Decomposition of H₂O₂ on Pure and ZnO-Treated Co₃O₄/Al₂O₃ Solids

Abstract

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 400-600ºC. 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 400ºC 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 400-600ºC. 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 surface 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 400-600ºC of Co 3 O 4 /Al 2 O 3 solids subjected to ZnO treatment did not modify the mechanism whereby the catalytically active constituents (surface cobalt species) were involved in the reaction although their concentration was altered without affecting their energetic nature.

Effect of ZnO doping on surface and catalytic properties of NiO and Co3O4 solids

“…Most of these catalysts have been prepared from noble metals, gold, palladium, and platinum supported on convenient oxides such as ferric oxide, aluminum oxide, stannic oxide, ceria, zirconia, and coblatic oxide [7][8][9][10][11][12]. However, metal -support interactions may take place during the operation of supported catalysts as in the case of Co 3 O 4 /Al 2 O 3 system where the solid -solid interaction between cobalt and aluminum oxides leads to the formation of CoAl 2 O 4 [13]. It is known that the activity and selectivity of a large variety of catalysts can be modified by different methods such as loading on a finely divided support [14 -23] and doping with certain foreign oxides [24 -26], Li 2 O doping of Co 3 O 4 was found to greatly increase (about 10-fold) their catalytic activities in decomposition of H 2 O 2 [27].…”

Influence of ZnO doping and calcination temperature of nanosized CuO/MgO system on the dehydrogenation reactions of methanol

“…1 and 2. The values of crystallite sizes of different phases were calculated using Scherrer equation [25], are given in These obtained results can be explained in the role of ZnO-doping in increasing the degree of dispersion of active phase [26,27] via decreasing its crystallite sizes. The mechanism of this action had been tentatively attributed to coating the copper oxide crystallites by ZnO film that may hinder the particle adhesion of the doped oxide solids [26].…”

Dehydrogenation Reactions of Methanol in Presence of Nanosized-ZnO/CuO/MgO System<strong> </strong>

“…The crystallite size of the phases present was calculated using Scherer equation [23]. These obtained results can be explained in the role of ZnO-doping in increasing the degree of dispersion of active phase [24,25] via decreasing its crystallite sizes.…”