Effect of calcination temperature and MoO3-doping of CO3O4/Al2O3 system on its surface and catalytic properties

The effect of MoO3-doping (0.5-7.5 mol%) of Co3O4/Al2O3 system on its surface and catalytic properties were investigated. The extent of cobalt oxide was fixed at about 16.6 mol%, and the pure and doped solids were heated at 400 and 600 degreesC. The techniques employed were XRD, N-2 adsorption at - 196 degreesC and catalytic decomposition of H2O2 at 20-50 degreesC. The results revealed that most of the dopant added was retained on the uppermost surface layers on the treated samples precalcined at 600 degreesC. The doping process resulted in a limited modification in the surface characteristics for the treated solids. The addition of 2 mol% MoO3 to the investigated system led to a considerable increase in the catalytic activity by three- and five fold for the solids calcined at 400 and 600 degreesC, respectively. However, the addition of further amounts of dopant resulted in a progressive measurable decrease in the catalytic activity due to an effective conversion of some of surface Co3O4 into cobalt molybdate. The considerable increase in the catalytic activity due to treatment with 2 mol% MoO3 could result from creation of new ion pairs and also to an effective increase in the surface concentration of cobalt species. The doping process did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active sites without changing their energetic nature. (C) 2002 Elsevier Science B.V. All rights reserved.