Direct Synthesis of H2O2 on AgPt Octahedra: The Importance of Ag-Pt Coordination for High H2O2 Selectivity

H2O2 production by direct synthesis (H-2 + O-2 -> H2O2) is a promising alternative to the energy-intensive anthraquinone oxidation process and to the use of chlorine for oxidation chemistry. Steady-state H2O2 selectivities are approximately 10-fold greater on AgPt octahedra (50%) than on Pt nanoparticles of similar size (6%). Moreover, the initial H2O2 formation rates and selectivities are sensitive to the fractional coverage of Pt atoms and their location on the surfaces of AgPt octahedra, which can be controlled by exposing these catalysts to either CO or inert gases at 373 K to produce Pt-rich (16% initial H2O2 selectivity) or Pt-poor (36% initial H2O2 selectivity) surfaces. Increasing the coordination of Pt to Ag significantly modifies the electronic structure of Pt active sites, which is reflected by a shift in the v(C=0) singleton frequency in (CO)-C-13 from 2016 cm(-1) on Pt to similar to 197S cm(-1) on AgPt. These bimetallic AgPt catalysts present lower activation enthalpies (Delta H-not asymptotic to) for H2O2 formation (29 kJ moll on Pt to 5 kJ mol(-1) on AgPt) but a lesser decrease for H2O formation (26 kJ mol(-1) on Pt to 16 kJ mori on AgPt). Comparisons of H2O2 selectivities, AW values, and differences among the (CO)-C-13 singleton frequencies show that a combination of coordinating Ag to Pt and inducing strain modifies the electronic structure of individual Pt atoms, causing them to bind species (e.g.,CO) more strongly than on Pt nanoparticles. Yet the dramatic increase in the number of isolated Pt atoms increases H2O2 selectivities by decreasing the number of Pt atom ensembles of sufficient size to cleave O-O bonds and form H2O.