Entwicklung von Oxidationskatalysatoren für die luftsauerstoffbasierte Bleiche und Untersuchung der zugrunde liegenden molekularen Mechanismen
- Development of oxidation catalysts for bleaching applications using aerobic oxygen and investigation of the underlying molecular mechanisms
Dzierbinski, Adam; Palkovits, Regina (Thesis advisor); Schwaneberg, Ulrich (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2020
In the first part of this work, the effects of various aqueous bleach systems containing soda, H2O2 and different polyoxometalates (POMs) as catalysts have been investigated in the bleach of diverse stains by varying reaction conditions like washing duration, temperature and H2O2 concentration. The H2O2 concentration could be lowered significantly without significantly diminishing bleach performance. An activation of aerobic oxygen by Mn-Me3tacn as well as Na5[IMo6O24] could be achieved in autoclaves pressurised with 80 bar of synthetic air while the latter exhibited a higher baseline level in performance. A possible pre-activation of the POM via a release of peroxometalate species could be classified as very likely in subsequent experiments. One of the possible mechanisms at work could be the oxygen transfer to the molecular structure of the stain, thereby increasing its water solubility and thus enabling its removal from the textile. Based on these results the second part of this work deals with a mechanistic study of the catalytic epoxidation of unsaturated model substrates with peroxometalates and H2O2 in aqueous solution. The tested peroxometalate W2O112- exhibits a significantly higher activity than the isostructural Mo2O112-. The activation enthalpies and entropies of the epoxidation of allyl alcohol, maleic acid and itaconic acid were calculated based on kinetic investigations using the Eyring equation. These values were compared to energetic spans calculated via density functional theory for the catalytic cycles of W2O112- and Mo2O112-, respectively. For allyl alcohol epoxidation, TOF-determining transition states and intermediates were determined according to a method presented by Kozuch et al. By taking proton tunnelling into account, multiple states have to be considered when determining the energy span, thereby preventing an unambiguous statement if oxygen transfer or catalyst regeneration is rate-determining.