Decomposition of H 2 O 2 on Pure and ZnO-treated Co 3 O 4 /Al 2 O 3 Solids

The effects of Co 3 O 4 loading, precalcination temperature and ZnO treatment on the catalytic properties of the Co 3 O 4 /Al 2 O 3 system were investigated. The amounts of Co 3 O 4 were varied between 5.57 wt% and 32.0 wt% and the resulting solids subjected to heat treatment at temperatures in the range 400- 600o C. The amounts of ZnO were varied between 0.36 wt% and 2.12 wt%. The results obtained indicated that ZnO treatment of Co 3 O 4 /Al 2 O 3 solids followed by precalcination at 400o C resulted in a progressive decrease in the particle size of the Co 3 O 4 crystallites in the resulting samples. The catalytic activity of such solids towards H 2 O 2 decomposition decreased progressively as the precalcination temperature employed was increased in the range 400- 600o C. The relationship between the catalytic activity expressed as a plot of the reaction rate constant, k, versus the amount of Co 3 O 4 in the samples showed a progressive increase in the range 5.6- 17.7 wt% followed by an abrupt increase when the extent of loading exceeded this limit. Treatment with ZnO effected a measurable increase (42%) in the specific sur- face area (S BET ) of the treated solids. However, such treatment also resulted in a considerable increase in the value of the reaction rate constant for the catalyzed reaction. Thus, the maximum increase in the value of k 20oC due to doping with 2.12 wt% ZnO attained a value of 543% while the corresponding increase in the value of the reaction rate constant per unit surface area, _ k 20oC , was 331%. Precalcination at 400- 600o C of Co 3 O 4 /Al 2 O 3 solids subjected to ZnO treatment did not modify the mechanism whereby the catalytically active constituents (sur- face cobalt species ) were involved in the reaction although their concentration was altered without affecting their energetic nature.