Catalytic conversion of plastic wastes using cost-effective bauxite residue as catalyst into H2-rich syngas and magnetic nanocomposites for chrome(VI) detoxification.

Red mud (RM) as bauxite residue from aluminum plant was investigated as cost-effective catalyst for pyrolysis and ex-situ catalytic conversion of plastic wastes into H2-rich syngas and magnetic carbon nanocomposites. The results showed that the introduction of RM catalyst elevated gas yield from 23.8 to 60.3 wt% as a rise of catalytic temperature (700-850 °C), due to its high iron activity for scission of polymer chains. Furthermore, the endothermic nature of cracking reactions of hydrocarbons led to the maximum H2 production of 28.8 mmol gfeed-1 and 63 vol% at 850 °C. The carbon/RM nanocomposites were comprehensively evaluated by multiple characterizations. High-resolution TEM indicated considerable carbon nanotubes(CNTs) depositing on the RM surface that modified iron sites dispersion and diminished nanoparticle size of iron at higher temperature of ≥800 °C. XRD and XPS results confirmed that higher temperature provided carbon components surrounding iron species to form metallic iron. The carbon/RMs were initially applied to chromium(VI) removal in sewage. RM-800 delivered high-profile adsorption capacity of 193.8 mg g-1, mainly attributed to the synergistic effect of chemical reduction by sufficient Fe0 exposure and CNTs growth promoting electrostatic attraction and electron transfer capacity. Furthermore, the correlation mechanism between catalytic temperature and the evolution of products and was discussed.