Catalytic ozonation with γ-Al2O3 sphere supported highly dispersed iron species: Preparation, performance and catalytic mechanism

Maximizing the number of active sites is important to obtain an excellent catalytic activity for supported metal catalysts. Herein, citric acid-modified Al 2 O 3 spheres in millimeter scale were employed as the porous support for loading iron species by a impregnation-calcination method using Fe(NO 3 ) 3 ‧9H 2 O as the metal precursor. A good dispersion of the iron species inside the Al 2 O 3 spheres was achieved, and the characterizations revealed that Fe sites were incorporated into the framework of Al 2 O 3 in the form of -[Al-O-Fe III ]- structure. The obtained Fe III /CA-Al 2 O 3 catalyst was found to have a significantly increased amount of surface Lewis acid sites (LAS), showing a better performance than the counterpart catalyst Fe 2 O 3 /Al 2 O 3 for p -nitrophenol (PNP) degradation. It was found that the presence of both oxidizable organic pollutants (as electron donator) and ozone was the prerequisite for observing the transformation from surface-ferric ( Fe III ) to surface-ferrous ( Fe II ) iron on the surface of Fe III /CA-Al 2 O 3 catalyst. In comparison with Fe 2 O 3 /Al 2 O 3 catalyst, the Fe III /CA-Al 2 O 3 catalyst also demonstrated a higher level of Fe II during the catalytic reaction, suggesting that it had more iron active centers for the catalytic reaction. The cycle of the redox couple Fe III and Fe II played an important role for producing the reactive oxygen species. This study confirms that the modification of γ-Al 2 O 3 spheres with citric acid enabled a highly homogeneous dispersion of iron within the support matrix, providing a feasible route for the synthesis of high-performance and low-cost iron-bearing catalysts for industrial application.