Platinum Metals Rev., 2010, 54, (4), 233
“Handbook of Green Chemistry – Green Catalysis”
The first three volumes of the twelve-volume “Handbook of Green Chemistry” focus on “Green Catalysis” and are edited by Professor Robert Crabtree, who is an eminent and important player in the broad area of catalysis, with research interests in organometallic homogeneous catalysis focusing on green chemistry and biomimetics. Robert Crabtree is a Professor of Chemistry at Yale University, USA. He developed a catalyst for homogeneous hydrogenation based on an iridium complex, (1,5-cyclooctadiene)pyridine(tricyclohexylphosphine)iridium(I)hexafluorophosphate, better known as ‘Crabtree's catalyst’ (Figure 1). He has worked in asymmetric synthesis using iridium hydrogenation catalysts, alkane CH activation, the development of dihydrogen complexes, CF activation systems, N-heterocyclic carbenes and has researched into activity in bioinorganic chemistry. He is currently involved in designing and synthesising new homogeneous catalysts, especially chelating carbenes and their iridium complexes. In 2001 he was the winner of the Johnson Matthey Rhodium Bicentenary Competition for a research proposal on the rhodium-based production of aromatic compounds.
Series Editor Paul T. Anastas is known as the “Father of Green Chemistry”. He is a Professor at Yale University and the Director of the Center for Green Chemistry and Green Engineering at Yale. From 2004–2006, Paul Anastas was the Director of the Green Chemistry Institute in Washington, DC. Until June 2004 he served as Assistant Director for Environment at the White House Office of Science and Technology Policy where his responsibilities included a wide range of environmental science issues including furthering international public-private cooperation in areas of science for sustainability such as green chemistry. He developed the twelve principles of green chemistry (1) and has published and edited several books in the field.
This book series from Wiley aims to summarise the significant body of work on green chemistry that has accumulated over the past decade and to detail the breakthroughs, innovation and creativity within green chemistry and engineering. It is aimed at chemists, environmental agencies and chemical engineers wishing to gain an understanding of the world of green chemistry.
Volume 1: Homogeneous Catalysis
Reviewed by Kingsley Cavell
This is a useful and accessible handbook for students and researchers interested in aspects of ‘green chemistry’. ‘Handbook’ is a very apt description for this text as the volume consists of twelve chapters covering a very wide range of topics relevant to green chemistry in homogeneous catalysis. These include the use of green solvents, novel and efficient catalyst systems, immobilised/biphasic catalyst systems and industrial aspects. None of the topics are explored in great detail – to do so would require a full collection of texts rather than the single volume presented here. Instead, each topic is covered in sufficient detail to provide the reader with a flavour of what has been or is being done in each field. References in the various chapters are as recent as 2008 and therefore the literature is reasonably up to date. The various chapters are, in general, written by well-known contributors, all experts in their respective fields. In effect, the book provides a taster of what can be done to improve the efficiency of chemical reactions and to minimise or avoid waste products and contaminants.
The chapters range from short focused ones (15–25 pages in length) highlighting the importance and applicability of the technique or field described, to longer chapters of 30–50 pages with much more detailed description of the chemistry. Appropriately, the book opens with a short introductory chapter discussing the concept of ‘atom economy’, its principles and significance. Most of the platinum group metals, for example, platinum, palladium, rhodium, iridium and ruthenium, play an important role in processes considered as atom efficient. True atom economy is an ideal situation, in that all atoms in the starting materials end up in the desired product(s). In practice this is seldom achieved.
Following this chapter, chapters of various lengths focus on, for example, ‘green’ solvents and immobilised biphasic systems (Chapters 2, 4 to 6), with some industrially relevant sections (Chapters 5 and 7; see for example Schemes I and II) and several specific examples of homogeneous catalysis in green processes (Chapters 3, 11 and 12).
