Download or read book Mechanistic Understanding and Improvement of Photochemical Proton Reduction Catalyzed by Iron Carbonyl Complexes for Sustainable Hydrogen Production written by Steffen Fischer and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Mechanistic investigation of three homogeneous, photochemical proton reduction systems that comprise Ir or Cu based photosensitizers and iron carbonyl catalysts to produce hydrogen. Operando IR spectroscopy coupled with gas volumetry was applied supported by other spectroscopic techniques. The rate determining steps, deactivation mechanisms and catalytic key species were determined, with the latter being a self-assembling [FeFe]-hydrogenase mimic in case phosphines are present as co-catalysts in the reaction mixture. These results lead to a better understanding and improvement of the systems.eng

Download or read book Mechanistic Details for Cobalt Catalyzed Photochemical Hydrogen Production in Aqueous Solution written by and published by . This book was released on 2013 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of sunlight to drive chemical reactions that lead to the reduction of water to produce hydrogen is a potential avenue of solar energy utilization. There are many individual steps that take place in this process. This paper reports the investigation of a particular system that involves light absorbing molecules, electron donating agents and a catalyst for water reduction to hydrogen. We evaluated the efficiency of the light induced formation of a strong electron donor, the use of this donor to reduce the catalyst and finally the efficiency of the catalyst to produce hydrogen from water. From this, the sources of loss of efficiency could be clearly identified and used in the design of better systems to produce hydrogen from water.

Download or read book Combined Theoretical and Experimental Investigation of Hydrogen Production Catalysis written by and published by . This book was released on 2018 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: The widespread use of solar energy has been limited in part by the issue of effective storage. Water splitting is a means of converting solar energy into chemical fuel, in the form of hydrogen gas. It can be performed through both photochemical and electrochemical processes, via the two half reactions of water oxidation and proton reduction. Electrochemically, the catalyst receives electrons from an external circuit, which can be coupled to a renewable source such as a solar cell. Photochemically, a light-absorbing molecule provides an excited electron to a catalyst, which either generates oxygen or hydrogen gas. The work described herein studies both photochemical and electrochemical proton reduction using two different systems made of inexpensive transition metal and organic components. Nickel pyridine 2-thiolate (Ni(PyS)3-) (PyS=pyridinthiolate) has been demonstrated to have good stability and activity as a proton reduction catalyst. It is applied here as an electrocatalyst, due to the wealth of mechanistic information that can be obtained through electrochemical experiments. Six derivatives of Ni(PyS)3- were synthesized through uniform ligand modification to all three PyS- ligands using a series of electron rich or poor substituents. The physical properties of interest were investigated experimentally through electrochemical methods and UV-vis absorbance spectroscopy. Specifically, the desired properties for a hydrogen production catalyst are high proton affinity, quantified through the pKa, and low overpotential, quantified through E0. Each compound was also studied in depth using computational modeling of the various possible catalytic pathways. By combining the results of computational study with experimental results, mechanistic insight could be gained. The same joint theoretical and experimental methodology has been used to study the effect of non-uniform ligand modification. Four heteroleptic compounds were selected for study, two containing electron poor ligands and two containing electron rich ligands in varied ratios. What is found is that not only do the electronics of each ligand influence physical properties, but the placement of each ligand matters as well. Finally, photochemical hydrogen production was performed using polyvinylpyrrolidone (PVP)-coated carbon quantum dots (CQDs) as a photosensitizer, and nickel nanoparticles (NiNPs) as a catalyst. Total hydrogen production by CQD/NiNP composites as a function of the amount of PVP coating was investigated as well as various mechanistic and photophysical properties.

