The direct synthesis of hydrogen peroxide (H2O2) from hydrogen (H-2) and oxygen (O-2) on Pd(1 1 1), Pt(1 1 1), PdH(2 1 1) and Au0.89Pd0.11(2 2 1) catalysts was investigated through the use of Density Functional Theory calculations. Three formation steps and their competing (decomposition) counterparts were examined on all model surfaces: O-2 hydrogenation versus O-2 dissociation, OOH hydrogenation versus OOH dissociation, and H2O2 desorption versus H2O2 dissociation. We have found that as we change the surface from Pd to Pt to Au, the step which governs the non-selective formation of water shifts from O-2 dissociation to OOH dissociation to H2O2 decomposition. (C) 2010 Elsevier B.V. All rights reserved.