Several magnesia and zirconia systems were synthesized through the sol-gel process (calcination temperature in the 175-600 degrees C range) and tested for liquid and gas-phase Meerwein-Ponndorf-Verley reduction of crotonaldehyde with 2-propanol. In the liquid phase, only zirconia systems were active, probably because carbonates and water "poison" active sites in basic magnesia. Moreover, the more surface OH groups were present in zirconia solids, the higher the activity exhibited. As far as reactions in the gas phase are concerned, both zirconia and magnesia solids were active, the latter exhibiting higher conversions at the same reaction temperatures. Furthermore, for MgO solids selectivity to crotyl alcohol increases with the reaction temperature which suggests that either new active sites were "in situ" created or the existing ones were unblocked and made accessible to the reactants. All in all, selectivities to crotyl alcohol of ca. 62% at 16% conversion were obtained for more active systems ZrO2-200 and ZrO2-250 in the liquid phase whereas values above 85% at 50% conversion were achieved on MgO solids in the gas-phase. (C) 201 1 Elsevier B.V. All rights reserved.