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Formation of active sites in thermally treated hydrotalcite-based catalysts for acetone aldolization

Kuśtrowski P., Sułkowska D., Chmielarz L., Paczyńska J., Dziembaj R.

Polish Journal of Chemical Technology

2005

Vol. 7, nr 1

33-37

Mg-AI hydrotalcite containing CO3(2-) and NO3(-) as interlayer anions was synthesized according to the coprecipitation method at constant pH (9.0) and temperature (50°C), and then transformed into mixed metal oxides by calcination at 450, 500, 550 or 600°C for 8 h. The as-prepared hydrotalcite-like sample was characterized with respect to its structure (XRD), chemical composition (XRF, elemental analysis) and thermal stability (EGA-MS). Moreover, the textural features of the thermally activated hydrotalcite were examined using low-temperature (77 K) sorption of N2. Changes in the acid-base properties of the precursor calcined at different temperatures were studied by means of temperature-programmed desorptions of NH3 and CO2. It was found that the hydrotalcite-like sample calcined at 450°C, containing a part of non-decomposed interlayer anions, showed a rather low concentration of acidic and basic surface sites. The increase in the calcination temperature caused the removal of the interlayer anions, and an increase in the concentration and strength of the acidic and basic surface centers. The formation of high number of acid/ base surface sites resulted in raising the catalytic activity of the calcined hydrotalcites in the liquid-phase aldol condensation of acetone.

Production of isophorone by the vapour-phase self-condensation of acetone over the hydrotalcite-derived catalysts

Kuśtrowski P., Sułkowska D., Chmielarz L., Cap S.

Polish Journal of Chemical Technology

2004

Vol. 6, nr 4

41-46

The magnesium-aluminum precursor with the structure of hydrotalcite, confirmed by XRD and FTIR, was transformed into mixed metal oxides by a thermal activation at 450, 500, 550 or 600°C for 16 h. The obtained catalysts were characterized with respect to their textural properties (surface area, total porosity and pore size distribution) and used in the gas-phase aldolization of acetone. The effect of reaction temperature and calcination conditions on the catalytic performance was studied. The highest initial conversion of acetone (87.1%) with the selectivity to isophorone of 89.7% was measured for the hydrotalcite-derived Mg-Al oxides calcined at 600°C in the reaction carried out at 240°C.