Enhancing the stability of Mn-Ce-OWETOX catalysts using potassium

Mn-Ce-O composite catalysts are being widely advocated in sub- and supercri tical catalytic wet oxidation (WETOX) for the mineralization (i.e. complete conversion to CO2) of toxic organics contained in aqueous streams. Catalyt ic WETOX of CHO-containing compounds over Mn-Ce-O catalysts is accompanied with undesirable heavy polymers building upon the catalyst surface, thereby leading to severe loss in catalytic activity and mineralization selectivit y. Hence, new potassium-doped Mn-Ce-O mixed oxide catalysts (Mn/Ce atomic r atio = 1) synthesized by co-precipitation/impregnation were tested for the destruction of phenolic model wastewaters in a batch slurry reactor using o xygen and very mild reaction conditions. Remarkable improvements in mineral ization selectivity were attained upon addition of potassium. Complete remo val of the organic pollution, with mineralization selectivity exceeding 95% , was achieved within 10-20 min over fresh K-Mn-Ce-O catalyst. Virtually, t otal elimination of organic carbon was also achieved using the same catalys t 3 times without any regeneration. Likewise, the stability to leaching of the WETOX catalytic ingredients was very high as confirmed by analysis of t he treated solutions. Characterization of fresh and used Mn-Ce-O and K-Mn-C e-O catalysts was conducted using nitrogen adsorption, temperature-programm ed reduction (TPR) and temperature-programmed oxidation (TPO), infrared spe ctroscopy (FTIR), CHN elemental analysis and X-ray diffraction (XRD) techni ques. These techniques corroborated the drastic reduction in carbonaceous d eposits on the catalyst surface and the significant enhancement in stabilit y of the K-doped catalysts. These improvements were discussed in terms of m odification of the redox properties of cerium and manganese through interac tions with potassium in the doped Mn-Ce-O catalysts. (C) 2001 Elsevier Scie nce B.V. All rights reserved.