First-principles Modeling of the Surface Reactivity of Transition Metals with Perturbed Electronic Properties

Abstract

The surface reactivity of transition metals can be varied substantially by introducing perturbations into the electronic system. Previously, the electronic properties of transition metal surfaces have been tailored for improved catalytic performance compared to pure metals. However, the immense phase space of catalytic materials spanned by electronic and structural degrees of freedom precludes thorough screening, even with combinatorial high-throughput experiments or quantum-chemical calculations. The ultimate objective of fundamental research in heterogeneous catalysis is the development of physically transparent, yet sufficiently accurate models for designing catalytic active sites which can perform desired chemical transformations with utmost energy efficiency and minimal environmental impact. The critical question we attempt to answer in this dissertation is: How does a perturbation of surface electronic properties affect the energetics for elementary reaction steps?

To tackle this question, we have developed a general theoretical framework, based on the basic principles of electronic structure theory, providing a fundamental basis for the understanding of variations in the surface reactivity of transition metals with perturbed electronic properties. The implications of the theoretical framework for unravelling the physical factors governing the energetics for elementary reaction steps on metal surfaces and eventually for rational catalyst design are discussed. By utilizing various theoretical tools, mainly Density Functional Theory calculations and Monte Carlo simulations, supported with experimental measurements, we have elaborated the fundamental mechanism of variations in the surface reactivity of transition metals with tailored electronic properties in three different applications: (i) rapid screening of multimetallic electrocatalysts for the oxygen reduction reaction in fuel cells; (ii) understanding of alkali promotion mechanisms for chemical reactions on metal surfaces; (iii) coupling of phonons and energetic electrons for chemical transformations on metallic nanoparticles. Each model system is characterized by one specific type of perturbation introduced by alloying with impurity elements, doping of substrates with chemical promoters, or imposing stimuli for electronic excitations. Many of the concepts developed in these studies can be readily transferable to other types of catalytic materials.