Ultrasonic impregnation of MnO2/CeO2 and its application in catalytic sono-degradation of methyl orange

Abstract

MnO₂/CeO₂ catalyst was prepared by ultrasonic impregnation method. The traditional and stirring impregnation methods were used as control. Results showed that ultrasonic impregnation was the best synthesis method. The impregnation time was shortened from 120 min (traditional method) to 20 min, the specific surface area of catalyst was three times larger, and the catalytic activity of catalyst was also the highest. Furthermore, MnO₂ had crystalline structure and distributed uniformly on the support, CeO₂. The preparing conditions were further examined and the optimal conditions were found to be: 20 min of ultrasonic impregnation, 4.3 mol/L of manganese nitrate concentration and 450 °C of calcination temperature. The so prepared catalyst removed 94% of methyl orange in 30 min with a dosage of 0.5 g/L. The efficiency was 77.7% and 85.9% for traditional and stirring impregnation method under the same experimental conditions. The reaction process involved two stages: adsorption-dominated and degradation-dominated stages. The reaction rate constant of adsorption-dominated stage had little difference. However, compared with traditional impregnation, the reaction rate constant of degradation-dominated stage improved from 0.01 to 0.14 min^-1 by ultrasonic impregnation. Mechanism analysis showed that the activity of ultrasonic impregnation MnO₂/CeO₂ was improved by the effects of acoustic cavitation and ultrasound oscillation on solid-liquid transport and distribution status.

Keywords: Catalytic ultrasonic process; Methyl orange; MnO(2)/CeO(2); Ultrasonic impregnation.