Thermal decomposition of precursors and iron oxide properties

Abstract

In this work, manganese and copper promoter effect was investigated over iron oxide obtained by thermal decomposition of iron(III) hydroxoacetate (nominal ratio Fe/Mn = 10 and Fe/Cu = 10). The solids were characterized by X-ray fluorescence, thermal analysis (TG, DTG, DTA), Fourier transform infrared spectroscopy (FTIR), physisorption experiments, thermoprogrammed reduction and powder X-ray diffraction. During the precursor thermal decomposition process, the step referred as dehydration/dehydroxylation was controlled by volatile species diffusion. Decomposition stage [Fe(III) to Fe(II) reduction] was controlled by solid geometry and particle size (Coats–Redfern model). FCA-C sample showed Fe(II)/Fe(III) the highest ratio, indicating that through precursor decomposition process reduction is favored. With the use of Ozawa and Kinssinger methods, it became clear that FMCA precursor decomposition showed the lowest activation energy value leading to solid FMCA-C with higher specific surface area and pore volume than the iron oxide-free dopants. The FMCA-C sample reduces hematite to magnetite (low temperature) easily and shows the highest stability of magnetite under reductive conditions.