On the role of Fe³⁺ ions in Fe_xO_y/C catalysts for hydrogen production from the photodehydrogenation of ethanol

Fe_xO_y/C photocatalysts at different iron content were prepared by the incipient wet impregnation method and calcined at 773K. The photocatalysts were characterized by means of nitrogen adsorption-desorption isotherms, surface fractal dimension, non-local density functional theory, X-ray diffraction, Rietveld refinement and UV-vis spectroscopy. The photocatalytic activity was evaluated using the photodehydrogenation of ethanol as a model reaction for the production of hydrogen. The specific surface areas of Fe_xO_y/C substrates, with 15, 20 and 30wt% iron content, diminished from 638 to 490m²/g, as the iron content increased. X-ray diffraction analysis showed that iron oxides coexist as wustite and magnetite in samples with Fe contents of 15 and 20wt%; for sample with 30wt% Fe, wustite, magnetite and hematite phases were observed. The photophysical, textural and structural properties were modified by the hematite phase formed by thermal treatment. The Rietveld refinements denoted changes in occupancy of Fe³⁺ and Fe²⁺ in Fe_xO_y crystallites. A relationship between the Fe³⁺ ions content and the reactivity for the hydrogen production from the photodehydrogenation of ethanol (from 1360 to 2125μmolh^-1), was evidenced.