Catalysis: Volume 27 (Specialist Periodical Reports - Catalysis, Band 27) - Hardcover

Barrientos, Javier; Boutonnet, Magali

Hardcover

ISBN 10: 1782620540 ISBN 13: 9781782620549

Verlag: Royal Society of Chemistry, 2015

Inhaltsangabe

Industrial and academic scientists face increasing challenges to find cost-effective and environmentally sound methods for converting natural resources into fuels, chemicals, and energy. This series provides a balanced and in-depth review of the modern approaches to these challenges, covering major areas such as chemical transformations using two-dimensional hybrid nanocatalysts, catalytic conversion of CO₂ and catalytic oxidation of organic pollutants in aqueous solution using sulfate radicals.

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Industrial and academic scientists face increasing challenges to find cost-effective and environmentally sound methods for converting natural resources into fuels, chemicals and energy. With over 7000 papers published in this field of catalysis each year, keeping up with the literature can be difficult. Catalysis Volume 27 presents critical and comprehensive reviews of the hottest literature published over the last twelve months. Covering major areas such as chemical transformations using two-dimensional hybrid nanocatalysts, conversion of biomass-derived syngas to fuels and catalytic oxidation of organic pollutants in aqueous solution using sulfate radicals, this book is a useful reference for anyone working in catalysis and an essential resource for any library.

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Catalysis Volume 27

By James J. Spivey, Yi-Fan Han, K. M. Dooley

The Royal Society of Chemistry

Copyright © 2015 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-78262-054-9

Contents

Preface, v, 
In situ electron paramagnetic resonance (EPR) – a unique tool for analysing structure and reaction behaviour of paramagnetic sites in model and real catalysts Thomas Risse, Dirk Hollmann and Angelika Brückner, 1, 
Theoretical studies of selective propane oxidation and ammoxidation over vanadium-based multi-metal oxides Vadim V. Guliants, 33, 
Catalytic conversion of biomass-derived synthesis gas to fuels Rodrigo Suárez París, Luis López, Javier Barrientos, Fátima Pardo, Magali Boutonnet and Sven Järås Rodrigo Suárez París, Luis López, Javier Barrientos, Fátima Pardo, Magali Boutonnet and Sven Järås, 62, 
Preparation and catalytic applications of amorphous alloys Hui Li, Wei Wei, Yu Zhao and Hexing Li, 144, 
Present and future prospects in heterogeneous catalysts for C1 chemistry Eunmin Lee, Zhuo Cheng and Cynthia S. Lo, 187, 
Catalytic oxidation of organic pollutants in aqueous solution using sulfate radicals Hongqi Sun and Shaobin Wang, 209, 

CHAPTER 1

In situ electron paramagnetic resonance (EPR) – a unique tool for analysing structure and reaction behaviour of paramagnetic sites in model and real catalysts

Thomas Risse, Dirk Hollmann and Angelika Brückner

DOI: 10.1039/9781782622697-00001

The majority of catalytic reactions involves reduction and/or reoxidation steps in which electrons are transferred between catalysts and substrates. EPR spectroscopy can sensitively probe the local environment of paramagnetic catalytic sites as well as their behavior in catalytic redox processes since it can be applied under a wide range of conditions. After a short summary of the most important application examples of in situ EPR in redox catalysis, the main features of EPR spectra such g and A matrices and approaches of their evaluation are presented using model systems that contain Au atoms deposited on MgO single crystal surfaces. To illustrate the versatility of in situ EPR for deriving structure – reactivity relationships in catalysis, two application examples are presented in more detail: (1) Analysis of heterogeneous supported VOx/TiO2 catalysts during oxidative dehydrogenation of propane in the gas phase and (2) Study of photocatalytic water splitting over a homogeneous catalytic system comprising an iridium photosensitizer complex and an iron carbonyl catalyst.

