Effects of cobalt loading on the properties of alumina-supported cobalt oxide

Abstract

Recently Arnoldy and Moulijn used a combination of TPR and XRD techniques to study the variation with precalcination temperature of the properties of a reduced 9.1% CoO/Al{sub 2}O{sub 3} catalyst. In their report, cobalt oxides in four kinds of chemical environments, i.e., Co{sub 3}O{sub 4} (reduced around 600 K), a Co{sup 3+} phase on the surface (around 740 K), a Co{sup 2+} phase on the surface (around 875 K), and a CoAl{sub 2}O{sub 4} spinel structure (around 1,160 K) were distinguished from the TPR study. The relative amount of these four phases on the catalysts depended on the temperature of calcination pretreatment. A series of alumina-supported catalysts with various cobalt loadings has been prepared in this laboratory in order to investigate the effect of the metal loading on the relative concentration of the four species described by Arnoldy and Moulijn. The temperature of calcination treatment of the catalysts prepared was fixed at 773 K. The authors intention was to confirm the possible existence of Co{sub 3}O{sub 4} crystallites after the calcination treatment. DRS, XRD, and EPR spectroscopies were coupled to a TPR technique to probe the reduction of these species by the hydrogen.