Catalytic activity, water resistance and stability of hematite nanomaterials in oxidative removal of polychlorinated aromatic hydrocarbons can be simultaneously enhanced through facet engineering

Abstract

Iron oxides are commonly used catalysts for the removal of polychlorinated aromatic hydrocarbons from incinerators. Here, we provide a proof of concept that facet engineering can be exploited to simultaneously improve the catalytic activity, water resistance and stability of iron oxides. Using 1,2-dichlorobenzene oxidation as a surrogate reaction, we show that α-Fe₂O₃ nanorods with predominantly exposed {110} facets (NR-{110}) exhibit lower T_50% and T_90% (temperatures of 50% and 90% removal) and higher CO₂ selectivity under a dry condition than α-Fe₂O₃ nanoparticles with {012} facets, α-Fe₂O₃ nanosheets with {001} facets, and commercial α-Fe₂O₃. NR-{110} also exhibits superior water resistance (without exhibiting the “V-shaped” curve in 1,2-dichlorobenzene removal originated from the competitive adsorption of water) and much better stability. Spectroscopic evidence based on pyridine-adsorbed Fourier transform infrared and X-ray photoelectron spectroscopy, chemisorption analysis based on O₂ temperature-programmed desorption, H₂ temperature-programmed reduction and H₂O temperature-programmed desorption and theoretical calculations demonstrate that the higher abundance of Lewis and Brønsted acid sites, higher concentration of surface active oxygen, more negative adsorption energy and lower C–Cl bond broken energy barrier associated with the (110) facet collectively enable fast reaction kinetics and more complete contaminant destruction. Additionally, the facet-specific interaction mode of water gives greater water resistance, and the abundant Brønsted acid sites on the (110) facet effectively provide H⁺ to prevent the accumulation of chloride ions, thus enhancing stability.