Using waste to treat waste: Red mud induced hierarchical porous γ-AlOOH and γ-Al2O3 microspheres as superior Pd support for catalytic reduction of 4-nitrophenol

Toward the imperative treatment of the industrial wastewater containing 4-nitrophenol (4-NP) and industrial solid waste red mud (RM), an innovative approach of “Using waste to treat waste” is developed. Valuable element Al is leached from the RM first, the resultant NaAlO2 solution is hydrothermally converted to γ-AlOOH hierarchical porous microspheres (RM γ-AlOOH HPMSs, average diameter: 2.0 μm, SBET: 77.81 m2 g–1, pore volume: 0.38 cm3 g–1) in the presence of urea. The subsequent mild thermal conversion results in γ-Al2O3 hierarchical porous microspheres (RM γ-Al2O3 HPMSs). Both of the RM γ-AlOOH and RM γ-Al2O3 HPMSs are employed as the Pd catalyst support for the catalytic reduction of 4-NP. Particularly, the as-obtained composite Pd/RM γ-AlOOH and Pd/RM γ-Al2O3 exhibit excellent catalytic activities with superior knor as 8204.5 and 4831.4 s–1 g–1, respectively, significantly higher than that of most Pd based catalysts. Moreover, the excellent catalytic stability and durability of the Pd/RM γ-AlOOH and Pd/RM γ-Al2O3 within 10 successive cycles of reduction enable the present industrial solid waste RM induced γ-AlOOH and γ-Al2O3 HPMSs as great promising Pd catalyst support for the reduction of the industrial wastewater containing 4-NP.