Selective liquid-phase hydrogenation of citral over supported palladium

Citral in the liquid phase was reduced in a low-pressure hydrogenator by using catalysts consisting of palladium supported on (a) a mixed 80:20 SiO2/AlPO4 system and (b) sepiolite from Vallecas (Madrid, Spain), A kinetic study provided the reaction orders in the substrate concentration and hydrogen pressure. Experimental variables such as temperature, hydrogen pressure and the type of solvent were adjusted in order to optimize the reduction process. The presence of additives of the Lewis acid type such as FeCl2 was found to considerably alter the hydrogenation mechanism; under these conditions, the selectivity proved strongly dependent on the Fe2+/Pd atomic ratio, The reaction products were characterized by using gas chromatography in combination with mass spectrometry, (C) 1997 Academic Press.