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A novel composite catalyst prepared by fixing cobalt aluminate (CoAl 2 O 4) spinel on formed alumina carrier by impregnation-calcination route is reported, which can be used to efficiently activate peroxymonosulfate (PMS) to degrade p-nitrophenol (PNP). The internal laws of phase composition and preparation conditions are explored in detail, and the results show that the introduction of additional aluminum ions in the preparation process changes the coordination environment and the electronic state of cobalt ions, which leads to the transformation of spinel/inverted spinel in the composition, and further affects the activity and stability of the catalyst. The selected CoAl-Aaps-600 catalyst has high CoAl 2 O 4 content, showing good cycle performance and low cobalt leaching, and has great catalytic degradation performance at different temperatures and a wide pH range. Most notably, a fixed bed reactor packed with 20 g of CoAl-Aaps-600 exhibits excellent capacity to continuously treat 60 L of PNP solution with acceptable PNP removal ratio and low cobalt leaching content. Sulfate radical and singlet oxygen are identified as the main reactive oxygen species produced in CoAl-Aaps-600/PMS system, and the reaction mechanism is reasonably inferred. This work provides a potential application material and process for the treatment of continuous organic wastewater. [Display omitted] • CoAl 2 O 4 spinel is anchored on activated alumina pellets to activate PMS. • Occupying the octahedrons by aluminum ions is the crux to control the phase composition. • The catalyst has low cobalt leaching and high stability. • The continuous-flow reaction shows the long-term effectiveness of the catalyst. [ABSTRACT FROM AUTHOR]

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 (Co 2 AlO 4 /Al 2 O 3 -xSiO 2) were prepared by impregnation and high-temperature calcination using Al 2 O 3 -xSiO 2 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 Co 2 AlO 4 /Al 2 O 3 -xSiO 2 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 (Co 2 AlO 4 /Al 2 O 3 -0.25SiO 2) 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, Co 2 AlO 4 /Al 2 O 3 -0.25SiO 2 dosage, reaction temperature, initial pH value, and inorganic ions) on PNP removal were comprehensively investigated. Sulfate radical (SO 4 •−) and singlet oxygen (1O 2) are making a major contribution to the degradation of PNP. Moreover, a millimeter-scale catalyst (CoSiAl-0.25/Al 2 O 3 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. [Display omitted] • Co 2 AlO 4 /Al 2 O 3 -xSiO 2 were prepared by impregnation and calcination. • The ratio of Si–Al plays a key role in catalytic performance and reusability. • Sulfate radical (SO 4 •−) and singlet oxygen (1O 2) is the crucial reactive species. • The Co3+/Co2+ were the intrinsic active centers for PMS activation. • CoSiAl-0.25/Al 2 O 3 pellet exhibited better long-term PNP removal ability. [ABSTRACT FROM AUTHOR]