Ce 3d XPS study of composite CexMn1 xO2 y wet oxidation catalysts

Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: a review.

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 with 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 catalytic 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 reducing both phenol concentration and total organic carbon (TOC). All catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR) and nitrogen adsorption techniques. Systematic shifts in binding energy, diffraction angle, and reduction temperature were observed in the XPS, XRD and TPR spectra, respectively. XPS and XRD data revealed the occurrence of significant interactions between Mn and Ce oxides, resulting in the evolution of textural, structural and oxidation state with composition. TPR analysis showed that the interaction between Mn and Ce greatly improved the oxygen storage capacity of manganese and cerium oxides as well as oxygen mobility on the surface of catalyst. Catalytic active sites have been ascribed to manganese oxide species exhibiting higher oxidation state. Furthermore, XPS revealed that the most active catalyst, i.e. Mn/Ce 6/4, exhibits an electron-rich surface which may be very important in the activation of adsorbed oxygen.

Composition–activity effects of Mn–Ce–O composites on phenol catalytic wet oxidation

An assessment of supercritical water oxidation (SCWO). Existing problems, possible solutions and new reactor concepts

Mixed (Al–Fe) pillared clays are very efficient solid catalysts for oxidation of organic compounds in water by hydrogen peroxide. We have shown that in rather mild experimental conditions (atmospheric pressure, T≤70°C) and with a low excess (20%) of hydrogen peroxide, phenol was rapidly converted, mainly to CO2, without significant catalyst leaching. The (Al–Fe) pillared clay catalyst (called FAZA) can be used several times without any change of its catalytic properties. According to the low leaching observed and a previous Mossbauer spectroscopy study, the iron species appear to be strongly bonded to the aluminium pillars.

Catalytic wet peroxide oxidation over mixed (Al-Fe) pillared clays

The basic, subcritical wet oxidation process and the two main modifications (supercritical and catalytic oxidation) are briefly presented. Some design considerations of the processes and the oxidation kinetics which directly affects the reactor volume and process economics are also discusssed.

J Levec

Papers

Wet oxidation processes for treating industrial wastewaters