Solid-State Kinetic Investigations of Nonisothermal Reduction of Iron Species Supported on SBA-15

• Published in: Journal of analytical methods in chemistry Vol. 2017; no. 2017; pp. 1 - 13
• Main Authors: Genz, N. S., Ressler, T., Baabe, D.
• Format: Journal Article
• Language: English
• Published: Cairo, Egypt Hindawi Publishing Corporation 01.01.2017; Hindawi; John Wiley & Sons, Inc; Hindawi Limited
• Subjects: Activation energy; Analysis; Catalysis; Chemical synthesis; Chemistry; Comparative analysis; Decomposition; Diffraction; Investigations; Iron oxides; Kinetics; Metal oxides; Methods; Nitrates; Nitrogen; Properties; Reduction; Silicon dioxide; Solid state; Spectrum analysis; Structural analysis; Transmission electron microscopy; X-rays; Germany
• ISSN: 2090-8865; 2090-8873
• DOI: 10.1155/2017/6205297

Iron oxide catalysts supported on nanostructured silica SBA-15 were synthesized with various iron loadings using two different precursors. Structural characterization of the as-prepared FexOy/SBA-15 samples was performed by nitrogen physisorption, X-ray diffraction, DR-UV-Vis spectroscopy, and Mössbauer spectroscopy. An increasing size of the resulting iron species correlated with an increasing iron loading. Significantly smaller iron species were obtained from (Fe(III), NH4)-citrate precursors compared to Fe(III)-nitrate precursors. Moreover, smaller iron species resulted in a smoother surface of the support material. Temperature-programmed reduction (TPR) of the FexOy/SBA-15 samples with H2 revealed better reducibility of the samples originating from Fe(III)-nitrate precursors. Varying the iron loading led to a change in reduction mechanism. TPR traces were analyzed by model-independent Kissinger method, Ozawa, Flynn, and Wall (OFW) method, and model-dependent Coats-Redfern method. JMAK kinetic analysis afforded a one-dimensional reduction process for the FexOy/SBA-15 samples. The Kissinger method yielded the lowest apparent activation energy for the lowest loaded citrate sample (Ea ≈ 39 kJ/mol). Conversely, the lowest loaded nitrate sample possessed the highest apparent activation energy (Ea ≈ 88 kJ/mol). For samples obtained from Fe(III)-nitrate precursors, Ea decreased with increasing iron loading. Apparent activation energies from model-independent analysis methods agreed well with those from model-dependent methods. Nucleation as rate-determining step in the reduction of the iron oxide species was consistent with the Mampel solid-state reaction model.