Study of the citral/acetone reaction on MgyAlOx oxides: Effect of the chemical composition on catalyst activity, selectivity and stability

V.K. DÍEZ; J.I. DI COSIMO; C.R. APESTEGUÍA

APPLIED CATALYSIS A-GENERAL

Elsevier

Año: 2008 vol. 345 p. 143 - 151

0926-860X

The liquid-phase citral/acetone reaction was studied on MgO, Al2O3 and MgyAlOx mixed oxides with Mg/Al molar ratios of 0.11-3. The density, strength and nature of surface acid sites were determined by NH3 thermodesorption and FTIR of pyridine.   The surface basic properties were probed by temperature programmed desorption of CO2.  The rate of the citral/acetone cross-aldolization to pseudoionones increased linearly with the density of strong O2- base sites. Thus, the pseudoionone synthesis was efficiently promoted on MgO and Mg-rich MgyAlOx samples. In contrast, the initial rate of the parallel acetone self-condensation reaction augmented with the density of Lewis acid sites, and diacetone alcohol was more rapidly formed on Al2O3 and Al-rich MgyAlOx samples. Differences in the reactant adsorption strength on surface Al3+ sites may explain the observed differences between the acid-catalyzed mechanisms of cross- and self-aldolization reactions. In-situ catalyst deactivation was determined by performing two consecutive catalytic runs.  The activity decay of MgyAlOx samples during the citral/acetone reaction was between 15-20 %, irrespective of the catalyst composition.