a synthetic magnesium-aluminium carbonate hydroxide and its relationship to magnesium-aluminium double hydroxide, manasseite and hydrotalcite. Amer. Miner. 52 (7/8) 1036-47. 

Hydrotalcite, Mg5A 2(0H)26C03.4H20, is one of the naturally occurring anionic clay minerals (Reichle 1986). The magnesium-aluminium hydroxide octahedra form positively charged layers and are stacked on top of each other. The carbonate ions are located between the layers as interlayer anions. These clays after heat treatment have been found to be catalysts for base catalyzed reactions. 

Walspurger, S Boels, L Cobden, P.D. et al. (2008) The crucial role of the K+-aluminium oxide interaction in K+-promoted alumina- and hydrotalcite-based... 

The second model of the structure is based on the works of Allman and Tailor who identified structures of the minerals (hydrotalcite and manasseite) [28,29] and showed that magnesium and aluminium ions are located in octahedral voids of hydroxide layer. Anions X and water molecules form another layer. Using this approach, Serna assumed on the basis of electron microdiffraction data and X-ray diffraction patterns of powders that the structure of LADH-CO3 obtained by the hydrolysis of aluminium-tri-(sec-butoxide) in hthium carbonate is based on closely packing two-dimensional layer (30 ]. Two thirds of the octahedral voids in this layer are occupied by aluminium cations located in a manner similar to that of gibbsite. The remaining one third of voids is occupied by lithium cations. On... 

X Lamellar phase Nickel Aluminium Carbonate Hydroxide NiAltCOiVOH) (hydrotalcite) [ICDD 00-048-0593]... 

Highly porous hydrotalcite-like film growth on anodised aluminium monoliths... 

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