The effect of oxygen pre-treatment of Ag/SiO2 Catalysts used in the acrolein hydrogenation has been investigated from sub-atmospheric (266 mbar) to 10 bar reaction pressure. The pre-treatment has a profound influence on the overall hydrogenation activity, inasmuch the activity increased two- to threefold. Oxygen pre-treatment also enhanced the selectivity towards the desired allyl alcohol. The beneficial effect of oxygen pre-treatment is ascribed to the formation of electronically modified Ag and/or morphology changes of the nanoparticles as no modification in particle size or dispersion was found. (c) 2008 Elsevier B.V. All rights reserved.