Effect of Synthesis Conditions on the Catalytic Performances of CuO/Al2O3 in Microwave-enhanced Fenton-like System

Background: In previous work, we successfully prepared CuO/Al2O3 catalysts and evaluated their catalytic activity, kinetics and degradation mechanism for Fenton-like oxidation of p-nitrophenol (PNP) under microwave irradiation. However, we did not study the effect of important preparation parameters on the activities of catalysts. Objectives: (1) The effect of preparation conditions: CuSO4 concentration of the impregnating solution, Al2O3 to CuSO4 solution ratio, type and concentration of precipitant and calcination temperature on the physico-chemical properties and catalytic activity were studied. (2) The catalytic performance of the Fenton-like oxidation reaction of PNP under microwave irradiation was evaluated and correlated with the characterization results. (3) The stability and catalytic mechanism of the catalysts were investigated. Methods: The CuO/Al2O3 catalyst was prepared by the impregnation deposition method. The 20 g pretreated Al2O3 particles were immersed in 0.6 mol/L Cu (NO3)2 solution and 0.4 mol/L NaOH solution for 24 h before and after. After cleaning and drying, the samples were calcined in an air muffle furnace for 4 h at a certain temperature to obtain CuO/Al2O3 catalyst. Then the catalyst was characterized and catalyzed. Results: XRD, BET and FESEM results have demonstrated that the catalyst claimed at 300 and 350°C showed a smaller size, a higher specific surface area and a better distribution of the CuO species than their counterparts prepared at higher calcination temperatures. The CuO/Al2O3 catalyst claimed at 300 and 350°C also showed higher removal efficiencies for PNP than other catalysts prepared at higher calcination temperatures. Conclusion: It was found that the catalysts prepared at 350°C as calcination temperature showed higher surface area, smaller CuO particle size, and uniform CuO particle size distribution, and consequently showed better catalytic activities with better stability and reusability. Moreover, the XPS results of the catalysts showed a decrease in the Isat/Ip ratio after microwave enhanced Fenton- like reaction, confirming that CuO species has been reduced to Cu2O to some extent.