Uncertainty Quantification of a Theoretical Study of the (reverse) Water-Gas Shift Reaction over Pt (111)

Uncertainty quantification of a theoretical study of the (reverse) water-gas shift reaction over Pt (111)

Donald Mitchell

The City College of New York

 

Advisors: Eric Walker, Dr. Andreas Heyden

The water-gas-shift (WGS), CO + H₂O ↔ CO₂ + H₂ , and its reverse reaction are key processes in the purification of hydrogen, synthesis of methanol and production of long chain hydrocarbons.  In this work density functional theory is employed to study the reverse and forward water-gas shift reaction on a Pt(111) catalyst.  A Pt catalyst was modeled as a four-layer slab with a 4x3 surface unit cell using the VASP software with Perdew, Burke, Ernzerhof functional.  Transition state searches for surface reactions were conducted with nudged elastic band and dimer methods.  A microkinetic model was developed to generate model turnover frequencies at relevant temperature and pressure conditions.  Elementary reaction rate constants of the microkinetic model were computed using harmonic transition state theory.  Model turnover frequency results are compared to experiments at a variety of conditions.  The model qualitatively agrees with experiments although the model consistently underestimates the experiments.  Finally, due to the inexact nature of density functional theory and the stiff equations in the microkinetic model, uncertainty quantification is necessary to report reliable turnover frequency results.  Therefore, uncertainty quantification is displayed for selected model results.  Future work to improve the model includes adding lateral interaction effects to binding energies of molecules adsorbed to the catalyst.