Dissociative chemisorption of H2 on low index and stepped platinum surfaces

Elham Nour Ghassemi
Dissociative chemisorption of H2 on low index and stepped platinum surfaces

Answering the question "how does a molecule react on surface?" is the primary goal in molecule-surface reaction dynamics. When a light molecule like H2 approaches a metal surface, four different processes can take place: diffractive scattering, vibrationally inelastic scattering, rotationally inelastic scattering, and dissociative chemisorption (see also Fig.1).

 

Fig. 1: A schematic illustration of the (A) dissociation, (B1) inelastic vibrational scattering, (B2) inelastic rotational scattering and (B3) diffraction processes accompanying with vibrational excitation of surface atoms (phonon) and electron-hole pair excitation.

 

The above four processes may be accompanied by energy transfer to phonons and/or electron-hole (e-h) pair excitation. It may therefore be necessary to accurately include phonons and electron-hole pair excitation in dynamics simulations of reactive scattering to be capable of predicting molecule-metal surface reactions with chemical accuracy (accuracy 1 kcal/mol or better).

To understand the complex process of the scattering of a molecule from a metal surface one needs to understand simple systems first. The interaction of H2 (the smallest molecule) with a metal surface can serve as a useful model system. In the dissociative chemisorption of H2 on Pt(111), the H2 molecule breaks up in two individual atoms that bind chemically to the surface.  We will investigate whether a Specific Reaction Parameter (SRP) density functional can be developed for the H2 + Pt(111) system, and whether the same functional can then be applied to  H2 reaction on a stepped Pt surface (Pt(533)), a stepped Pt surface poisoned by CO, and a Pt surface with a non-reactive metal alloyed into it. The SRP density functional developed recently by our group for H2 + Cu(111) has allowed a chemically accurate description of a range of experiments on reactive scattering of H2 from Cu(111).

In the present project, we will study the dynamics of H2 dissociation on Pt surfaces by using potential energy surfaces built with SRP-DFT and 6 dimensional quasi-classical and quantum dynamics calculations.

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