AVS 56th International Symposium & Exhibition
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA2
On the Role of Pd Ensembles in Selective H2O2 Formation on PdAu Alloys

Monday, November 9, 2009, 2:20 pm, Room N

Session: Formation & Reactivity of Nanoclusters
Presenter: H. Ham, University of Texas at Austin
Authors: H. Ham, University of Texas at Austin
G. Hwang, University of Texas at Austin
Correspondent: Click to Email
Bimetallic Pd-Au alloys have been found to significantly increase catalytic efficiency, compared to the monometallic Pd and Au counterparts, in various reactions including direct synthesis of H2O2 from H2 and O2 and production of vinyl acetate monomers. Recent evidence suggests that the reactivity of bimetallic catalysts would be governed by creation of unique mixed-metal surface sites [the so called ensemble effect] and/or electronic structure change by metal-metal interactions [ligand effect], while mechanisms underlying the alloying effect still remain unclear. Very recently, the role played by Pd monomers in the direct H2O2 synthesis has also been studied using density functional theory calculations, yet detailed reaction mechanisms associated with Pd atomic arrangements are still lacking. In this talk, we will present some recent theoretical results we have on the role of Pd ensembles in determining the selectivity of direct H2O2 synthesis. Using periodic density functional theory calculations, we find that the H2O2 formation selectivity can be governed by the spatial arrangements of Pd and Au surface atoms, particularly the availability of Pd monomers surrounded by less active Au atoms. Our calculations suggest that the large activity difference between Pd and Au atoms is a key factor for selective H2O2 formation, by suppressing O-O bond scission. This work hints the importance of knowing how to properly tailor Au reactivity for achieving wanted reactions, while the relative activities of Au and Pd surface atoms can be a function of subsurface layer composition as well as catalyst size and shape.