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The thesis presented here is focused on two aspects of transition metal mediated catalysis research- one is designing homogeneous rhenium complex with suitable ligand framework for electrochemical reduction of carbon dioxide to address dual issues regarding green house gas removal and hydrocarbon fuel production; another being fabrication of heterogeneous mesoporous manganese oxide to catalyze organic fine chemical synthesis under aerobic atmospheric condition. The quest for conquering fossil fuel energy dependence leads us to develop methodologies for using CO2 as a renewable resource. Electrochemical reduction of CO2 has been considered as a promising procedure for this purpose. Coordination complexes of rhenium and α-diimine ligands are known to resolve the bottleneck of activating the thermally stable and kinetically inert CO2 molecule. In the beginning of the thesis, I have described the development of a new family of α-diimine ligand coordinated rhenium complexes that exhibits remarkable catalytic activity compared to the existing list of analogous systems. The reported compounds in this work consist of three different ligand systems- quinoline, naphthyridine and benzonaphthyridine bound to pyridine or thiazole moieties in the coordination sphere. It has been shown that rate of CO2 reduction and turn over frequency depends significantly on the nature of the ligands. Overall, complexes that have pyridine outperform those having thiazole, with the benzonaphthyridine complexes showing superior activity with rate constant and catalytic turnover of 103 orders. The second part of my thesis describes the design and application of thermally stable and tunable mesoporous manganese oxide to catalyze coupling and aromatization reactions. From the viewpoint of green chemistry, synthesizing valuable organic molecules by using no or minimum additive and maintaining mild reaction condition is of utter importance. We demonstrate synthesis of aromatic nitrogen containing heterocyclic molecules from their non aromatic counterparts by employing robust and inexpensive manganese oxide catalyst in the presence of no other oxidant/additive but air. The same manganese oxide material when fabricated to act as a support for copper oxide catalyst exhibited excellent efficiency for C-O, C-N and C-S bond formation in Ullmann type reaction. Not only the synthetic methodology but the underlying mechanism and role of lattice oxygen present in the structure of catalyst are explained in details following experimental and theoretical studies. The catalytic protocols discussed here have several advantages over the already reported procedures in terms of product separation, reusability of the catalyst, absence of additive, water as by product and air as the terminal oxidant.
Catalysts, heterogeneous, homogeneous, and enzymatic, are comprised of nanometer-sized inorganic and/or organic components. They share molecular factors including charge, coordination, interatomic distance, bonding, and orientation of catalytically active atoms. By controlling the governing catalytic components and molecular factors, catalytic processes of a multichannel and multiproduct nature could be run in all three catalytic platforms to create unique end-products. Unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis. Recyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles - some without homogeneous analogues - for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimize and expand the scope of their reactivity and selectivity. Ongoing efforts are aimed to address the above challenge by heterogenizing homogeneous catalysts, which can be defined as the modification of homogeneous catalysts to render them in a separable (solid) phase from the starting materials and products. Specifically, we grow the small nanoclusters in dendrimers, a class of uniform polymers with the connectivity of fractal trees and generally radial symmetry. Thanks to their dense multivalency, shape persistence and structural uniformity, dendrimers have proven to be versatile scaffolds for the synthesis and stabilization of small nanoclusters. Then these dendrimer-encapsulated metal clusters (DEMCs) are adsorbed onto mesoporous silica. Through this method, we have achieved selective transformations that had been challenging to accomplish in a heterogeneous setting, e.g. [pi]-bond activation and aldol reactions. Extensive investigation into the catalytic systems under reaction conditions allowed us to correlate the structural features (e.g. oxidation states) of the catalysts and their activity. Moreover, we have demonstrated that supported DEMCs are also excellent catalysts for typical heterogeneous reactions, including hydrogenation and alkane isomerization. Critically, these investigations also confirmed that the supported DEMCs are heterogeneous and stable against leaching. Catalysts optimization is achieved through the modulation of various parameters. The clusters are oxidized (e.g., with PhICl2) or reduced (e.g., with H2) in situ. Changing the dendrimer properties (e.g., generation, terminal functional groups) is analogous to ligand modification in homogeneous catalysts, which affect both catalytic activity and selectivity. Similarly, pore size of the support is another factor in determining product distribution. In a flow reactor, the flow rate is adjusted to control the residence time of the starting material and intermediates, and thus the final product selectivity. Our approach to heterogeneous catalysis affords various advantages: (1) the catalyst system can tap into the reactivity typical to homogeneous catalysts, which conventional heterogeneous catalysts could not achieve; (2) unlike most homogeneous catalysts with comparable performance, the heterogenized homogeneous catalysts can be recycled; (3) improved activity or selectivity compared to conventional homogeneous catalysts is possible because of uniquely heterogeneous parameters for optimization. While localized surface plasmon resonance (LSPR) provides a powerful platform for nanoparticle catalysis, our studies suggest that in some cases interband transitions should be considered as an alternative mechanism of light-driven nanoparticle catalysis. The benefits already demonstrated by plasmonic nanostructures as catalysts provided the impetus for examining complementary activation modes based on the metal nanoparticle itself. Leveraging these transitions has the potential to provide a means to highly active catalysis modes that would otherwise be challenging to access. For example, for the preparation of highly active metal catalysts on a subnanosized scale is challenging, thus limiting their exploitation and study in catalysis. Our work suggests a novel and facile strategy for the formation of highly active gold nanocluster catalysts by light illumination of the interband transitions in the presence of the appropriate substrate.
