Composition-activity effects of Mn-Ce-O composites on phenol catalytic wetoxidation

Mn-Ce-O composite catalysts have been widely used in sub- and supercritical catalytic wet oxidation of toxic organics contained in aqueous streams. In order to investigate their composition-activity relationship, 11 samples w ith Ce/(Mn + Ce) atomic bulk ratios ranging from 0 to 100% were prepared by co-precipitation. Phenol was selected as a model pollutant and the catalyt ic oxidation was carried out in a batch slurry reactor using oxygen as the oxidizing agent under mild reaction conditions. The results showed that the catalytic activity was greatly influenced by the catalyst composition. The catalyst with Mn/Ce ratio = 6/4 was found to be the most active in reducin g both phenol concentration and total organic carbon (TOC). All catalysts w ere characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffract ion (XRD), temperature programmed reduction (TPR) and nitrogen adsorption t echniques. Systematic shifts in binding energy, diffraction angle, and redu ction temperature were observed in the XPS, XRD and TPR spectra, respective ly. XPS and XRD data revealed the occurrence of significant interactions be tween Mn and Ce oxides, resulting in the evolution of textural, structural and oxidation state with composition. TPR analysis showed that the interact ion between Mn and Ce greatly improved the oxygen storage capacity of manga nese and cerium oxides as well as oxygen mobility on the surface of catalys t. Catalytic active sites have been ascribed to manganese oxide species exh ibiting higher oxidation state. Furthermore. XPS revealed that the most act ive catalyst, i.e. Mn/Ce 6/4, exhibits an electron-rich surface which may b e very important in the activation of adsorbed oxygen. (C) 2001 Elsevier Sc ience B.V. All rights reserved.