Catalytic de-halogenation of halogen-containing solid wastes by nanostructures of transition metals and their oxide configurations

Oday H. Ahmed

This thesis presents a series of scientific investigations examining the potential dual role for nanostructure of several 3d transition metals and their oxides in the catalytic de-halogenation of halogen laden materials as well as their mediating formation of toxic halogenated aromatics through accurate density functional theory (DFT) calculations. These investigations have been instrumental to (i) understand, on a precise atomic scale, mechanisms operating in fixation of halogens on transitional metal and their oxides, (ii) design of a large-scale catalytic upgrading unit that operates to extract the valuable metals loads from electric arc furnace dust (EAFD) and (iii) provide important fingerprints for environmental burdens associated with thermal recycling of e-waste and subsequent generation of notorious dioxins compounds and phenoxy-type environmental persistent free radicals (EPFRs). Herein, we have carefully benchmarked the accuracy of systematically obtained results versus experimental values pertinent to investigated systems, namely, lattice parameters, density of states and surface relaxations. The initial part of the dissertation focuses on the reaction mechanisms of major products from thermal decomposition of polyvinyl chloride (PVC) and brominated flame retardants (BFRs) with nanostructures (clusters and surfaces) of hematite (α-Fe2O3), zincite (ZnO) and magnetite (Fe3O4). The detailed kinetic analysis indicates that dissociative adsorption of hydrogen halides molecules, the major halogen fragments from thermal degradation of halogen laden materials, over those metal oxide structures affords oxyhalides structures via modest activation barriers. Transformation of oxyhalides into metal halides occurs through two subsequent steps, further dissociative adsorption of hydrogen halides over the same structures followed by the release of H2O molecule. In the course of the interaction of halogenated alkanes and alkenes with the selected metal oxide structures, the opening channel in the dissociative addition route requires lower activation barriers in reference to the direct HCl/Br elimination pathways. However, sizable activation barriers are encountered in the subsequent β C-H bond elimination step. The obtained accessible reaction barriers for reactions of halogenated alkanes and alkenes with the title metal oxides demonstrate that the latter serve as active catalysts in producing clean olefins streams from halogenated alkanes. Finally, we examined the dissociative adsorption of a phenolic molecules on Cu and Fe surfaces and their partially oxidized configurations to elucidate the specific underpinning mechanism of the title reaction and the kinetics feasibility to germane to generate phenolate-type EFPRs. Our simulated results show that dissociative adsorption of the phenol molecule is kinetically and thermodynamically preferred over the partially oxidized configuration in reference to neat surfaces. Computed charge transfer and density of state (DOS) indicates accumulation of spin density on the phenolic’s O following fission of the O-H bond. Obtained results shall be instrumental in efforts that aim to recycle the non-metallic fraction in e-waste.

Catalytic de-halogenation of halogen-containing solid wastes by nanostructures of transition metals and their oxide configurations

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