Tetra alumina-supported

T. Cserhati, A. Kosa and S. Balogh, Quantitative structure-retention relationship study of tetra-zolium salts on alumina support. Biomed. Chromatogr., 12 (1998) 61-64. 

Certain manganese porphyrins adsorbed on silica or alumina, or intercalated in different mineral matrices such as montmorillonite, are also very efficient in alkane hydroxylation.150 151 Alcohol yields and alcohol ketone ratios are remarkably higher than those obtained with the corresponding soluble manganese porphyrins. Manganese tetra(4-Al-methylpyridiniumyl)porphyrin supported on montmorillonite, for instance, is efficient in the hydroxylation of compounds of low reactivity such as n-pentane and n-heptane.151... 

In the method described by several researchers [30,94-101], a gold precursor (e.g., gold acetate, hydrogen tetranitratoaurate, chloroauric acid) is added to a sol solution of the desired support (such as alumina, titania, etc.). This sol is previously made by the mixing of a support precursor (e.g., aluminium tri-sec-butoxide or aluminium isopropoxide for alumina, tetrabutoxy-titanium for titania, tetra-ethyl-orf/io-silicate for silica) with water and ethanol or methanol and/or nitric acid. 

Silica support modification in the case of catalyst B was perfi)rmed as reported earlier by Beguin et al. [22], prior to the catalyst preparation, by means of a non-aqueous slurry phase impregnation step using Tetra Ethoxy Ortho Silicate (TEOS) as precursor. TEOS dissolved in dry ethanol was used as impregnation solution. The alumina powder was added and after impregnation, the slurry was dried at 60°C under vacuum for 6 hours. The dried modified support was calcined in air at 500°C for 2 hours [4], The silica level was found to be 2.5 Si atoms/nm fresh support. 

The reaction is usually performed at low temperature, typically 20-50 °C, in order to avoid a reaction of the tin complex with the hydroxy groups of the support, as shown by solid-state C CP-MAS NMR. Indeed, it has been shown that tetra-n butyl tin or tributyl tin hydride reacts, above ca. 150 °C with the hydroxy groups of silica, siUca-alumina or alumina with formation of a surface grafted =M-0-Sn(n- 4119)3 fragment and evolution of butane or hydrogen [61, 109-111] (Scheme 18.5). 

Silica membranes have only recently been synthesized. Silica forms sols and gels very easily through both routes. Larbot et al. [45] reported a Si02 membrane (5 pm thick) prepared through a colloidal route. This membrane was supported on an alumina layer (0.2 pm pore size) and had pore sizes from 6 to 10 nm. The polymeric route can start from a tetra-methoxysilane leading to crack-free layers up to 20 nm with grain sizes of 6 X 2nm [24]. 

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