Electronic Excitations in Thermal Heterogeneous Catalysis

Most studies of thermal catalysis assume that the system remains in the electronic ground state. However, electronic excitations are easily induced in metal surfaces, due to the lack of a band gap. Here, we show that processes on catalytic surfaces can induce electronic excitations, and we examine the possible effects of these processes on surface chemistry.

We performed nonadiabatic dynamics using real-time, time-dependent density functional theory, propagating the nuclei using Ehrenfest dynamics. We study several trajectories of an N₂ molecule interacting with Ru nanoparticles ranging in size from 13 to 147 atoms. These simulations show that, during the adsorption and dissociation processes, a significant amount of energy can be dissipated into electronic degrees of freedom, comparable to the amount of energy dissociated into ionic vibrations. This suggests that the electronic structure of catalytic surfaces may, transiently, be quite different from the ground state. We characterize the electronic structure and spatial character of the excitations, and we examine how they can affect the surface chemistry of other species reacting on the nanoparticle.