Microkinetic Modeling
Microkinetic modeling describes a catalytic reaction as a set of elementary steps (adsorption, surface reaction, desorption), each with its own rate constant, usually of Arrhenius form with a pre-exponential factor and an energy barrier. Solving the resulting rate equations for a reactor gives predicted conversions or product flows that can be compared with experiment. Used in reverse, fitting the model to kinetic data measured over a range of temperatures and partial pressures yields estimates of the elementary pre-exponents and barriers, which can then be correlated with catalyst properties such as the d-band center. The approach requires a known mechanism that is simple enough for the parameters to be identifiable from the data.
Simulating TPD with a DFT-informed rate equation (2014)
Simulated TPD spectra for oxygen on Pt(111) were produced by numerically integrating a single elementary-step rate law (second-order associative desorption, pre-exponential factor 3 x 1012 1/(ML s)) with a coverage-dependent barrier whose shape came from DFT, and fitting only two Brønsted-Evans-Polanyi parameters to experiment (Miller et al. 2013). This illustrates using first-principles energetics to constrain the functional form of a kinetic parameter, so that sparse experimental data suffice to determine the remaining constants. Summary: miller2014.
Barriers for H2 adsorption and desorption across CuPd compositions (2015)
Gumuslu and co-workers fit a two-step mechanism for H2-D2 exchange (dissociative adsorption and recombinative desorption on two sites, neglecting isotope effects and coverage dependence) to HD production measured at 100 CuxPd1-x compositions, 14 temperatures and three feed conditions, minimizing the squared conversion error. Pre-exponents were nearly composition independent and consistent with transition state theory, so they were fixed and only the barriers refit. The uncertainty of a fitted barrier also served as a diagnostic: where the desorption barrier’s uncertainty exceeded its value (x > 0.8), the authors concluded the kinetics had become insensitive to desorption, marking a switch from desorption-limited to adsorption-limited exchange near x ≈ 0.8 (Gumuslu et al. 2015). Summary: gumuslu2015; see also High-throughput experimentation.
Microkinetic models under periodic forcing (2025)
Colombo Tedesco and co-workers used rate constants derived from a microkinetic model under an oscillating binding energy (0.1 eV amplitude, 1.4 eV offset, 1000 Hz square wave) for a three-step, two-adsorbate mechanism, and showed that cycle-averaged coverages and limit cycles can be obtained analytically rather than by numerical integration. The analytical result was essentially instantaneous, compared with about 1 s for a boundary value problem solve and about 40 s for forward initial-value integration (Colombo Tedesco et al. 2025). Summary: colombotedesco2025; see also Dynamic catalysis.
An ammonia synthesis volcano from ML-accelerated transition states (2025)
Wander and coworkers reproduced a microkinetic ammonia synthesis volcano on stepped Ru, Fe, Pd, Co, Ni and Rh using an OC20-pretrained EquiformerV2 for intermediate relaxations and N2 dissociation NEBs, with DFT single points for energies. The exhaustive configurational search found systematically lower energy intermediates and transition states than the original study, shifting the volcano and placing Ru more distinctly at the apex, consistent with experiment. The work took about 10 GPU hours, against an estimated 1.7 GPU years for the same NEBs with DFT (Wander et al. 2025). Summary: wander2025a.