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Cooperative O-atom binding produces the active configuration for OH formation in high-temperature catalytic hydrogen oxidation

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Nov 29, 2024 version files 1.31 MB

Abstract

Much effort in heterogeneous catalysis has gone into identifying “active sites” responsible for reactivity, knowledge of which could make predictive first principles theories useful for rational catalyst design. A major challenge arises since the structures that account for catalytic acceleration of reactivity may only form while reacting at high temperatures and pressures. This makes experimental tools that have proven useful in identifying active sites in ultrahigh vacuum and at low temperature of dubious utility. In this work, we present velocity-resolved kinetics (VRK) measurements for catalytic hydrogen oxidation on Pd over a wide range of surface concentrations and at high temperatures. The rates exhibit a complex dependence on oxygen coverage and step density, which can only be explained by a kinetic model derived from density functional theory (DFT) used in combination with transition-state theory (TST), when one includes a cooperatively stabilized configuration of at least three O-atoms at steps. Here, two O-atoms recruit a third O-atom to a nearby binding site, to produce an active configuration of reactants that is far more reactive. Thus, hydrogen oxidation on Pd reveals a clear example of how reactivity can be enhanced on a working catalyst. We speculate that such active configurations formed by cooperative adsorbate binding play an important role in many real-world catalytic processes.