1 Introduction

EPR spectroscopy has been used to characterize catalysts since very early on, because of its ability to provide detailed information on paramagnetic species such as their geometric and electronic structure or their chemical environment. In terms of the systems being investigated, EPR covers a wide range of applications from heterogeneous, via homogeneous catalysts all the way to enzymatic systems. Paramagnetic species in catalytic systems range from sites considered crucial for catalytic turnover, such as transition metal ions, to paramagnetic reaction intermediates. Analyzing their behavior in situ, i.e. under conditions as close as possible to those of a catalytic reaction, can be most helpful for deriving structure–reactivity relationships and reaction mechanisms. Nevertheless, applications of in situ EPR spectroscopy for monitoring catalytic reactions are not as numerous compared to other common methods such as vibrational spectroscopy or X-ray techniques, due to the fact that it is restricted to systems containing unpaired electrons. However, for catalytic redox processes in which electrons are transferred between catalyst and reactants, in situ EPR (or operando EPR, as it is called when together with the EPR spectrum catalytic conversion/selectivity data are measured) is a unique tool, since it can visualize this electron transfer directly as long as paramagnetic species are involved. This has been illustrated in the past for a variety of hydrocarbon conversion reactions. Thus, mixed oxide and oxynitride bulk phases such as vanadium–phosphorus oxides, vanadium–molybdenum oxides, mixed VTiSbSi oxides, VAlON and VZrON oxynitrides or heteropolyacids of defined structure have been used for selective oxidation of alkanes and aromatics. Such reactions have also been monitored by in situ EPR over supported vanadia and bismuth molybdate catalysts while supported chromia and nickel catalysts were studied during non-oxidative aromatization of alkanes as well as during interaction with butenes. Another important class of heterogeneous catalytic systems analysed by in situ EPR comprises zeolites containing transition metal ions either incorporated in the framework or located in pore positions. Many of such catalysts have been used to remove nitrogen oxides (NOx) from exhaust gases. Relevant examples comprise the use of Co–BEA and Fe–ZSM-5 for selective catalytic reduction of NOx, but also Cu–ZSM-5 has been widely used for the same purpose by Kucherov et al., whose work has been reviewed in ref. 1. The interaction of benzene with oxygen has been recently studied on the same type of catalysts to understand the gas-phase oxidation of benzene to phenol. For a more comprehensive selection of application examples for in situ EPR in heterogeneous catalysis the reader is referred to a number of reviews. Surprisingly, the use of in situ EPR spectroscopy for elucidating structure–reactivity relationships in homogeneous redox catalysis is even more limited than in heterogeneous catalysis.

In EPR spectroscopy the sample is placed in an external magnetic field to lift the degeneracy of the electron spin states and microwave radiation is used to induce magnetic dipole transitions between these states. Historically, most of the information has been obtained using continuous wave EPR spectroscopy operating at a microwave frequency of [approximately equals to]10 GHz in the so-called X-band. Spectrometers of this kind are still by far the most abundant ones, however, the last decades have seen a significant diversification of experimental capabilities, namely, the commercial availability of spectrometers operating at different microwave frequencies as well as pulse spectrometers, which enables the use of these techniques also outside of laboratories dedicated to instrumental developments in EPR spectroscopy.

The aim of this chapter is to acquaint the reader with the basic principles and application opportunities of in situ EPR in redox catalysis. The introductory part starts with a presentation of instrumental aspects and experimental procedures (Section 2), followed by a discussion of the most important parameters, the g and A matrix components, that can be derived from EPR spectra (Section 3). Here we will focus on the examples of Au atoms and O2•- radicals deposited on a MgO(001) surface, which both represent the simplest case of paramagnetic species with a single unpaired electron and a spin of S = 1/2. We will restrict ourselves to the analysis of cw EPR spectra being still the most common ones and typically the initial step in an EPR spectroscopic investigation. This discussion will be amended by only very few examples of pulse EPR techniques (Section 4), which provide valuable additional information on hyperfine interactions in paramagnetic species that...

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 2015
• Sprache: Englisch
• ISBN 10: 1782620540
• ISBN 13: 9781782620549
• Einband: Gebundene Ausgabe
• Anzahl der Seiten: 256
• Herausgeber: Spivey James J., Han Yi-fan, Dooley K. M.
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: Nicht verfügbar