Search results for "uraani"
showing 9 items of 9 documents
Study of Ni, Pt, and Ru Catalysts on Wood-based Activated Carbon Supports and their Activity in Furfural Conversion to 2-Methylfuran
2018
Bio‐based chemicals can be produced from furfural through hydrotreatment. In this study, 2‐methylfuran (MF), a potential biofuel component, was produced with Pt, Ru, and Ni catalysts supported on wood‐based activated carbons. The catalytic hydrotreatment experiments were conducted in a batch reactor at 210–240 °C with 2‐propanol as solvent and 40 bar H2 pressure. Two types of activated carbon supports were prepared by carbonization and activation of lignocellulosic biomass (forest‐residue‐based birch and spruce from Finland). Both types of activated carbons were suitable as catalyst supports, giving up to 100 % furfural conversions. The most important factors affecting the MF yield were the…
Uranocenium: Synthesis, Structure, and Chemical Bonding
2019
Abstraction of iodide from [(η5 -C5 i Pr5 )2 UI] (1) produced the cationic uranium(III) metallocene [(η5 -C5 i Pr5 )2 U]+ (2) as a salt of [B(C6 F5 )4 ]- . The structure of 2 consists of unsymmetrically bonded cyclopentadienyl ligands and a bending angle of 167.82° at uranium. Analysis of the bonding in 2 showed that the uranium 5f orbitals are strongly split and mixed with the ligand orbitals, thus leading to non-negligible covalent contributions to the bonding. Investigation of the dynamic magnetic properties of 2 revealed that the 5f covalency leads to partially quenched anisotropy and fast magnetic relaxation in zero applied magnetic field. Application of a magnetic field leads to domin…
Isolation of a perfectly linear uranium(II) metallocene
2020
Reduction of the uranium(III) metallocene [(eta(5)-(C5Pr5)-Pr-i)(2)UI] (1) with potassium graphite produces the "second-generation" uranocene [(eta(5)-(C5Pr5)-Pr-i)(2)U] (2), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground-state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f(3) 6d(1). Appreciable covalent contributions to the metal-ligand bonds were determined from a computational study of 2, including participation from the uranium 5f and 6d orbitals. Whereas three unpaired electrons in 2 occupy orbi…
Multidimensional Skyrme-density-functional Study of the Spontaneous Fission of 238U
2015
We determined the spontaneous fission lifetime of 238U by a minimization of the action integral in a three-dimensional space of collective variables. Apart from the mass-distribution multipole moments Q20 (elongation) and Q30 (left–right asymmetry), we also considered the pairing- fluctuation parameter λ2 as a collective coordinate. The collective potential was obtained self-consistently using the Skyrme energy density functional SkM∗ . The inertia tensor was obtained within the nonperturbative cranking approximation to the adiabatic time-dependent Hartree–Fock– Bogoliubov approach. The pairing-fluctuation parameter λ2 allowed us to control the pairing gap along the fission path, which sign…
Syntheses, characterization and properties of Cu(II)-, Mo(VI)- and U(VI) complexes with diaminotetraphenolate ligands
2013
Uranium( iv ) cyclobutadienyl sandwich compounds: synthesis, structure and chemical bonding
2019
The 1 : 1 reactions of uranium(IV) tetrakis(borohydride) with the sodium and potassium salts of the cyclobutadienyl anion [C4(SiMe3)4]2− (Cb′′′′) produce the half-sandwich complexes [Na(12-crown-4)2][U(η4-Cb′′′′)(BH4)3] and [U(η4-Cb′′′′)(μ-BH4)3{K(THF)2}]2. In the 1 : 2 reaction of U(BH4)4 with Na2Cb′′′′, formation of [U(η4-Cb′′′′)(η3-C4H(SiMe3)3-κ-(CH2SiMe2)(BH4))]− reveals that a Cb′′′′ ligand undergoes an intramolecular deprotonation, resulting in an allyl/tuck-in bonding mode. A computational study reveals that the uranium–Cb′′′′ bonding has an appreciable covalent component with contributions from the uranium 5f and 6d orbitals. peerReviewed
Säteilyn aiheuttamat värinmuutokset korkeasaantoisessa massassa
2017
Korkeasaantoisen havusulfaattimassan sähkömagneettisen säteilyn aiheuttama kellastuminen aiheutuu puun natiiveista sekä sulfaattikeiton aikana syntyvistä kromoforeista. Kromoforit ovat kemiallisia rakenteita, jotka absorboivat säteilyä näkyvän valon alueelta, minkä seurauksena syntyy värejä. Kellastumisen aiheutumiseksi kemialliseen rakenteeseen on synnyttävä kromoforisia rakenteita, jotka absorboivat näkyvää valoa sini-viher-alueella. Havupuiden osalta kromoforisia rakenteita esiintyy ligniinissä, uuteaineissa sekä hiilihydraattien johdannaisissa. Lopputyöni kirjallisessa osassa perehdytään havupuiden natiivien sekä sulfaattikeiton aikana syntyvien kromoforien ominaisuuksiin sekä muodostum…
Synthesis of trans-disubstituted-2,3-dihydrobenzofurans by a formal [4 + 1] annulation between para-quinone methides and sulfonium salts
2018
An efficient protocol for the synthesis of trans-disubstituted-2,3-dihydrobenzofurans through [4 + 1] annulation of para-quinone methides with sulfonium salts has been developed. Under very mild conditions this unprecedented reaction occurs in good to excellent yields (up to 99%), offering a straightforward access to a variety of 2,3-dihydrobenzofurans.