Synergistic effect between Mn and Ce for active and stable catalytic wet air oxidation of phenol over MnCeOx

Abstract

A series of MnCeOx catalysts for the catalytic wet air oxidation (CWAO) of phenol is developed by a redox-precipitation preparation method. Among them, Mn9Ce1Ox (Mn/Ce = 9:1) shows excellent activity and stability which can achieve TOC conversion of 88.1 % in 60 min at 70 °C and retain stable for five consecutive runs. Even at 50 °C, Mn9Ce1Ox can reach a phenol conversion of 84. 2% and a TOC conversion of 73.8 %. The roles of Mn valence state and Ce modification in the catalytic performance of Mn9Ce1Ox are extensively investigated by XRD, BET, Raman, H2-TPR and XPS. It is found that high Mn4+ concentration favors phenol adsorption and oxidation while high Mn3+ concentration favors oxygen activation. Ce optimizes the Mn4+/Mn3+ ratio and thus enhances catalytic activity. Additionally, Ce retains the structure of the catalyst and prevents Mn4+ and Mn3+ from being reduced to Mn2+, which contributes the good stability.