Modeling and Simulation of Heterogeneous Catalytic Reactions

From the Molecular Process to the Technical System

Olaf Deutschmann

• Publisher: Wiley-VCH
• Year: 2013
• Print ISBN: 9783527321209
• eBook ISBN: 9783527639885
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

The Nobel Prize in Chemistry 2007 awarded to Gerhard Ertl for his groundbreaking studies in surface chemistry highlighted the importance
of heterogeneous catalysis not only for modern chemical industry but also for environmental protection. Heterogeneous catalysis is seen as
one of the key technologies which could solve the challenges associated with the increasing diversification of raw materials and energy sources. It is the decisive step in most chemical industry processes, a major method of reducing pollutant emissions from mobile sources and is present in fuel cells to produce electricity. The increasing power of computers over the last decades has led to modeling and numerical
simulation becoming valuable tools in heterogeneous catalysis.

This book covers many aspects, from the state-of-the-art in modeling and simulations of heterogeneous catalytic reactions on a molecular level to heterogeneous catalytic reactions from an engineering perspective. This first book on the topic conveys expert knowledge from surface
science to both chemists and engineers interested in heterogeneous catalysis. The well-known and international authors comprehensively
present many aspects of the wide bridge between surface science and catalytic technologies, including DFT calculations, reaction dynamics
on surfaces, Monte Carlo simulations, heterogeneous reaction rates, reactions in porous media, electro-catalytic reactions, technical reactors,
and perspectives of chemical and automobile industry on modeling heterogeneous catalysis. The result is a one-stop reference for theoretical
and physical chemists, catalysis researchers, materials scientists, chemical engineers, and chemists in industry who would like to broaden
their horizon and get a substantial overview on the different aspects of modeling and simulation of heterogeneous catalytic reactions.

Chapter 1

Modeling Catalytic Reactions on Surfaces with Density Functional Theory

John A. Keith, Josef Anton, Payam Kaghazchi, and Timo Jacob

1.1 Introduction

Predicting the reactivity of catalytic systems is a nontrivial process that usually requires knowledge about its geometric and electronic structure, properties determined by quantum mechanics (QM). Solving the Schrödinger equation¹ is a nontrivial task even for small systems, and it becomes especially arduous when the system involves multiple phases as is the case in a surface reaction. Theoretical calculations nevertheless provide useful and important perspectives on chemical reactions that are not accessible through experimental observations alone. Figure 1.1 schematically shows the hierarchy of multiscale modeling, starting from the subatomic regime, over the electronic and atomistic regimes, to the meso- and finally the macroscale. Different theoretical methods have been established to address questions related to each regime (or timescale and length scale); however, realistic processes usually involve effects from all scales. In this chapter, we will focus on the electronic and atomistic regimes, which not only provide the basis for climbing up the hierarchy of multiscale modeling but also provide important mechanistic information on catalytic reactions.

Figure 1.1 Hierarchy of multiscale modeling of different time and length regimes.

Quantum chemistry is the application of QM to better understand chemical systems. In its purest form, QM calculations solve the Schrödinger equation, which provides the energy of a given configuration of nuclei and their electrons. There are two general approaches to do this. One way is to solve the energy given by the Schrödinger equation approximately using a nonclassical wavefunction. Another popular approach, density functional theory (DFT), uses the electronic density to evaluate the energy of a system via an approximate functional. Both approaches have their merits and provide a nonthermodynamical representation of the energy of a system of electrons.

This chapter gives an introductory overview of the essential concepts behind theoretical calculations of surface reactions, which we then apply to better understand one of the key features in energy conversion and fuel cell technology: the electrocatalytic oxygen reduction reaction (ORR). After describing the multibody problem in quantum mechanics, we will discuss the fundamentals behind wave function- and density-based methods used to solve this problem. We will then focus on density functional theory and its advantages and disadvantages in applications to catalysis. Section 1.2, the first part of this chapter, ends with brief technical details one has to grapple with when modeling surface reactions. This includes thermodynamic approximations and other considerations that extend calculated values from theoretical studies to be more comparable to experiment. Section 1.3, the second part of this chapter, shows an example how quantum mechanical DFT calculations can resolve mechanistic details of a rather complex surface reaction.

1.2 Theoretical Background

1.2.1 The Many-Body Problem

Many material properties of interest to physicists and chemists can be obtained by solving the many-body Schrödinger equation. In stationary, nonrelativistic terms it can be written as

(1.1)

where

is the Hamilton operator,

is the many-body wave function,

is the total energy of the system,

is the spin coordinate of electron

, and finally

and

are the spatial coordinates of electron i and nucleus

, respectively. The Hamiltonian for a system consisting of a set of nuclei and electrons ca...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• Preface
• List of Contributors
• Chapter 1: Modeling Catalytic Reactions on Surfaces with Density Functional Theory
• Chapter 2: Dynamics of Reactions at Surfaces
• Chapter 3: First-Principles Kinetic Monte Carlo Simulations for Heterogeneous Catalysis: Concepts, Status, and Frontiers
• Chapter 4: Modeling the Rate of Heterogeneous Reactions
• Chapter 5: Modeling Reactions in Porous Media
• Chapter 6: Modeling Porous Media Transport, Heterogeneous Thermal Chemistry, and Electrochemical Charge Transfer
• Chapter 7: Evaluation of Models for Heterogeneous Catalysis
• Chapter 8: Computational Fluid Dynamics of Catalytic Reactors
• Chapter 9: Perspective of Industry on Modeling Catalysis
• Chapter 10: Perspectives of the Automotive Industry on the Modeling of Exhaust Gas Aftertreatment Catalysts
• Index