Download or read book Photochemical Charge Transfer in Nanostructured Photocatalysts for Solar Hydrogen Production written by Jiarui Wang and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Solar energy is a promising sustainable energy source to reduce greenhouse gas emission from combustion of fossil fuels and slow down the global climate change. Solar hydrogen generation via photocatalytic water splitting is potentially the most cost-effective way to produce solar fuels, so the development of efficient photocatalysts is one of the most important targets for scientific research. However, the application of inorganic materials for solar water splitting is currently limited by our understanding of photochemical charge transfer on the nanoscale, where space charge layers are less effective for carrier separation. Therefore, this dissertation focuses on the preparation of well-defined photocatalysts for the water splitting reaction and on the characterization of photochemical charge transfer on their interfaces. This will be accomplished through the application of surface photovoltage and photoelectrochemical measurements, and with photocatalytic reactivity tests. Results from this study can guide the design of inorganic photocatalysts with improved efficiency for solar energy conversion into fuel. Chapter 2 describes surface photovoltage spectroscopy studies to measure the internal photovoltages in a hydrogen evolution photocatalyst, single crystalline platinum/ruthenium-modified Rh-doped SrTiO3 nanocrystals. Voltages of -0.88 V and -1.13 V are found between the light absorber and the Ru and Pt cocatalysts, respectively, and a voltage of -1.48 V for a Rh-doped SrTiO3 film on an Au substrate. The voltages shows that the Pt and Ru cocatalysts not only improve the redox kinetics but also aid charge separation in the absorber. The voltages with redox agents correlate well with the photocatalytic performance of the catalyst and are influenced by the built-in potentials of the donor-acceptor configurations, the physical separation of donors and acceptors, and the reversibility of the redox reaction. The photovoltage data also allow the identification of a photosynthetic system for hydrogen evolution (80 [mu]mol·g−11h−1) under visible light illumination (>400 nm) from 0.05 M aqueous K4[Fe(CN)6]. Chapter 3 shows that suspended p-Si nanowires obtained by etching of an Al-doped silicon wafer facilitate photochemical hydrogen evolution under visible light. The activity varies greatly between sacrificial donors and can be increased by attachment of MoS2 cocatalysts, which promote proton reduction and charge transfer at the silicon-MoS2 interface. Overall, the activity of suspended p-Si nanorods is limited by the stability of the material in neutral solutions. A basic or neutral environment with photo-excitation can lead to silicon corrosion. In 0.05 M ferrocyanide at pH 6.5, the hydrogen evolution rate for SiNW/MoS2 was as high as 106 [mu]mol (10mg)−1 h−1 accompanied by silicon corrosion. The rate without corrosion decreased to 0.64 [mu]mol (10mg)−1 h−1 at a lower pH of 4.7. With silicon corrosion, the rate also reached 117 [mu]mol (10mg)−1 h−1 in pH 6.5 0.05 M Na2SO3 solution and 678 [mu]mol (10mg)−1 h−1 in 0.1 M NaSH without pH control. Silicon corrosion was not found in formaldehyde and methanol solutions, but the rates of SiNW/MoS2 and SiNW were as low as 0.40 and 0.18 [mu]mol (10mg)−1 h−1 for methanol solution, and 0.71 and 0.27 [mu]mol (10mg)−1 h−1 for formaldehyde solution. The increased hydrogen evolution with silicon corrosion can be attributed to both electron donating of silicon and reduced charge transfer resistivity with the dissolution of surface oxide layer on silicon nanowires. These findings can improve the understanding of photochemistry of Si-MoS2 catalyst, and help avoiding silicon corrosion in photocatalysis.

Download or read book Mechanistic Studies of Hydrogen Evolution in Aqueous Solution Catalyzed by a Tertpyridine amine Cobalt Complex written by and published by . This book was released on 2015 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Iron Complexes for Photocatalytic Hydrogen Generation written by Carolyn L. Hartley and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasing global energy demands have led to renewed interest in alternative energy sources such as solar power. Devices designed to harness solar power and convert absorbed energy into hydrogen fuel are an attractive option (termed ‘artificial photosynthesis’), and require the development of catalysts for hydrogen generation. We report here a family of iron complexes that are active catalysts for proton reduction to generate H2 gas. Photochemical studies show that ligand modification of the complexes significantly impacts activity levels, and quenching studies elucidate mechanism. These complexes present active, stable, and cost-effective means for hydrogen generation in devices for artificial photosynthesis.

