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

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.