(168f) First-Principles Modeling of Hot Electron Assisted Chemical Bond Activation On Metal Surfaces | AIChE

(168f) First-Principles Modeling of Hot Electron Assisted Chemical Bond Activation On Metal Surfaces

Authors 

Xin, H. - Presenter, University of Michigan
Linic, S., University of Michigan-Ann Arbor



Chemical reactions on metal surfaces are typically driven by phonons, i.e., vibrational excitation of adsorbed molecules by thermal energies. Interestingly, it is well-established in the field of femtochemistry that energetic electrons, generated from optical excitation of metal single crystals with ultrashort laser pulses or other sources, can also be exploited to drive surface chemical reactions, often through novel reaction channels not accessible in thermal reactions. Recently, we showed that plasmonic nanostructures of coinage metals effectively couple thermal and low-intensity photonic stimuli to drive chemical transformations. Intensity- and wavelength-dependence of steady-state reaction rates together with kinetic isotope experiments suggest that this process is electron-driven in nature, attributed to the excitation of localized surface plasmon resonance (LSPR).

In this talk we will discuss our approach to study direct photocatalytic reactions on plasmonic nanostructures from first-principles. Photocatalytic ethylene epoxidation (catalyzed by silver (Ag) cubes) was used as the test reaction, where the O2 dissociation is the rate-limiting step. We present a model that allows us to evaluate within a non-adiabatic dynamics the coupling of vibrational excitations of adsorbed O2* and energetic electrons from the Landau damping of LSPR while the adsorbate-surface interaction is described by ab-initio potential energy surfaces (PESs). We used DFT calculations for the PES of O2 dissociation on Ag(100) in its neutral state, while ΔSCF-DFT calculations were used to for the PES of the TNI state. The probability that an energetic electron with a particular energy scatters into the 2pi* anti-bonding orbital of O2 gaining a given amount of vibrational energy is computed using the Green’s function with the Newns-Anderson-type Hamiltonian. This Hamiltonian includes a non-adiabatic coupling of the energetic electron to adsorbate reaction coordinate. We substantiate that important aspects of the reaction dynamics are well captured by the model. In addition, we will also discuss electronic factors governing vibrational excitations of adsorbed species on metal surfaces and provides the rationale for manipulation of metal surfaces for electron-assisted surface reactions.

  1. P. Christopher, H. Xin, S. Linic, Nature Chem., 3, 467, (2011)
  2. P. Christopher, H. Xin, A. Marimuthu, S. Linic, Nature Mater. 11, 1044, (2012)
  3. S. Linic, P. Christopher, H. Xin, A. Marimuthu, Acc. Chem. Res., accepted (2013)