New and Future Developments in Catalysis is a package of seven books that compile the latest ideas concerning alternate and renewable energy sources and the role that catalysis plays in converting new renewable feedstock into biofuels and biochemicals. Both homogeneous and heterogeneous catalysts and catalytic processes will be discussed in a unified and comprehensive approach. There will be extensive cross-referencing within all volumes.The use of catalysts in the nanoscale offers various advantages (increased efficiency and less byproducts), and these are discussed in this volume along with the various catalytic processes using nanoparticles. However, this is not without any risks and the safety aspects and effects on humans and the environment are still unknown. The present data as well as future needs are all part of this volume along with the economics involved. Offers in-depth coverage of all catalytic topics of current interest and outlines future challenges and research areas A clear and visual description of all parameters and conditions, enabling the reader to draw conclusions for a particular case Outlines the catalytic processes applicable to energy generation and design of green processes
The book gives a comprehensive up-to-date summary of the existing information on the structural/electronic properties, chemistry and catalytic properties of vanadium and molybdenum containing catalysts. It discusses the importance of nanoscience for the controlled synthesis of catalysts with functional properties and introduces the necessary background regarding surface properties and preparation techniques, leading from a textbook level to the current state of knowledge. Then follows an extensive survey and analysis of the existing open and patent literature - an essential knowledge source for the development of the new generation of partial oxidation catalysts. Important examples from current research on partial oxidation reactions are reviewed from experts in the field. The next chapter discusses the importance of 2- and 3-dimensional model systems for a fundamental understanding of the structure of transition metal oxide catalysts and its correlation to reactivity. Finally, an outlook on research opportunities within the area of partial oxidation reactions is presented.
This book describes the fundamental concepts, the latest developments and the outlook of the field of nanozymes (i.e., the catalytic nanomaterials with enzymatic characteristics). As one of today’s most exciting fields, nanozyme research lies at the interface of chemistry, biology, materials science and nanotechnology. Each of the book’s six chapters explores advances in nanozymes. Following an introduction to the rise of nanozymes research in the course of research on natural enzymes and artificial enzymes in Chapter 1, Chapters 2 through 5 discuss different nanomaterials used to mimic various natural enzymes, from carbon-based and metal-based nanomaterials to metal oxide-based nanomaterials and other nanomaterials. In each of these chapters, the nanomaterials’ enzyme mimetic activities, catalytic mechanisms and key applications are covered. In closing, Chapter 6 addresses the current challenges and outlines further directions for nanozymes. Presenting extensive information on nanozymes and supplemented with a wealth of color illustrations and tables, the book offers an ideal guide for readers from disparate areas, including analytical chemistry, materials science, nanoscience and nanotechnology, biomedical and clinical engineering, environmental science and engineering, green chemistry, and novel catalysis.
Over the past decade the topic of energy and environment has been ackno- edged among many people as a critical issue to be solved in 21st century since the Kyoto Protocol came into e?ect in 1997. Its political recognition was put forward especially at Heiligendamm in 2007, when the e?ect of carbon dioxide emission and its hazard in global climate were discussed and shared univ- sallyascommonknowledge.Controllingtheglobalwarmingintheeconomical framework of massive development worldwide through this new century is a very challenging problem not only among political, economical, or social c- cles but also among technological or scienti?c communities. As long as the humans depend on the combustion of fossil for energy resources, the waste heat exhaustion and CO emission are inevitable. 2 In order to establish a new era of energy saving and environment benign society, which is supported by technologies and with social consensus, it is important to seek for a framework where new clean energy system is inc- porated as infrastructure for industry and human activities. Such a society strongly needs innovative technologies of least CO emission and e?cient en- 2 ergy conversion and utilization from remaining fossil energies on the Earth. Energy recycling system utilizing natural renewable energies and their c- version to hydrogen may be the most desirable option of future clean energy society. Thus the society should strive to change its energy basis, from foss- consuming energy to clean and recycling energy.
Energy and environment issues are of paramount importance to achieve the sustainable development of our society. Alcohol-fuelled direct oxidation fuel cells (DOFCs), as a clean and highly-efficient energy harvesting engine, have attracted intensive research activity over recent decades. Electrocatalysts are the material at the very heart of the cell that determines the performance of DOFCs. The rapid advances in electrocatalysts, particularly nano-sized ones, have left current information only available in scattered journals. To be truly useful to both present and future researchers, a new book is needed to present an insightful review of the reaction nature of this research and to systematically summarize recent advances in nanocatalysts, and convey a more global perspective. Catalysts for Alcohol-fuelled Direct Oxidation Fuel Cells will present a state-of-the-art review on recent advances in nanocatalysts and electrocatalysis in DOFCs, including both proton and hydroxide ion exchange membrane fuel cells. The main topics covered include a molecular-level understanding of electrocatalysis, the design principles of electrocatalysts, recent advances in nanocatalysts and future perspectives for DOFCs. The book presents a cutting-edge collection on nanocatalysts for alcohol-fuelled direct oxidation fuel cells and brings together the most authoritative researchers in the field from both industry and academia, filling the gap between both sides. Finally, the book will provide an insightful review on electrocatalysis at the molecular- level, which will be useful for postgraduate students and junior researchers in this field. It will be an essential resource for postgraduates, researchers and policy-makers globally in academia, industry, and government institutions.
Highlighting the key aspects and latest advances in the rapidly developing field of molecular catalysis, this book covers new strategies to investigate reaction mechanisms, the enhancement of the catalysts' selectivity and efficiency, as well as the rational design of well-defined molecular catalysts. The interdisciplinary author team with an excellent reputation within the community discusses experimental and theoretical studies, along with examples of improved catalysts, and their application in organic synthesis, biocatalysis, and supported organometallic catalysis. As a result, readers will gain a deeper understanding of the catalytic transformations, allowing them to adapt the knowledge to their own investigations. With its ideal combination of fundamental and applied research, this is an essential reference for researchers and graduate students both in academic institutions and in the chemical industry. With a foreword by Nobel laureate Roald Hoffmann.