Dispersion and Activity of Molybdena-Alumina Catalysts Prepared by Impregnation and Solid/Solid Wetting Methods

Abstract

Alumina-supported molybdena catalysts were prepared by both the standard incipient wetness method and by mixing MoO3 and Al2O3 (solid/solid wetting), followed by thermal treatment at 500°C under dry or wet 02 atmospheric conditions. These catalysts were characterized by means of O2 chemisorption at -78°C, CO2 uptake at ambient temperature, X-ray diffraction (XRD), and electron spin resonance (ESR) techniques. Activities of the catalysts were determined for partial oxidation of methanol and hydrodesulfurization of thiophene at atmospheric pressure. XRD results suggest high dispersion of Mo-oxide on alumina support irrespective of their method of preparation. However, O2 and CO2 uptake measurements reveal partial coverage of the A1203 support surface by the Mo-oxide phase and appear to depend on the gas atmosphere (wet or dry 02) during heat treatments in case of solid/solid wetting method. ESR, oxygen and carbon dioxide uptakes and the catalytic properties clearly demonstrate that spontaneous spreading of MoO3 on the AI203 support at 500°C in the presence of wet 02 is a most effective alternative method for preparing molybdena-alumina catalysts.