Effect of additives on the reduction behaviour and CO2 catalytic decomposition of nanocrystallite Fe2O3

Abstract

Compacts of pure Fe2O3 mixed with 5 wt-%MgO, CuO, SiO2 or TiO2 separately, were sintered at 500°C for 1 h and then isothermally reduced with H2 at 500°C to metallic iron. The oxygen weight loss resulting from Fe2O3–Fe reduction steps were continuously recorded as a function of time. X-ray analyses, reflected light microscope and scanning electron microscope were used to characterise the fired and reduced compacts. The influence of MgO, CuO, SiO2 and TiO2 on the reduction and CO2 catalytic decomposition behaviour of Fe2O3 was intensively studied. The reduction was correlated to the microstructure of the reduced samples. The results obtained showed that doping of Fe2O3 with these fluxing oxides decreases the reduction of Fe2O3 at 500°C. This was attributed to formation of entrapped lower oxide relics, which hindered gaseous diffusion. On the other hand, for the CO2 catalytic decomposition process, it was found that the rate of reoxidation of samples reduced from pure Fe2O3 is higher than those samples obtained from Fe2O3 doped with CuO, MgO, TiO2 and SiO2 at the initial stage, whereas at the final stages, the rate of reoxidation of reduced pure Fe2O3 is less than that for reduced Fe2O3 doped with CuO, MgO, TiO2 and SiO2.