Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 20 of 24 for “"isotope exchange"”.
-
Iridium complexes as highly active catalysts for hydrogen isotope exchange and hydrogen borrowing processes
… found to be excellent catalysts for hydrogen isotope exchange and olefin hydrogenation processes. The work described within this thesis centres upon the expansion of these catalysts' reactivity in hydrogen isotope exchange, as well as the synthesis and application of a series of novel iridium …
-
Investigation of the Oxygen Isotope Exchange Between Carbon Dioxide and O3 via O(1D)
… an increasing enrichment in the heavy oxygen isotopes with altitude which preferential enrichment for 17O according to d17O =1.7 d18O. This is contrary to tropospheric CO2 where d17O ~ 0.5d18O. These isotope enrichments are transferred from O3 into CO2, but details of the mechanism are not …
-
On the design and further applications of iridium (I) complexes in hydrogen isotope exchange processes
… Application of these species in hydrogen isotope exchange (HIE) processes revealed more efficient catalysis and a wider solvent scope when X = BArF. Additionally, these findings have allowed for the development of a novel method for ortho-HIE in unprotected tetrazoles under basic …
-
Hydrogen-water isotope exchange in a trickle bed column by process simulation and 3D computational fluid dynamics modelling
… nuclear sites remove many contaminating debris isotopes, with the exception of tritium. This is because tritiated waters have traditionally been particularly difficult and expensive to treat while they can spread easily if they escape into the environment. The topic of separation and …
-
Antimony isotopes as indicators of redox reactions in aqueous systems: fractionation during Sb(V) reduction by sulfide and isotope exchange kinetics between dissolved Sb(III) and Sb(V)
… more precise understanding of the drivers of Sb isotope variation, the magnitude of isotopic fractionation for individual reactions must be determined. In this study, we determine the magnitude of isotopic fractionation in environmentally relevant reactions. We use anion exchange resin and …
-
Mechanism and Application of a Heterogeneous Catalytic Hydrogen-deuterium Exchange Reaction for Polyolefins
The mechanism of a heterogeneous catalytic H/D exchange reaction with polyolefins is investigated in this thesis. The model polymers used in this study were hydrogenated polybutadienes (hPBDs), and a metallocene linear low density polyethylene (LLDPE). When mixed at 170 ºC with isooctane, …
-
Nuclear Magnetic Resonance Studies of Lithium Metal Anodes
… conditions. NMR measurements show that the isotope exchange between a 6Li-enriched lithium metal and a natural abundance electrolyte depends significantly on the electrolyte and the corresponding SEI. A numerical model is developed to describe the processes during isotope exchange and is …
-
Nitrogen cycling in oxygen deficient zones : insights from δ15N and δ18O of nitrite and nitrate
The stable isotopes, δ15N and δ18O, of nitrite and nitrate can be powerful tools used to interpret nitrogen cycling in the ocean. In order to interpret isotope profiles, the isotope systematics of each process involved must be known. This thesis describes numerous experiments using both cultures of …
-
Understanding the ATP hydrolysis mechanism in myosin using computer simulation techniques
… drawn and related to experimental findings from isotope exchange and mutation studies. All three paths investigated follow a single-step associative-like mechanism (see movies at http://www.iwr.uni-heidelberg.de/groups/biocomp/fischer) and show very similar heavy-atom positions in the transition …
-
Symmetry Specific Study of Ozone Isotopomer Formation
The unusual isotope effect in the formation of the ozone molecule is not yet understood, even 25 years after its discovery. Furthermore, the experimental database is still unsatisfactory, particularly with regard to application of the heavy oxygen from ozone as an atmospheric tracer. To close a gap …
-
Interaction of aqueous U(VI) with goethite, montmorillonite, and UO2(s)
… and clay minerals. Aqueous U(VI) can also exchange uranium atoms with solids comprised of uranium which can potentially lead to changes in the morphology of the uranium-containing solids and affect their stability. First, the performance of multiple surface complexation models (SCMs) on …
-
Partial Oxidation of Hydrocarbons Over Ceria Zirconia Catalysts
… The most promising analytical technique is isotope exchange coupled with infrared spectroscopy and an inline mass spectrometer. Next, methane partial oxidation over ceria zirconia catalysts is studied with infrared spectroscopy. Methane and oxygen concentrations are modulated to …
-
Studies of unusual catalysis : a tale of four enzymes from diverse biosynthesis pathways
… (FAD) in an unusual manner. Positional isotope exchange and kinetic linear free energy relationship studies provide a direct experimental evaluation of the nucleophilic participation by reduced FAD during UGM catalysis. MoeZ from Amycolatopsis orientalis is a unique sulfur carrier …
-
Some reactions of methylsilane catalysed by metals
… at 273 K, and the catalysed hydrogen isotope exchange in methylsilane in the range 195 - 300 K have been studied using evaporated metal films of molybdenum, tungsten, rhodium, nickel, and gold.Chemisorption is strong, and is accompanied by dissociation of hydrogen bonded to silicon, …
-
Biogeochemical and phylogenetic signals of Proterozoic and Phanerozoic microbial metabolisms
… precursors including acetate and methanol, isotope exchange, or environmental processes such as methane oxidation. The phylogenetic relationship between substrate-specific methyl-corrinoid proteins provides insight into the evolutionary history of methylotrophic methanogenesis. The …
-
Unraveling the fingerprints of NOx using stable isotopes: Implications for NOx source partitioning and oxidation chemistry
<p>The nitrogen (N) and oxygen (O) stable isotope composition (δ15N & δ18O) of nitrogen oxides (NOx )may be a useful tool for constraining NOx emission sources as well as for understanding the atmospheric oxidation pathways responsible for its removal if various NOx sources and sink processes …
-
Advances in the isotopic analysis of biogenic phosphates and their utility in ecophysiological studies of aquatic vertebrates
… these types of data with analyses of the oxygen isotope compositions of the phosphate (δ¹⁸O(p)) and the carbon isotope compositions of the carbonate (δ¹³C(sc)) of teeth and bones, to determine whether the ingested water and diet, respectively, were fresh or marine. The power of this approach is …
-
Biogeochemical and phylogenetic signals of Proterozoic and Phanerozoic microbial metabolisms
… precursors including acetate and methanol, isotope exchange, or environmental processes such as methane oxidation. The phylogenetic relationship between substrate-specific methyl-corrinoid proteins provides insight into the evolutionary history of methylotrophic methanogenesis. The …
-
Chromium and uranium isotopic exchange kinetics and isotope fractionation during oxidation of tetravalent uranium by dissolved oxygen
Chromium (Cr) and Uranium (U) isotopes (53Cr/52Cr and 238U/235U ratios) are very powerful new geochemical tools in environmental remediation and paleoredox reconstruction studies. Correctly interpreting Cr and U isotopic compositions in groundwater and sed- imentary rock samples requires thorough …
-
Nitrogen cycling in oxygen deficient zones : insights from [delta]¹⁵N and [delta]¹⁸O of nitrite and nitrate
The stable isotopes, [delta]¹⁵N and [delta]¹⁸O, of nitrite and nitrate can be powerful tools used to interpret nitrogen cycling in the ocean. They are particularly useful in regions of the ocean where there are multiple sources and sinks of nitrogenous nutrients, which concentration profiles alone …
Page 1 of 2