Universiteit Leiden

nl en


Van Marum Colloquium: High precision kinetics of elementary surface reactions: Quantitative comparison of experiment and theory

Wednesday 22 May 2024
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden
Reaction pathways for the rate limiting OH* formation step in the hydrogen oxidation on Pd. Two active sites are required to explain VRK data obtained for: 10−4ML<[O*]< 10−1ML


The kinetics of elementary thermal reactions is fundamental to our understanding of heterogeneous catalysis; however, experimental methods for accurately deriving thermal rate constants are unreliable and theoretical methods for predicting rates remain un-validated. Velocity Resolved Kinetics (VRK) is a new method for obtaining highly accurate kinetics data for surface reactions with excellent signal-to-noise. This new data permits quantitative comparisons between experiment and theory for the first time. In this talk I will present three examples of recent work. Hydrogen atom recombination on Pt surfaces to form gas phase molecular Hydrogen and the catalytic oxidation of hydrogen over Pd to form water. In the first example, we are able to use the principle of detailed balance to predict recombination rate constants from experimentally measured, sticking probabilities. These predictions are in perfect agreement with results obtained from VRK. This example shows us the pitfalls to avoid when applying transition state theory to predict reaction rates on surfaces. One particular important conclusion is that adsorbate spin must be a part of the adsorbate partition function. In a second example, VRK is used to observe formic acid decomposition on reactive metals, which produces reactive two intermediates. These intermediates decompose to CO2 and CO with very different rates. Isotopic labeling results in an observable kinetic isotope effect that can be used to identify the structures of these intermediates experimentally. The observations can also be understood by comparison to theoretically computed reaction pathways. This allows us to confirm the presence of an previously predicted intermediate in the Water Gas Shift Reaction (WGSR). In the third example, I will show the mechanism of the hydrogen oxidation reaction can be elucidated by a fruitful interplay between experiment and theory. This work leads to the insight that cooperative adsorbate binding can produce active configurations that behave like molecules embedded in the surface with their own reactive properties. This work also shows that predictions of Transition State Theory (TST) based on DFT-GGA calculations compare well to experiment, when the correct active configurations are chosen.

This website uses cookies.  More information.