Thermal characterization and catalytic properties of the ZnO-Co3O4/Al2O3 system

The effect of zinc oxide on the thermal and physicochemical properties of the Co3O4/Al2O3 system has been investigated. Different ratios of zinc nitrate solutions were added to mixed ratios of cobalt carbonate and aluminum hydroxide. The thermal decomposition of selected samples was studied by means of thermal analysis (TG and DTG). The pure and doped solids were subjected to thermal treatment at 300-1000 degreesC. The thermal products of all samples were characterized using XRD analysis and IR spectroscopy. The decomposition of hydrogen peroxide was used to measure the catalytic activity of the ZnO-Co3O4/Al2O3 system at 30, 40 and 50 degreesC. The results showed that the thermal treatment of zinc nitrate yielded ZnO at about 255 degreesC. Cobalt carbonate decomposed to Co3O4 and CoO at about 250 and 880 degreesC. CoAl2O4 and ZnAl2O4 were formed as a result of a solid-solid interaction and may form a solid solution of formula Co1-xZnxAl2O4. Both pure ZnO and Al2O3 were inactive with respect to H2O2 decomposition. Pure Co3O4 showed high catalytic activity. The mixed oxides, Co3O4/Al2O3, seem to be more active than pure Co3O4. The addition of a very small amount of ZnO to the Co3O4/Al2O3 system led to an enhancement of its catalytic activity. A further increase in the amount of ZnO led to a sharp decrease in the catalytic activity of the system. (C) 2001 Elsevier Science Ltd. All rights reserved.