Download or read book Mechanism Based Design of Green Oxidation Catalysts written by and published by . This book was released on 2015 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: In modern era of scarce resources, developing chemical processes that can eventually generate useful materials and fuels from readily available, simple, cheap, renewable starting materials is of paramount importance. Small molecules, such as dioxygen, dinitrogen, water, or carbon dioxide, can be viewed as ideal sources of oxygen, nitrogen, or carbon atoms in synthetic applications. Living organisms perfected the art of utilizing small molecules in biosynthesis and in generating energy; photosynthesis, which couples carbohydrate synthesis from carbon dioxide with photocatalytic water splitting, is but one impressive example of possible catalytic processes. Small molecule activation in synthetic systems remains challenging, and current efforts are focused on developing catalytic reactions that can convert small molecules into useful building blocks for generating more complicated organic molecules, including fuels. Modeling nature is attractive in many respects, including the possibility to use non-toxic, earth-abundant metals in catalysis. Specific systems investigated in our work include biomimetic catalytic oxidations with dioxygen, hydrogen peroxide, and related oxygen atom donors. More recently, a new direction was been also pursued in the group, fixation of carbon dioxide with transition metal complexes. Mechanistic understanding of biomimetic metal-catalyzed oxidations is critical for the design of functional models of metalloenzymes, and ultimately for the rational synthesis of useful, selective and efficient oxidation catalysts utilizing dioxygen and hydrogen peroxide as terminal oxidants. All iron oxidases and oxygenases (both mononuclear and dinuclear) utilize metal-centered intermediates as reactive species in selective substrate oxidation. In contrast, free radical pathways (Fenton chemistry) are common for traditional inorganic iron compounds, producing hydroxyl radicals as very active, non-selective oxidants. Recent developments, however, changed this situation. Growing families of synthetic iron complexes that resemble active sites of metalloenzymes produce metal-based intermediates (rather than hydroxyl radicals) in reactions with oxygen donors. These complexes are very promising for selective oxygen and peroxide activation. In order to understand the mechanisms of metal-based small molecule activation, kinetically competent metal-oxygen intermediates must be identified. One of the grand challenges identified by the Department of Energy workshop "Catalysis for Energy" is understanding mechanisms and dynamics of catalyzed reactions. The research summarized herein focuses on detailed characterization of the formation and reactivity of various iron-peroxo- and iron-oxo intermediates that are involved in catalysis. Rates of rapid reactions were studied at low temperatures by a specialized technique termed cryogenic stopped-flow spectrophotometry. These measurements identified reaction conditions which favor the formation of catalytically competent oxidants. Chemical structures of reactive complexes was determined, and new, efficient catalysts for hydrocarbon oxidation were synthesized. Importantly, these catalysts are selective, they promote oxidation of hydrocarbons at a specific site. The catalysts are also efficient and robust, hundreds of cycles of substrate oxidation occur within minutes at room temperature. Furthermore, they enable utilization of environmentally friendly oxidants, such as hydrogen peroxide, which produces water as the only byproduct. Mechanistic insights uncovered the role of various acid-containing additives in catalytic oxidations. Proton delivery to the active catalytic sites facilitated oxidations, similarly to the catalytic pathways in metal-containing enzymes. Under certain conditions, two metals in one complex can act in concert, modeling the reactivity of a bacterial enzyme which converts methane into methanol. In related studies, a family of nickel complexes that react with carbon ...

Download or read book Metal Organic Framework Composites written by Anish Khan and published by Materials Research Forum LLC. This book was released on 2019-10-25 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: Because of their nanoporous structures and ultra-high surface areas Metal-Organic Framework Composites (MOFs) are very interesting materials. The book focusses on the following applications: gas capture and storage, especially molecular hydrogen storage; performance enhancement of Li-ion batteries; gas separation, nano-filtration, ionic sieving, water treatment, and catalysis; sustainable renewable energy resources, electrochemical capacitors, including supercapacitors, asymmetric supercapacitors and hybrid supercapacitors; biomedical disciplines including drug delivery, theranostics; biological detection and imaging; nanoparticle photosensitizers for photodynamic therapy (PDT) and photothermal therapy (PTT). Keywords: MOF Materials, Hydrogen Storage, Renewable Energy Applications, Lithium Batteries, MOF-Quantum Dots, Clean Energy, Nanoporous MOFs, Supercapacitors, Therapeutic Applications, Biosensing, Bioimaging, Phototherapy of Cancer, Gas Separation, Nano-filtration, Ionic Sieving, Water Treatment, Drug Delivery, Theranostics; Nanoparticle Photosensitizers, Photodynamic Therapy (PDT), Photothermal Therapy (PTT).

