Abstract

In this work are summarized the results obtained in the thymol hydrogenation using Pd/MgO catalyst. The catalyst was prepared from a colloidal dispersion of Pd in 2-propanol using the SMAD ( Solvent Metal Atom Dispersion) methodology. The catalyst was characterized by means of Transmission Electron Microscopy (TEM) and by chemisorption of hydrogen (metallic area and dispersion). The particles show a bimodal distribution in the histogram of particle distribution with a range of particle size between 11 and 16.6 nm. The catalyst metallic area was 26m2/g with a 5.8 % dispersion. The products obtained from thymol hydrogenation were menthone and isomenthone. The catalyst was not able to hydrogenate the carbonyl group and did not produce the menthol and /or isomers. The different temperatures (80, 100, 125 and 150ºC) only produce an effect in the catalyst activity, but not in the selectivity. The same results were obtained with increase in pressure (3, 5, 7 and 10 bars) and the charge catalyst (3, 7, 10 and 20%) was used. The studies were carried out with different thymol amounts over the same catalyst, and demonstrated no change in the activity. This reveals that the catalyst is poisoned most probably by unreacted thymol. The addition of a promotor (Fe+3) to activate the carbonyl group, allows the obtention of a mixture of menthol isomers. The Pd/MgO catalyst is more active than Pd/C and Pd/Al2O3. This demonstrates that the support plays an important role, however, the Pd is not able to hydrogenate the carbonyl group in menthone or isomenthone.