Thermal solid–solid interactions and physicochemical properties of Co 3O 4/MoO 3 system treated with Al 2O 3

Abstract

The thermal solid–solid interactions between Co 3O 4 and MoO 3 and their physicochemical properties in the presence and absence of Al 2O 3 have been investigated using thermal analysis (TG–DTG–DTA), X-ray diffraction (XRD) techniques, electron spin resonance (ESR) and catalytic decomposition of H 2O 2 at 30, 40 and 50 °C. The pure and variously doped mixed solids were subjected to heat treatment at 350, 550, 750 and 1000 °C. The amounts of dopant were 1.23, 2.44, 4.76 and 9.09 mol% Al 2O 3. The results revealed that only Co 3O 4 phase was detected for the pure mixed solids calcined at 350, 550 and 750 °C. Doping of the system under investigation with alumina enhanced the formation of crystalline cobalt molybdate phase starting from 350 °C. The degree of crystallinity of CoMoO 4 phase increased with increasing calcination temperature and amount of dopant. Crystalline Al 2(MoO 4) 3 and CoAl 2O 4 phases detected for the solids heavily doped with alumina and calcined at 750 and 1000 °C, respectively as a result of solid–solid interactions between the reacted oxides. CoO phase was detected only for the pure mixed solids and that doped with small amount of alumina and calcined at 1000 °C. The catalytic activity of mixed oxides was higher than that of single oxides obtained at the same temperature. The catalytic activity of Co 3O 4/MoO 3 system progressively decreased with increasing the amount of alumina dopant and with increasing calcination temperature.