The hydrogenation of acrolein was studied on a series of silica-supported silver catalysts with various particle sizes (1-9 nm). Particle sizes were determined by EXAFS and confirmed by TEM as well. The selectivity to allyl alcohol (as opposed to propanal) and turnover frequency increased with increasing particle size. The results are somewhat unusual in that the most active catalyst is also the most selective. Increasing the total pressure from 1 to 5 atm was also found to increase the selectivity and decrease the activation energy. The results suggest that the orientation of acrolein on flat surfaces with high coverage is desirable for high selectivity and high activity. However, the selectivity to allyl alcohol decreases with increasing conversion due to the isomerization of allyl alcohol to propanal. (c) 2012 Elsevier Inc. All rights reserved.