Universität zu Köln

Badea, Désirée ORCID: 0000-0002-8837-9988 (2025). New Metal Oxides from Syntheses under Extreme Conditions. PhD thesis, Universität zu Köln.

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Abstract

This PhD dissertation explores fundamental research on oxygen-containing compounds formed under extreme conditions, including highly alkaline environments, high pressures in the multi anvil press and high O2 pressures in autoclaves. As part of a collaboration with BASF, the study also focused on the synthesis and characterization of novel compounds relevant to ethylene oxide catalyst production. Ba[TcO3N] was synthesized by reacting ammonium pertechnetate with Ba(OH)2 · 8 H2O under highly alkaline conditions. Structural characterization revealed isolated [TcO3N]2− tetrahedra, providing insights into technetium behavior in alkaline environments, crucial for nuclear waste management. Raman spectroscopy, X-ray absorption near edge structure spectroscopy and density functional theory calculations confirmed the Tc +VII oxidation state and clarified its bonding. In similar approaches, mixed anionic nitridotrioxometallates, specifically K3[ReO4][ReO3N] and K3[TcO4][TcO3N], were synthesized by reacting ammonium pertechnetate and perrhenate in KOH hydrofluxes. Structural analysis using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and quantum chemical calculations confirm the presence of Re N and Tc N bonds, which are key to the unique structure of these compounds. Additional syntheses of single crystals of A3[ReO4][ReO3N] (A = Rb, Cs) and A'2[ReO3N] (A' = K, Cs) were carried out, with further characterization by Raman spectroscopy and quantum chemical calculations. The work also explores the synthesis of new iridium compounds, including Ba2[Ir(OH)6](OH)2, of which the crystal structure has been elucidated. Similar attempts led to the synthesis of Ba2.4Sr1.6[Ir(OH)6](OH)6, also analyzed by single crystal X-ray diffraction. By using a Walker-type multi anvil press, a new ternary silver-lead oxide, Ag2PbO3, was obtained from Ag2O and PbO2. The structure and composition were confirmed by single crystal X-ray diffraction, powder X-ray diffraction and X-ray photoelectron spectroscopy, showing silver and lead coordination in a rock-salt type structure. In addition to fundamental research on compounds from extreme conditions, the ethylene oxide catalysis was addressed in collaboration with BASF. Therefore, in the last part of this work powder X-ray diffraction and energy-dispersive X-ray spectroscopy data were obtained of fresh and spent catalyst samples provided during the collaboration with BASF. Furthermore, promoter solutions which are typically used for the production of the catalyst were combined resulting in the compounds [Ag(μ-en)][ReO4] and [Ag2(DHPP)](C2O4). Structural analyses were conducted for both compounds using single crystal X-ray diffraction. The thermal analysis of [Ag(μ-en)][ReO4] revealed that it decomposes to elemental Ag, in analogy with industrial processes. In ethylene oxide catalysis, Ag serves as the primary catalyst for selective oxidation, while Re and Cs enhance activity and selectivity, and Cl optimizes surface properties. Therefore, additional experiments aimed to identify new intermediates, focusing on Ag, Re, Cs and Cl under various extreme conditions.

Item Type:	Thesis (PhD thesis)
Translated title:	Title Language Neue Metalloxide aus Synthesen unter extremen Bedingungen German
Creators:	Creators Email ORCID ORCID Put Code Badea, Désirée nc-badeads@netcologne.de orcid.org/0000-0002-8837-9988 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-785886
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Inorganic Chemistry
Subjects:	Chemistry and allied sciences
Uncontrolled Keywords:	Keywords Language Hydroflux UNSPECIFIED Oxoanions UNSPECIFIED Technetium UNSPECIFIED Rhenium UNSPECIFIED Silver UNSPECIFIED High pressure UNSPECIFIED XPS UNSPECIFIED Raman UNSPECIFIED Quantum chemistry UNSPECIFIED X-ray UNSPECIFIED XANES UNSPECIFIED EO catalysis UNSPECIFIED TG-DSC UNSPECIFIED Crystal structure UNSPECIFIED
Date of oral exam:	16 June 2025
Referee:	Name Academic Title Bruns, Jörn PD Dr. Ruschewitz, Uwe Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/78588