It is a little more difficult to understand why certain of the chapters have been included. For example, Chapter 10 on ‘Palladacycles in Catalysis’ is a good example of efficient homogeneous catalysts, which will be of interest to many, but there are plenty of other examples of efficient catalysed processes in the literature. The relevance to green chemistry of Chapter 9 on ‘Organocatalysis’ is debatable. Such catalytic systems avoid the use of potentially toxic metals, but as the authors themselves acknowledge, the toxicity of many of the organocatalysts is unknown. Furthermore, many metal catalysts operate at very low concentrations, so low that metal residues are generally not an issue, whereas the organocatalysts commonly operate at around 20 mol% and hence can barely be called catalysts at all. While conversions are sometimes good (≥90%), turnover numbers (TONs) and turnover frequencies (TOFs) are poor. However, in support of the chapter's inclusion, this is a relatively new field and improvements and benefits can be expected in the future; in some specialist areas, such as the synthesis of pharmaceuticals, any metal contamination at all can be a problem.
Volume 2: Heterogeneous Catalysis
Reviewed by Stan Golunski
This volume makes interesting reading, but can also be dipped into as an accessible reference source. As an overview of heterogeneous green catalysis – or should that be ‘heterogreeneous catalysis’, as suggested in Chapter 5 – it succeeds on two levels. It summarises the history of this very active field, and maps out the future directions, or at least takes a view on where current pathways are taking us. The twelve chapters cover a broad spectrum of catalytic materials and catalytic processes, starting with the fundamentals of the surface chemistry and chemical engineering of refinery and petrochemical catalysis using zeolites, and finishing with a futuristic process for converting biomass to methane in supercritical water. In between, photocatalysis using titania (TiO2) is the only topic that is accorded the distinction of two chapters of its own. The first of these describes the properties of pure TiO2, followed by a more empirical discussion of the so-called second generation of photocatalysts that are active in visible light, in which metals (such as platinum) or base metal ions are embedded in the oxide; the later chapter provides a similar, but ultimately less optimistic, discussion of the physics and chemistry of dye-sensitised solar cells (Grätzel cells), which consist of a nanoparticulate porous layer of TiO2 onto which ruthenium complexes (the dyes) are absorbed.
The platinum group metals (pgms) are not treated separately, but are referred to throughout most of the volume, as in the chapters on TiO2 mentioned above. Their special role in automotive emissions control is captured in a whistle stop tour (Chapter 9) that begins with the US Clean Air Act of 1970 and ends with the long-anticipated hydrogen economy. Appropriately, it is followed by a chapter on hydrogen production by fuel reforming, in which the pgms feature strongly again. It is interesting that the cited references dry up after 2006, probably reflecting the switchover in global research and development effort from fuel reforming to hydrogen storage that occurred at around that time.
Displacing platinum, palladium and rhodium from their position of strength in emissions control was the probable target for a high-throughput screening campaign described in Chapter 11 (Figure 2). The authors present a persuasive argument for this approach. However, in their flowsheet for catalyst discovery, they have omitted a pre-screening step that is invariably included in industrial research and development, during which any unstable, toxic, regulated or supply-limited elements are eliminated from the screening exercise. While the thrifting and replacement of pgms is a common agenda, their role as a promoter of other catalyst components is becoming increasingly apparent. Chapter 7 provides one such example, by describing how pgm-doping of heteropoly acid catalysts (used industrially for a range of organic transformations) improves their regeneration and so extends their lifetime.
A key feature of green catalysis is that the catalysts themselves have to be green, which means that they need to be manufactured cleanly and sustainably, and to be recycled efficiently. Chapter 2 describes the use of silica-supported sulfonic acids as a green alternative to concentrated sulfuric acid in liquid-phase organic syntheses. In a similar vein, the issues relating to the separation of catalyst and product during homogeneous catalysis can be overcome by designing single-site heterogeneous catalysts in which organometallic complexes are grafted onto a metal oxide support (Chapter 6). This degree of control over the active site is also becoming more prevalent in conventional heterogeneous catalysis (Chapter 4), where our ability to create metal nanoparticles consistently and within a pre-defined size range has led to step-changes in activity and selectivity.
Volume 3: Biocatalysis
Reviewed by David Miller
“Biocatalysis” is the final volume in the “Green Catalysis” series. Hans-Peter Meyer of Lonza AG, a world leading authority on biocatalysis, contributes to a chapter devoted to the use of enzymes for the production of pharmaceuticals (Chapter 7) and this is a good indication of the quality of authorship here.