Download or read book Olefin Polymerization written by Walter Kaminsky and published by Wiley-VCH. This book was released on 2006-08-18 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: With an enormous velocity, olefin polymerization has expanded to one of the most significant fields in polymers since the first industrial use about 50 years ago. In 2005, 100 million tons of polyolefins were produced - the biggest part was catalyzed by metallorganic compounds. The Hamburg Macromolecular Symposium 2005 with the title "Olefin Polymerization" involved topics such as new catalysts and cocatalysts, kinetics, mechanism and polymer reaction engineering, synthesis of special polymers, and characterization of polyolefins. The conference combined scientists from different disciplines to discuss latest research results of polymers and to offer each other the possibility of cooperation. This is reflected in this volume, which contains invited lectures and selected posters presented at the symposium.

Download or read book Photophysics Photochemical and Substitution Reactions written by Satyen Saha and published by BoD – Books on Demand. This book was released on 2021-06-30 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book represents a unique blend of topics covering photon-initiated reactions to substitution reactions. Additionally, several fantastic chapters on the photophysics of popular dyes and their applications make the book interesting for researchers working on photon-initiated physical and chemical processes.

Download or read book Iron Porphyrins written by A. B. P. Lever and published by Wiley-VCH. This book was released on 1989-03-31 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: Porphyrins play a vital role in many biological functions including oxygen transport, electron transfer and catalyzing the incorporation of oxygen into other molecules. This current survey discusses the use of modern physical techniques to probe porphyrin structure and function. The authors review the data available through a particular technique and show what can be learned therefrom about the (electronic) structure and function of biologically important porphyrins. The techniques include magnetic circular dichroism, X-ray absorption fine structure (EXAFS) and Mössbauer spectroscopies. All contributors are well known in their respective fields, enjoying world-wide reputation.

Download or read book Visible Light Photocatalysis in Organic Chemistry written by Corey R.J. Stephenson and published by John Wiley & Sons. This book was released on 2018-05-29 with total page 454 pages. Available in PDF, EPUB and Kindle. Book excerpt: Filling the need for a ready reference that reflects the vast developments in this field, this book presents everything from fundamentals, applications, various reaction types, and technical applications. Edited by rising stars in the scientific community, the text focuses solely on visible light photocatalysis in the context of organic chemistry. This primarily entails photoinduced electron transfer and energy transfer chemistry sensitized by polypyridyl complexes, yet also includes the use of organic dyes and heterogeneous catalysts. A valuable resource to the synthetic organic community, polymer and medicinal chemists, as well as industry professionals.

Download or read book Iron Catalysis in Organic Chemistry written by Bernd Plietker and published by John Wiley & Sons. This book was released on 2008-09-08 with total page 295 pages. Available in PDF, EPUB and Kindle. Book excerpt: This first comprehensive book to cover this exciting field also deals with the biological aspects, such as enzymes with iron. Following an introduction, this handy reference and handbook goes on to deal with reductions, oxidations of C, H- and C=C bonds, oxidative allylic oxygenation and amination, the oxidation of heteroatoms, cross coupling reactions, aromatic and nucleophilic substitutions, addition to carbonyl compounds, and cyclisations as well as ring opening reactions. The chapters are clearly classified according to the reaction type, allowing readers to quickly locate the desired information.

