Overall rate of aqueous-phase catalytic oxidation of phenol: pH and catalyst loading in¯uences Aurora Santos, Eva Barroso, Fe Âlix Garcõ Âa-Ochoa * Dpto. Ingenierõ Âa Quõ Âmica, Facultad de Cecncia Quimica, Universidad Complutense, 28040-Madrid, Spain Abstract The catalytic oxidation of phenol in aqueous-phase has been investigated using a commercial catalyst CuO±2(CuO)Cr 2 O 3 ± CrO 4 Ba±Al 2 O 3 at 400 K and an oxygen pressure of 8 atm, changing the pH and catalyst concentration. The phenol conversion, TOC consumption, the intermediates and the pH variation with time have been determined. An irreversible bonding of phenol on the catalyst surface has been found as a previous step to the phenol oxidation reaction. An overall pseudo-®rst order kinetic constant has been calculated for phenol conversion and values obtained at basic pH are lower than those calculated for acid pH media. An important homogeneous contribution for the phenol oxidation rate was found. However, the intermediates mineralization is notably in¯uenced by the catalyst load. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Copper catalyst; Phenol oxidation; Mineralization; Catalyst/liquid ratio 1. Introduction The problem of pollution reduction of the aqueous stream containing phenolic compounds is of great importance in waste waters from many industries (agroalimentary processes, pharmaceutical, ®ne che- mical, petrochemical, etc.). These ef¯uents cannot be treated through conventional processes of biological oxidation, because of their poor biodegradability. The process currently used is the wet oxidation or super- critical oxidation, which requires high pressures and temperatures, and consequently carries a high cost [1,2]. One of the most promising technologies for elim- inating phenolic compounds in waste waters is the heterogeneous catalytic oxidation of these aqueous streams under supercritical or intermediate conditions [3±5]. After this treatment, the refractory organic compounds as phenol are mineralized to CO 2 and H 2 O or converted to harmless intermediates which can be dealt with by a conventional process of biolo- gical degradation. Among the catalysts tested for phenol oxidation the copper oxides supported on alumina have been employed most frequently [6± 12] often using the slurry reactors to carry out the reaction. Therefore, a low catalyst concentration is usually employed. However, there is no agreement among the results reported by the previous works on the in¯uences of variables such as pH, catalyst concentration and catalyst leaches. Studies carried out on this topic show that the reaction involves a free radical mechanism, with an induction period before the steady-state regime is achieved, considering both Catalysis Today 48 (1999) 109±117 *Corresponding author. Tel.: +34-1-3944176; fax: +34-1- 3944171/14; e-mail: chapu@eucmax.sim.ucm.es 0920-5861/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0920-5861(98)00364-2