Given the nature of this Journal I was initially directed to focus my attention on the pgms, but upon leafing through the book it was obvious that this would be an impossible task – only platinum and rhodium get a mention and their appearances are fleeting. Instead it seems sensible to highlight areas of interest for the transition metal enthusiast. Enzymes involved in redox chemistry often use transition metal complexes and so certain chapters do have areas that might be of interest to such a readership.
Chapter 1 is devoted to the heme-containing cytochrome P450 oxidases and there is a useful summary of the current understanding of the catalytic cycle employed by these enzymes. Chapters 5 and 6, on ‘Baeyer-Villiger Monooxygenases in Organic Synthesis’ and ‘Bioreduction by Microorganisms’, respectively, contain only fleeting mentions of transition metals, although a rhodium complex, [Cp(Me)5Rh(bipy)Cl]+ (oxidised form) or [Cp(Me)5 Rh(bipy)H]+ (reduced form), does make an appearance in Chapter 6; it is used to recycle nicotinamide adenine dinucleotide reduced form (NADH) at an electrode surface.
It is in Chapter 8 that this readership will find the most interest. This is devoted to hydrogenases and the hydrogen economy and there is a rich vein of transition metal chemistry found therein. There we meet enzymes that utilise iron-sulfur clusters, nickel-iron and nickel-iron-selenium complexes plus many of the techniques used to study their chemistry such as electron paramagnetic resonance (EPR) and protein film voltammetry. In addition there are a number of synthetic biomimetic metal complexes included. The final chapter is devoted to bioremediation of polyaromatic hydrocarbons and again, despite the importance in this area of iron-containing dioxygenase enzymes, there is little there for the inorganic chemist to get excited about.
Despite the relative lack of interest to the inorganic chemist, as a postgraduate level textbook on biocatalysis it stands up very well – its short length is made up for with extensive and up to date referencing and it includes subjects not covered in competing books, such as the use of enzymes in the unusual solvents supercritical CO2 and ionic liquids. It will certainly be a valuable addition to this reviewer's book collection.
This three-volume set of books covers a wide range of topics within homogeneous, heterogeneous and biocatalysis, with contributions from well-known names in their respective fields. Overall, the books provide an overview of processes and reactions that can be considered ‘green’, with indications of where current directions in research may be going. The role of transition metals including the pgms within this area seems assured.
Future volumes of Wiley's “Handbook of Green Chemistry” will focus on “Green Solvents”, “Green Processes” and “Green Products”. They will appear as three further sets of three volumes each and are expected to be published by 2012 (2).
- P. T. Anastas and J. C. Warner, “Green Chemistry: Theory and Practice”, Oxford University Press, New York, USA, 1998, 30
- Paul T. Anastas Series Editor, Wiley, Handbook of Green Chemistry, 12 volume set, ISBN: 978-3-527-31404-1:http://eu.wiley.com/WileyCDA/WileyTitle/productCd-3527314040,descCd-tableOfContents.html(Accessed on 26th August 2010)
Professor Kingsley Cavell is a Professor of Inorganic Chemistry at Cardiff University and member of staff at the Cardiff Catalysis Institute. He has previously held positions as a Senior Research Scientist at the CSIRO Division of Materials Science, Australia, and as a Guest Professor at RWTH Aachen University, Germany, and Huazhong University, China, among others. His research interests include the design and synthesis of novel ligands for transition metal complexes including platinum and palladium and investigation of the complexes as catalysts in a range of reactions, looking at the effect of ligand bonding and structure on catalytic behaviour.
Professor Stan Golunski is a Deputy Director of the Cardiff Catalysis Institute at Cardiff University. Between 1989 and 2009 he led and managed industrial research projects in catalysis at the Johnson Matthey Technology Centre at Sonning Common, UK, including the industry-university collaboration on Controlling Access of Reactive Molecules to Active Centres (CARMAC). His research interests lie in the field of gas-phase heterogeneous catalysis, particularly for exhaust aftertreatment and hydrogen generation, where pgms are often used.
Dr David Miller is a Research Fellow in Chemical Biology at Cardiff University and an Assistant Director of the Cardiff Catalysis Institute. He has previously completed postdoctoral research at the University of St. Andrews, Birmingham University and Cardiff University. He is particularly interested in the use of synthetic organic chemistry as applied to the solution of biological problems and vice versa. His research uses a combination of chemical synthesis, enzymology and molecular biology to better understand the workings of natural macromolecules.