Surface and catalytic properties of nanocrystalline pure and Li <inf>2</inf>O-doped CoO/Mn <inf>2</inf>O <inf>3</inf> system

Abstract

The effects of calcination temperature (350 - 700°C) and Li 2O- doping (0.75 - 4.5 mol%) on solid - solid interaction, surface and catalytic properties of CoO/Mn 2O 3 were investigated using XRD, N 2 adsorption at -196°C and isopropanol conversion carried out at 180 - 280°C using a flow method. The results obtained revealed that solid - solid interaction between pure and doped - solids took place at temperatures starting from 350°C to yield cobalt manganese oxide (Co, Mn) (Co ,Mn) 2O 4 phase. The degree of crystallinity and crystallite size of the produced phase increased progressively as a function of calcination temperature but still remained as nanocrystalline phase 15 - 33 nm. Li 2O- doping of the system investigated decreased the crystallite size of the produced phase. The doping process decreased the specific surface area of the system investigated, the decrease attained 33% and 32% in presence of 4.5 mol% Li 2O in solids calcined at 500 and 700°C, respectively. Li 2O - doping exerted an effective increase in total pore volume, the increase reached 57% and 27% by doping with 4.5 mol% Li 2Ofollowed by calcination at 500 and 700, respectively. Pure system showed a broad pore volume distribution while the doped solids exhibited multimodal pore volume distribution curves. Pure and variously doped solids acted as dehydrogenation catalysts yielding only acetone. The activity increased by increasing the calcinations temperature from 350°C to 400°C, then decreased upon increasing the calcinations temperature above this limit. The doping process carried out at 500°C and 700°C much increased the catalytic activity. The maximum increase in the catalytic activity, measured at 280°C, in presence of 4.5 mol% Li 2O attained 45 and 94% for the solids calcined at 500°C and 700°C, respectively. The increase in calcination temperature within 350°C and 700°C and doping with different amounts of Li 2Odid not change the mechanism of the catalyzed reaction. © El-Shobaky et al.