Catalytic de-chlorination of products from PVC degradation by magnetite (Fe3O4)

This contribution provides a systematic theoretical thermo-kinetic study of the initial reactions between Fe3O4(111) surface, as a representative model for metal oxides in electric arc furnace dust (EAFD) with HCl and selected chlorinated hydrocarbons, as major products from thermal degradation of PVC. Formation of the experimentally observed iron chloride occurs by subsequent dissociative addition of HCl molecules followed by H migration into a surface hydroxyl group. We provided Arrhenius parameters for reactions dictating the conversion of iron oxide into its chloride. In the course of the interaction of chlorinated alkanes and alkenes with the Fe3O4 surface, the opening channel in the dissociative addition route requires lower activation barriers in reference to the direct HCl elimination pathways. However, sizable activation barriers are encountered in the subsequent beta C-H bond elimination step. Estimated electronic charges confirm the nature of surface Fe-Cl bonds as Lewis acid - base pair. The obtained accessible reaction barriers for reactions of chlorinated alkanes and alkenes with the title iron oxide demonstrate that the latter serve as active catalysts in producing clean olefins streams from chlorinated alkanes. Results from this study should be instrumental to understand, on a precise atomic scale, mechanisms operating in fixation of halogens on transitional metal oxides; a viable thermal recycling approach for polymeric materials laden with halogenated constituents.