Photopromoted Reactions of Carbon Dioxide with Hydrogen Over Transition-metal Oxide Catalysts PDF Download

Author: Bruno Ignacio Rubio
Publisher:
ISBN:
Category : Carbon dioxide
Languages : en
Pages : 456

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Author: Arno Behr
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 180

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Author: M. Aresta
Publisher: Springer Science & Business Media
ISBN: 9400906633
Category : Science
Languages : en
Pages : 449

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The activation of carbon dioxide by transition metal complexes has been extensively studied. both experimentally and theoretically. 1 Central reactions in this chemistry are the insertion of C02 into M-X bonds. where X = H. C. 0. and N. (eq. 1-4). We are presently investigating the mechanistic aspects of these reaction processes and will herein deSCribe our current level of understanding. Comparisons of the pathway of the carbon-carbon bond fonning process in transition metal chemistry with the well known analogous chemistry involving organolithium reagents will be presented. Furthermore. the role of these reaction types in both homogeneous and heterogenous catalytic processes leading to useful chemicals will be elaborated. _OM> (1) lMt-H + ~ lMlopi _OM> (2) [Mt-R + C0. 2 [M]0. 2CR _OM> (3) [Mt-OR+ ~ [M]0. 2COR _OM> (4) [Mt-NR2 + C0. 2 [M]~CNR2 Insertion of C02 into the Metal-Hydride Bond. The reaction of anionic group 6 (Cr. Mo. W) transition metal hydrides with carbon dioxide to afford metalloformates occurs readlly at ambient temperature and 2 reduced pressures of carbon dioxide. This insertion process is referred to the normal pathway (Scheme 1). There are no documented cases of C02 insertion into the metal hydride bond to provide the alternative. metallocarboxylic acid. isomer (referred in Scheme 1 as abnormal). 3 Recent theoretical studies ascribe this preference to an unfavorable electrostatic interaction and poorer orbital overlap in the latter pro 4 cess. Nevertheless.

Author: Dalton Bodine Burks
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 292

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The majority of energy produced in the world is derived from fossil fuels which are finite and have deleterious environmental effects. For a sustainable and environmentally-friendly energy future, alternative, renewable energy sources are desired. Two reactions that could have applications towards developing renewable energy sources are water oxidation to produce hydrogen and carbon dioxide reduction to form various products (e.g. formic acid or carbon monoxide); however, these reactions require catalysts to efficiently produce the desired products. Efforts to synthesize, characterize, and study catalysts for these reactions are discussed in this dissertation. The first chapter serves as an introduction to energy-related catalytic reactions. In Chapter 2, 6,6ʹ-dihydroxybipyridine (6,6ʹ-dhbp)-a protic ligand used with several metals to produce catalysts for energy-related reactions-is studied to determine its thermodynamic acidity. In the following chapter, 6,6ʹ-dhbp is used as a ligand with copper to form complexes that are water oxidation catalysts. Chapters 4 and 5 focus on iridium and ruthenium complexes containing new bidentate ligands composed of pyridinol and N-heterocyclic carbenes (NHCs). These complexes, along with an iridium complex of 6,6ʹ-dhbp, were used as catalysts for the hydrogenation of carbon dioxide to formate and the reverse dehydrogenation of formic acid to carbon dioxide and hydrogen. However, the complexes containing the new bidentate pyridinol-NHC ligands were found to be precatalysts as they undergo transformations and decomposition during the course of the reaction. A nickel-pincer complex with a protic CNC-pincer derived of pyridinol and NHCs was used as a photocatalyst for carbon dioxide reduction in Chapter 6. The protic state of the hydroxy group in the 4-position of the pyridine ring was determined to be important for catalysis, as the deprotonated hydroxy group results in 10 times the catalytic ability as the protonated form. In the penultimate chapter, ruthenium-pincer complexes that are active carbon dioxide photoreduction catalysts are studied mechanistically by UV/vis and IR spectroscopies. The most active catalyst was studied in greater detail with real-time IR spectroscopy to help elucidate potential reaction pathways. The final chapter serves as a conclusion to summarize the results discussed in the dissertation.

Author: Kun Zhao
Publisher:
ISBN:
Category :
Languages : en
Pages : 179

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Mots-clés de l'auteur: CO2 hydrogenation ; heterogeneous catalysis ; methanation ; reaction mechanism ; surface adsorption ; adsorbates ; catalyst ; metal oxide ; IR spectra ; data analysis.

Author: Wilbur Arthur Lazier
Publisher:
ISBN:
Category : Catalysis
Languages : en
Pages : 348

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Author:
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ISBN:
Category :
Languages : en
Pages :

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A mechanism is proposed for the formation of methanol and other oxygenated organic products from carbon monoxide and hydrogen over metal oxide catalysts. These products are formed via the associative adsorption of carbon monoxide on the oxygen of the metal oxide surface, followed by reduction with metal activated hydrogen. Carbon dioxide is dissociated to chemisorbed CO and O. This explains why over-reduction of methanol catalysts results in the formation of hydrocarbons rather than methanol. The mechanism of methanol formation with combined heterogeneous nickel boride and homogeneous molybdenum hexacarbonyl is postulated. (JSR).

Author: William M. Ayers
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 232

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Annotation Papers from a symposium sponsored by the Division of Colloid and Surface Chemistry at the 191st Meeting of the ACS, NYC, Apr. 1986. Discusses the need to develop catalytic reactions for converting CO2 to products such as methanol and methane. Topics range from general issues to theoretical treatments of carbon dioxide bonding followed by various catalytic approaches. Annotation(c) 2003 Book News, Inc., Portland, OR (booknews.com).

Author: Xiao-Feng Wu
Publisher: Springer
ISBN: 3319777572
Category : Science
Languages : en
Pages : 261

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​The series Topics in Current Chemistry Collections presents critical reviews from the journal Topics in Current Chemistry organized in topical volumes. The scope of coverage is all areas of chemical science including the interfaces with related disciplines such as biology, medicine and materials science. The goal of each thematic volume is to give the non-specialist reader, whether in academia or industry, a comprehensive insight into an area where new research is emerging which is of interest to a larger scientific audience. Each review within the volume critically surveys one aspect of that topic and places it within the context of the volume as a whole. The most significant developments of the last 5 to 10 years are presented using selected examples to illustrate the principles discussed. The coverage is not intended to be an exhaustive summary of the field or include large quantities of data, but should rather be conceptual, concentrating on the methodological thinking that will allow the non-specialist reader to understand the information presented. Contributions also offer an outlook on potential future developments in the field.

Author:
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Category :
Languages : en
Pages : 3

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Photo-promoted hydrogenation of CO2 at 1 atm total pressure over a number of catalysts was investigated. CO was the principal product of both the dark and photo-promoted reactions in the presence and absence of water vapor. The first batch of a Co-Mo-Al-Oxide preparation was the most active photocatalyst investigated, giving 0.35 molec. of CO per incident photon of white light and, in the presence of water vapor, a yield of CO equal to 10 times its concentration at thermal equilibrium. Studies of this system included the action spectrum for formation of CO and the dependence of rate on the CO2/H2 ratio, on temperature and on intensity of white light. The catalyst was a heterogeneous mixture of several phases. Subsequent batches of Co-Mo-Al-Oxide, prepared according to the original protocol, differed from the first batch in composition and were less active photocatalysts. Similar studies were carried out using pristine and platinized DeGussa P-25 Tio2 as catalyst.