Abstract
A series of ZnFe 2− x Al x O 4 spinel type catalysts prepared by sol–gel method have been characterized and tested for catalytic wet oxidation (CWO) of phenol with pure oxygen. The iron species existed in these materials as aggregated iron oxide clusters and Fe 3+ species in octahedral sites. With a decrease in iron content the concentration of the first iron species decreased and the latter increased. Complete phenol conversions and high chemical oxygen demand (COD) removals were obtained for all catalysts during phenol degradation at mild reaction conditions (160 °C and 1.0 MPa of oxygen pressure). Increasing with the concentration of Fe 3+ species in octahedral sites, induction period became significantly shortened. After phenol was completely degraded, the concomitant recycling of the leaching Fe 3+ ions back to the catalyst surface was observed, and in this case it is possible to perform successful CWO reactions with some cycles. It is also suggested that during the reaction the Fe 3+ cations coordinated in octahedral sites in the ZnFe 2− x Al x O 4 catalysts are resistant to acid leaching, but the reduced Fe 2+ cations become much more labile, leading to increased Fe leaching.
Published Version
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