Highly selective limonene conversions to p-cymene in short reaction times were achieved under "solvent free" conditions over mesoporous silica-alumina supports heated by microwave irradiation. An increase in the silica content of these mixed oxides led to increases in the specific surface area, porosity (pore size and volume) and the surface acidity. The conversion and selectivity of limonene to p-cymene under microwave irradiation was also found to rise as the silica content in these mixed oxides was increased. By careful choice of the solid and reaction parameters the activities for the conversion of limonene and selectivity to p-cymene (used as an intermediate in fine chemical syntheses) could be fine tuned. Results are presented under both dry media and reflux conditions. (C) 2007 Elsevier B.V. All rights reserved.