Cobalt-aluminum spinel supported on modified γ-alumina for peroxymonosulfate activation: Si-Al ratio of support to optimize performance and reusability

Abstract

The development of cobalt-based supported catalysts with high PMS catalytic activity and stability by adjusting the composition of the support is highly desirable yet remains scarce. In the work, a series of catalysts (Co₂AlO₄/Al₂O₃-xSiO₂) were prepared by impregnation and high-temperature calcination using Al₂O₃-xSiO₂ with a low Si-Al ratio as the support. Measurement techniques such as XRD, XPS, UV-DRS, FTIR, BET, SEM and HRTEM were used to characterize textural and chemical properties (ratio of Co³⁺/Co²⁺, specific surface area, pore size, pore volume, etc.). The ratio of Co³⁺/Co²⁺ and pore volume of Co₂AlO₄/Al₂O₃-xSiO₂ can be turned by controlling the ratio of Si to Al, which are closely related to the catalytic performance and reusability of the catalysts. The optimized catalyst (Co₂AlO₄/Al₂O₃-0.25SiO₂) can completely degrade 10 mg/L p-nitrophenol (PNP) in 40 min in the pH range of 3-9 with excellent reusability. The effects of several reaction parameters (i.e., PMS dosage, Co₂AlO₄/Al₂O₃-0.25SiO₂ dosage, reaction temperature, initial pH value, and inorganic ions) on PNP removal were comprehensively investigated. Sulfate radical (SO₄•^-) and singlet oxygen (¹O₂) are making a major contribution to the degradation of PNP. Moreover, a millimeter-scale catalyst (CoSiAl-0.25/Al₂O₃ pellet) was prepared by sol adsorption and high-temperature calcination method, which maintained high oxidation activity after treatment of 18 L wastewater (PNP of 10 mg/L) in a continuous flow process. The method is simple and easy to operate on a large scale, providing a new perspective on the design and preparation of cobalt-aluminum spinel catalysts for activated PMS.

Keywords: Cobalt-aluminum spinel; Heterogeneous catalysis; SR-AOPs; Wastewater treatment; γ-Al(2)O(3).