Microkinetic Modeling of Nanoparticle Catalysis using Density Functional Theory

Abstract: Heterogeneous catalysis is vitally important to modern society, and one path towardsrational catalyst design is through atomistic scale understanding. The atomistic scalecan be linked to macroscopic observables by microkinetic models based on first-principlescalculations. With the increasing accuracy of first-principles methods and growing com-putational resources, it has become important to investigate and further develop themethodology of microkinetic modeling, which is the theme of this thesis.First, a procedure for mean-field microkinetic modeling of reactions over extended surfacesis developed, where complete methane oxidation over Pd(100) and Pd(111) is studied asan example. The model reveals how the main reaction mechanisms depend on reactionconditions, and shows poisoning as well as promotion phenomena.Second, the effect of entropy in microkinetic modeling is investigated, where CO oxidationover Pt(111) is used as a model reaction. Entropy is found to affect reaction kineticssubstantially. Moreover, a method named Complete Potential Energy Sampling (CPES)is developed as a flexible tool for estimating adsorbate-entropy.Third, a kinetic Monte Carlo method is developed to bridge the materials gap in het-erogeneous catalysis. The computational cost to map out the complete reaction-energy-landscape on a nanoparticle is high, which is solved herein using generalized coordinationnumbers as descriptors for reaction energies. CO oxidation over Pt is studied, andnanoparticles are found to behave differently than the corresponding extended surfaces.Moreover, the active site is found to vary with reaction conditions.Finally, the reaction orders and apparent activation energies are coupled to the microscalevia the degree of rate control, which enhances the atomistic understanding of reactionkinetics.