Hydrotalcite properties

Mg/Me (Me=Al, Fe) mixed oxides prepared from hydrotalcite precursors were compared in the gas-phase m-cresol methylation in order to find out a relationship between catalytic activity and physico-chemical properties. It was found that the regio-selectivity in the methylation is considerably affected by the surface acid-basic properties of the catalysts. The co-existence of Lewis acid sites and basic sites leads to an enhancement of the selectivity to the product of ortho-C-alkylation with respect to the sole presence of basic sites. This derives from the combination of two effects, (i) The H+-abstraction properties of the basic site lead to the generation of the phenolate anion, (ii) The coordinative properties of Lewis acid sites, through their interaction with the aromatic ring, make the mesomeric effect less efficient, with predominance of the inductive effect of the -O species in directing the regio-selectivity of the C-methylation into the ortho position. 

In summary, the Zn-Al and Zn-Ga based-hydrotalcites were found as very effective supports for docking a Rh(TPPTS)3Cl complex. The process was carried out via ionic exchange and occurred without any damage of die support structure or of the complex. The resulted catalysts were found to catalyze the cyclization of acetylenic carboxylic acids to the corresponding 5-membered ring heterocycles in good to excellent yields. The basic properties of the support also allow a clean and selective reaction of unsubstituted acetylenic carboxylic acids. 

Structural and textural properties of zinc(II)-chromium(III) spinel oxides prepared using a hydrotalcite-like compound... 

However, no leaching effect was observed with hydrotalcites in their hydroxide or mixed carbonate-hydroxide form.[21] Modifications of their basic properties lead to an increase in the selectivity to fructose to nearly 100%, but once again at a glucose conversion lower than 20%. 

HYDROTALCITES AND RELATED COMPOUNDS Preparation and Catalytic Properties... 

Cavani, F., Trifiro, F. and Vaccari, A. Hydrotalcite-type anionic clays preparation, properties and applications, Catal. Today, 1991, 11, 173-301. 

Corma, V., Fomes, V., Martin-Aranda, R. M. and Rey, F. Determination of base properties of hydrotalcites condensation of benzaldehyde with ethyl acetoacetate, J. Catal., 1992, 134, 58-65. 

Valente, J. S., Figueras, F., Gravelle, M., Kumbhar, P., Lopez, J. and Besse, J. P. Basic properties of the mixed oxides obtained by thermal decomposition of hydrotalcites containing different metallic compositions, J. Catal., 2000, 189, 370-381. 

Wang, X. and Zhang, Q., Effect of hydrotalcite on the thermal stability, mechanical properties, rheology and flame retardance of poly(vinyl chloride), Polym. Int., 53, 698-707, 2004. 

Yong-zhong, B., Zhi-ming, H., Shen-xing, L., and Zhi-xue, W., Thermal stability, smoke emission, and mechanical properties of poly(vinyl chloride)/hydrotalcite nanocomposites, Polym. Deg. Stab., 2008, 93, 448M55. 

Hydrotalcite (HT) is a clay mineral which on crushing becomes a fine powder, similar to talc. It is a hy-droxycarbonate of Mg and A1, of the general formula Mg6Al2(0H)i6C03 - 4H20, and occurs in nature in foliated and controlled plates and/or fibrous masses. Anionic clays of the HT type have been of importance in catalysis since 1970. Their interesting properties for catalytic applications are ... 

Cavani F, Trifiro F, Vaccari A. Hydrotalcite-type anionic clays Preparation, properties and applications. Catalysis Today. 1991 11 (2) 173—301. 

Miyata, S. (1983). Anion-exchange properties of hydrotalcite-like compounds. 

Miyata, S. (1980). Physico-chemical properties of synthetic hydrotalcites in relation to composition. Clays Clay Miner. 28, 50. 

Sato, T., Fujita, H., Endo, T., Shimada, M. and Tsunashima, A. (1988). Synthesis of hydrotalcite-like compounds and their physicochemical properties. React. Solids 5, 219. 

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. 

Costantino, U., Marmottini, F., Nocchetti, M. and Vivani, R. (1998). New synthetic routes to hydrotalcite-like compounds - characterisation and properties of the obtained materials. Eur. J. Inorg. Chem., 1439. 

Velu, S., Sabde, D. P., Shah, N. and Sivasanker, S. (1998). New hydrotalcite-like anionic clays containing Zr4+ in the layers synthesis and physicochemical properties. Chem. Mater. 10, 3451. 

Miyata, S. and Kumura, T. (1973). Synthesis of new hydrotalcite-like compounds and their physico-chemical properties. Chem. Lett., 843. 

Dumitriu, E., Hulea, V., Chelaru, C., Catrinescu, C., Tichit, D. and Durand, R. (1999). Influence of the acid-base properties of solid catalysts derived from hydrotalcite-like compounds on the condensation of formaldehyde and acetaldehyde. Appl. Catal. A 178, 145. 

Shen, J. Y., Tu, M. and Hu, C. (1998). Structural and surface acid/base properties of hydrotalcite-derived MgAlO oxides calcined at varying temperatures. J. Solid State Chem. 137, 295. 

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