Cordierite as catalyst support for cobalt and manganese oxides in oxidation-reduction reactions

Abstract

Cobalt and manganese oxide samples supported on cordierite (commercial grade) were prepared by wet impregnation method using finely powdered support material and cobalt or manganese nitrate. The extent of loading was varied between 5 and 20 wt.% Co3O4 or Mn2O3. The physicochemical, surface and catalytic properties of the thermally treated solids (350 and 700°C) were investigated using XRD, EDX, nitrogen adsorption at -196°C, CO-oxidation by O2 at 225-275°C and H2 O2-decomposition in a aqueous solution at 30-50°C. The results obtained revealed that the employed cordierite preheated at 350-700°C was orthorhombic well crystallized magnesium aluminum silicate (Mg2Al4Si5O18). The manganese oxide-containing cordierite samples consisted of manganese oxide-cordierite solid solution. While all diffraction peaks of Co3O4 were observed in the diffractograms of cobalt-containing cordierite preheated at the same temperatures. The specific surface area of cordierite supportmaterial increases progressively by increasing the amount of manganese or cobalt oxide present. The catalytic activity of cordierite was found to increase almost linearly by increasing the amount of cobalt or manganese oxide added. Cobalt oxide-containing catalysts calcined at 350-700°C exhibited catalytic activity in CO-oxidation by O2 higher than those measured for manganese oxide-containing catalysts calcined at the same temperatures. Opposite results have been observed in the case of H2O2-decomposition. These findings indicate that the active sites taking part in CO-oxidation by O2 are different from those involved in H2O2 -decomposition. © 2004 Elsevier B.V. All rights reserved.