Download or read book Non Noble Metal Catalysis written by Robertus J. M. Klein Gebbink and published by John Wiley & Sons. This book was released on 2019-04-29 with total page 610 pages. Available in PDF, EPUB and Kindle. Book excerpt: An expert overview of current research, applications, and economic and environmental advantages The study and development of new homogeneous catalysts based on first-row metals (Mn, Fe, Co, Ni, and Cu) has grown significantly due to the economic and environmental advantages that non-noble metals present. Base metals offer reduced cost, greater supply, and lower toxicity levels than noble metals?enabling greater opportunity for scientific investigation and increased development of practical applications. Non-Noble Metal Catalysis provides an authoritative survey of the field, from fundamental concepts and computational methods to industrial applications and reaction classes. Recognized experts in organometallic chemistry and homogeneous catalysis, the authors present a comprehensive overview of the conceptual and practical aspects of non-noble metal catalysts. Examination of topics including non-innocent ligands, proton-coupled electron transfer, and multi-nuclear complexes provide essential background information, while areas such as kinetic lability and lifetimes of intermediates reflect current research and shifting trends in the field. This timely book demonstrates the efficacy of base metal catalysts in the pharmaceutical, fine-chemical, and agrochemical industries, addressing both environmental and economic concerns. Providing essential conceptual and practical exploration, this valuable resource: -Illustrates how unravelling new reactivity patterns can lead to new catalysts and new applications -Highlights the multiple advantages of using non-noble metals in homogenous catalysis -Demonstrates how the availability of non-noble metal catalysis reduces costs and leads to immense savings for the chemical industry -Reveals how non-noble metal catalysis are more sustainable than noble metals such as palladium or platinum Non-Noble Metal Catalysis: Molecular Approaches and Reactions is an indispensable source of up-to-date information for catalytic chemists, organic chemists, industrial chemists, organometallic chemists, and those seeking to broaden their knowledge of catalytic chemistry.

Download or read book Iron Catalysis written by Bernd Plietker and published by Springer Science & Business Media. This book was released on 2011-01-05 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: Juan I. Padrón and Víctor S. Martín: Catalysis by means of Fe-based Lewis acids; Hiroshi Nakazawa*, Masumi Itazaki: Fe–H Complexes in Catalysis; Kristin Schröder, Kathrin Junge, Bianca Bitterlich, and Matthias Beller: Fe-catalyzed Oxidation Reactions of Olefins, Alkanes and Alcohols: Involvement of Oxo- and Peroxo Complexes; Chi-Ming Che, Cong-Ying Zhou, Ella Lai-Ming Wong: Catalysis by Fe=X Complexes (X=NR, CR2); René Peters, Daniel F. Fischer and Sascha Jautze: Ferrocene and Half Sandwich Complexes as Catalysts with Iron Participation; Markus Jegelka, Bernd Plietker: Catalysis by Means of Complex Ferrates.

Download or read book Homogeneous Photocatalysis written by M. Chanon and published by John Wiley & Sons. This book was released on 1997-03-06 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photocatalysis and related processes occupy a strategic position for the future of photochemistry. This volume provides an introduction to basic concepts and explains how applications work at the molecular level.

Download or read book CO2 Hydrogenation Catalysis written by Yuichiro Himeda and published by John Wiley & Sons. This book was released on 2021-06-28 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: A guide to the effective catalysts and latest advances in CO2 conversion in chemicals and fuels Carbon dioxide hydrogenation is one of the most promising and economic techniques to utilize CO2 emissions to produce value-added chemicals. With contributions from an international team of experts on the topic, CO2 Hydrogenation Catalysis offers a comprehensive review of the most recent developments in the catalytic hydrogenation of carbon dioxide to formic acid/formate, methanol, methane, and C2+ products. The book explores the electroreduction of carbon dioxide and contains an overview on hydrogen production from formic acid and methanol. With a practical review of the advances and challenges in future CO2 hydrogenation research, the book provides an important guide for researchers in academia and industry working in the field of catalysis, organometallic chemistry, green and sustainable chemistry, as well as energy conversion and storage. This important book: Offers a unique review of effective catalysts and the latest advances in CO2 conversion Explores how to utilize CO2 emissions to produce value-added chemicals and fuels such as methanol, olefins, gasoline, aromatics Includes the latest research in homogeneous and heterogeneous catalysis as well as electrocatalysis Highlights advances and challenges for future investigation Written for chemists, catalytic chemists, electrochemists, chemists in industry, and chemical engineers, CO2 Hydrogenation Catalysis offers a comprehensive resource to understanding how CO2 emissions can create value-added chemicals.