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Sabatier Principle

The foundation of activity scoring in ASCICat.

Historical Background

Paul Sabatier (Nobel Prize 1912) proposed:

"An ideal catalyst binds reaction intermediates with intermediate strength."

Too weak binding → reactants don't stick Too strong binding → products don't desorb

The Volcano Plot

Plotting catalytic activity vs. binding energy produces a "volcano":

Activity
   ↑
   |           ★ Optimum
   |          /|\
   |         / | \
   |        /  |  \
   |    Pt /   |   \ Au
   |      /    |    \
   | Ni  /     |     \ Ag
   |____/______|______\____→ Binding Energy
    strong    optimal    weak

Theoretical Basis

Brønsted-Evans-Polanyi (BEP) Relations

Activation energy correlates with reaction energy:

\[E_a = E_a^0 + \alpha \Delta E\]
  • Stronger binding → Lower adsorption barrier
  • Stronger binding → Higher desorption barrier

Scaling Relations

Different intermediates scale together:

\[\Delta E_{*OH} = a \cdot \Delta E_{*O} + b\]

This enables single-descriptor screening.

Application to HER

For Hydrogen Evolution Reaction:

\[\Delta E_{opt} = -0.27 \text{ eV}\]

Derivation:

  1. Thermoneutral point: \(\Delta G_{H*} \approx 0\)
  2. ZPE and entropy corrections: \(\Delta E_{H*} \approx -0.27\) eV
  3. Validated by Pt(111) experiments

Application to CO2RR

Pathway Intermediate \(\Delta E_{opt}\)
CO *CO -0.67 eV
CHO *CHO -0.48 eV
COCOH *COOH -0.32 eV

Linear Scoring Implementation

\[S_a = \max\left(0, 1 - \frac{|\Delta E - \Delta E_{opt}|}{\sigma_a}\right)\]

Parameters:

  • \(\Delta E_{opt}\) = Volcano peak position
  • \(\sigma_a\) = Width parameter (typically 0.15 eV)

Why 0.15 eV?

The width parameter accounts for:

  1. DFT uncertainty (~0.1 eV)
  2. Functional variation (~0.05-0.1 eV)
  3. Surface coverage effects

References

  • Sabatier, P. Ber. Dtsch. Chem. Ges. 44, 1984 (1911)
  • Nørskov, J. K. et al. J. Catal. 209, 275 (2002)
  • Greeley, J. et al. Nat. Mater. 5, 909 (2006)