Abstract
Iron oxidic species supported on silica SBA-15 were synthesized with various iron loadings using two different FeIII precursors. The effect of varying powder layer thickness during calcination on structural and solid-state kinetic properties of FexOy/SBA-15 samples was investigated. Calcination was conducted in thin (0.3 cm) or thick (1.3 cm) powder layer. Structural characterization of resulting FexOy/SBA-15 samples was performed by nitrogen physisorption, X-ray diffraction, and DR-UV/Vis spectroscopy. Thick powder layer during calcination induced an increased species size independent of the precursor. However, a significantly more pronounced influence of calcination mode on species size was observed for the FeIII nitrate precursor compared to the FeIII citrate precursor. Temperature-programmed reduction (TPR) experiments revealed distinct differences in reducibility and reduction mechanism dependent on calcination mode. Thick layer calcination of the samples obtained from FeIII nitrate precursor resulted in more pronounced changes in TPR profiles compared to samples obtained from FeIII citrate precursor. TPR traces were analyzed by model-dependent Coats-Redfern method and model-independent Kissinger method. Differences in solid-state kinetic properties of FexOy/SBA-15 samples dependent on powder layer thickness during calcination correlated with differences in iron oxidic species size.