Heterogeneous Catalysts

Advanced Design, Characterization, and Applications, 2 Volumes

Wey Yang Teoh, Atsushi Urakawa, Yun Hau Ng, Patrick Sit

• Publisher: Wiley-VCH
• Year: 2021
• Print ISBN: 9783527344154
• eBook ISBN: 9783527813582
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Presents state-of-the-art knowledge of heterogeneous catalysts including new applications in energy and environmental fields

This book focuses on emerging techniques in heterogeneous catalysis, from new methodology for catalysts design and synthesis, surface studies and operando spectroscopies, ab initio techniques, to critical catalytic systems as relevant to energy and the environment. It provides the vision of addressing the foreseeable knowledge gap unfilled by classical knowledge in the field.

Heterogeneous Catalysts: Advanced Design, Characterization and Applications begins with an overview on the evolution in catalysts synthesis and introduces readers to facets engineering on catalysts; electrochemical synthesis of nanostructured catalytic thin films; and bandgap engineering of semiconductor photocatalysts. Next, it examines how we are gaining a more precise understanding of catalytic events and materials under working conditions. It covers bridging pressure gap in surface catalytic studies; tomography in catalysts design; and resolving catalyst performance at nanoscale via fluorescence microscopy. Quantum approaches to predicting molecular reactions on catalytic surfaces follows that, along with chapters on Density Functional Theory in heterogeneous catalysis; first principles simulation of electrified interfaces in electrochemistry; and high-throughput computational design of novel catalytic materials. The book also discusses embracing the energy and environmental challenges of the 21st century through heterogeneous catalysis and much more.

• Presents recent developments in heterogeneous catalysis with emphasis on new fundamentals and emerging techniques
• Offers a comprehensive look at the important aspects of heterogeneous catalysis
• Provides an applications-oriented, bottoms-up approach to a high-interest subject that plays a vital role in industry and is widely applied in areas related to energy and environment

Heterogeneous Catalysts: Advanced Design, Characterization and Applications is an important book for catalytic chemists, materials scientists, surface chemists, physical chemists, inorganic chemists, chemical engineers, and other professionals working in the chemical industry.

Section II
Surface Studies and Operando Spectroscopies in Heterogeneous Catalysis

12
Toward Precise Understanding of Catalytic Events and Materials Under Working Conditions

Atsushi Urakawa

Delft University of Technology, Department of Chemical Engineering, Catalysis Engineering, Van der Maasweg 9, Delft 2629 HZ, The Netherlands

Heterogeneous catalysis is indispensable for major chemical and energy conversion processes and for environmental protection to improve and sustain the quality of our lives and the environment. Despite the obvious importance, catalysts and catalytic processes are traditionally and even today developed using trial‐and‐error approaches. This is largely due to the intrinsic complexity of heterogeneously catalyzed processes involving various physical and chemical events such as electron transfer, atom motion, atomic and molecular sorption (adsorption and desorption), chemical reaction, molecular diffusion within the pore and outside of catalyst pellets, and fluid dynamics on the pellet to reactor scale (Figure 12.1). These events are taking place on the length scale of picometer to meter (10⁻¹²–10⁰ m) and on the time scale of attoseconds (10⁻¹⁵ seconds, e.g. for electron transfer) up to months and years (e.g. catalyst deactivation). In principle, precise comprehension of catalytic reactions expressed by conversion of reactants and product selectivity requires full understanding of all these events varying in time and length, which seems to be an impossible task.

Figure 12.1 Representative physicochemical events showing the complexity of heterogeneous catalytic processes [1].

The most critical process among the different length scales is that taking place on the atomic scale because this defines the nature of catalysis; in other words, if this molecular‐level catalysis does not work, nothing will happen on other length scales. For this reason, most advances in catalyst characterization are focused on precise understanding of catalytic activity through in‐depth understanding of catalyst materials, active sites, and active species under controlled atmosphere (in situ) and, particularly, under catalysts’ working (operando) conditions [2–4]. The necessity of the latter has been stressed increasingly in the past few decades due to some gaps between the model catalyst and the real‐world catalyst.

Historically, heterogeneous catalysts were widely studied under ultrahigh‐vacuum (UHV) conditions to precisely understand the surface structure and adsorbates over catalyst surfaces by X‐ray photoelectron spectroscopy (XPS), low‐energy electron diffraction (LEED), electron energy loss spectroscopy (EELS), low‐energy electron microscopy (LEEM), and photoemission electron microscopy (PEEM), among other techniques [5, 6]. There were good rationales that these surface‐sensitive techniques had to be carried out under UHV, which evolved from Irving Langmuir’s early experiment on tungsten filament in a vacuum (light) bulb. Firstly, the surface could be cleaned of adsorbed impurities when heated to above Tamman temperature (∼half of melting point) under UHV to minimize the risk of airborne impurities readsorbing onto the surface. Secondly, the analyses of surfaces are best probed by the diffracted or emitted electrons since these low‐energy electrons have extremely short mean free path of less than 2 nm in most solid materials. This means that only electrons from the near surface containing local information of the source environment are able to leave the surface and detected. Thirdly, unlike longer waves such as X‐rays, electrons are easily diffracted and absorbed by any gas molecules en route to the sample (if using electron beam as probing source) or from sample to the detector, which means that the samples and detectors need to be contained in a UHV chamber. Although adsorbate molecules can be introduced into the UHV chamber after surface cleaning, non‐adsorbed or loosely adsorbed molecules would need to be evacuated prior to analyses. For techniques such as LEED, model surfaces of single crystals are required.

Over the last few decades, the precise surface information gained by the advancement of UHV and electron‐probing techniques were formative to the foundation of surface chemistry and heterogeneous catalysis. However, more meticulous information is increasingly being demanded by the field in order to comprehend how active sites and species are formed over technical catalysts or even over model catalyst under efficiently reactive environment that is often under high pressure and temperature. This is because the catalyst structures, especially those on the surface, are dynamic, changing in response to the atmosphere, temperature, and the types and concentration of surface adsorbates. Three gaps, namely, pressure, temperature, and material gaps (Figure 12.2), arise due to such material structures and states uniquely formed under specific operando conditions, and the material gap arises largely due to the complex structure (defective nanostructures and with promoters) of technical catalysts that are often necessary for the catalysts to be highly active [7].

Figure 12.2 Three major ...

Table of contents

• Cover
• Table of Contents
• Title Page
• copyright
• Preface
• Section I: Heterogeneous Catalysts Design and Synthesis
• Section II: Surface Studies and Operando Spectroscopies in Heterogeneous Catalysis
• Section III: Ab Initio Techniques in Heterogeneous Catalysis
• Section IV: Advancement in Energy and Environmental Catalysis
• Index
• End User License Agreement