The hydrogenation of acrolein on supported gold catalysts has been used as test reaction to study several aspects of structure sensitivity, i.e., the dependence of activity and selectivity on the size of gold particles. We focused our work on the influence of the geometrical configuration of the supported gold nanoparticles, namely the occurrence of multiply twinned particles (MTPs) and the degree of rounding. A higher number of MTPs resulted in a lowering of selectivity to the desired product, allyl alcohol, as well as a lowering of the turnover frequency. The higher amount frequency of a gold catalyst supported on TiO2 compared to ZrO2 is attributed to a higher degree of rounding of the former. (C) 2003 Elsevier Science (USA). All rights reserved.