Effect of ZnO doping on surface and catalytic properties of NiO and Co 3O 4 solids

Abstract

The surface and catalytic properties of NiO and Co 3O 4 solids as being influenced by ZnO doping have been investigated. The techniques employed were XRD, nitrogen adsorption at −196 °C, and catalytic oxidation of CO by O 2 at 150–250 °C. The dopant concentration was varied between 2 and 8 wt.% ZnO, and the solids were subjected to heat treatment at 300, 500, and 700 °C. The results obtained revealed that ZnO treatment of NiO and Co 3O 4 followed by calcination at 300 °C resulted in a progressive decrease in their specific surface areas. This treatment brought about an increase in the crystallite size of NiO and Co 3O 4 phases. ZnO doping of Co 3O 4 conducted at 500 and 700 °C effected a progressive increase in its BET surface areas. The calalytic activities towards carbon monoxide oxidation by oxygen expressed as reaction rate constant per unit surface area, k̄, for NiO and Co 3O 4 precalcined at 300 °C were found to increase by ZnO doping. On other hand, doping Co 3O 4 carried out at 500 and 700 °C led to a measurable decrease in its specific catalytic activity ( k̄). The doping process of the investigated solids did not modify the mechanism of the catalyzed reaction but changed the concentration of the catalytically active sites without changing their energetic nature.