Effect of AlO and MoO Doping of CoO Solid on its Surface and Catalytic Properties

• Main Authors: Gamil A. El-Shobaky, Abd. El-Mohsen M. Turky
• Format: Article
• Language: English
• Published: Hindawi - SAGE Publishing 1999-07-01
• Series: Adsorption Science & Technology
• Online Access: https://doi.org/10.1177/026361749901700706

Pure and doped Co 3 O 4 samples were prepared by thermal decomposition at 500–1000°C of pure basic cobalt carbonate and of the basic carbonate treated with aluminium nitrate and ammonium molybdate. The amounts of dopants added were varied within the range 0.75–6 mol% Al 2 O 3 , and 0.025–6 mol% MoO 3 . The influence of this treatment on the specific surface areas and catalytic activities of the Co 3 O 4 solids was investigated using nitrogen adsorption at −196°C and studies of the decomposition of H 2 O 2 at 30–50°C. The results obtained revealed that doping of cobaltic oxide solids with either Al 2 O 3 or MoO 3 , followed by calcination at 500°C and 700°C, resulted in a progressive increase in the BET surface areas. This increase was, however, more pronounced in the case of MoO 3 doping. Calcination of the doped solids at 900°C led to an increase in the BET surface areas of the Al 2 O 3 -treated solids and to a small decrease in the specific surface areas of the MoO 3 -doped samples. Calcination of the variously doped solids at 500–900°C brought about a decrease in their catalytic activity to an extent proportional to the amount of dopant added. Thus, treatment of Co 3 O 4 solids with 6 mol% Al 2 O 3 followed by calcination at 500°C, 700°C and 900°C effected a decrease of 36.9, 42.8 and 67.5% in their activities (expressed as reaction rate constant per unit area) measured at 30°C. The decrease in the catalytic activity of Co 3 O 4 solids due to MoO 3 doping was greater than that effected by Al 2 O 3 doping. The doping process did not change the mechanism of the catalytic reaction but effectively decreased the concentration of CO 3+ –CO 2+ ion pairs acting as the active sites involved in the catalytic process.