Carbon-supported iridium catalysts in the catalytic wet air oxidation of carboxylic acids: kinetics and mechanistic interpretation

Carbon-supported iridium catalysts were prepared by different incipient wetness impregnation methods and by organometallic chemical vapor deposition. The catalysts were characterized by N-2 adsorption, TPD, SEM and H-2 chemisorption measurements. The results obtained indicate a clear dependency of the metal-phase dispersion on the pre-treatment of the carbon support and the impregnation method. Their activity for catalytic wet air oxidation of butyric and iso-butyric acid aqueous solutions was investigated in a stirred reactor at 473 K and 0.69 MPa of oxygen partial pressure. The conversions obtained after 2 h were 43 and 52%, with respect to each carboxylic acid, when the most active catalysts were used. The measured conversions and initial reaction rates correlate well with the exposed metal area. A rate equation was determined from measurements of the initial reaction rates at different oxygen partial pressures, temperatures and catalyst mass loads. The results were modeled considering a heterogeneously catalyzed free-radical mechanism. (C) 2002 Elsevier Science B.V. All rights reserved.