Surface and Catalytic Properties of Nanocrystalline Pure and Li2O - Doped CoO/Mn2O3 System

Abstract

The effects of calcination temperature (350 - 700°C) and Li2O - doping (0.75 - 4.5 mol%) on solid - solid inter- action, surface and catalytic properties of CoO/Mn2O3 were investigated using XRD, N2 adsorption at -196oC and isopro- panol conversion carried out at 180 - 280°C using a flow method. The results obtained revealed that solid - solid interac- tion between pure and doped - solids took place at temperatures starting from 350°C to yield cobalt manganese oxide (Co, Mn) (Co,Mn)2O4 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. Li2O - doping of the system in- vestigated 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% Li2O in solids calcined at 500 and 700oC, respectively. Li2O - doping exerted an effective increase in total pore volume, the increase reached 57% and 27% by doping with 4.5 mol% Li2O followed 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 calcina- tions 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 cata- lytic activity, measured at 280°C, in presence of 4.5 mol% Li2O 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 Li2O did not change the mechanism of the catalyzed reaction.