Hydrogen Production from the Water-Gas Shift Reaction on Iron Oxide Catalysts

Unsupported and supported iron oxide catalysts were prepared by incipient wetness impregnation method and studied in the water-gas shift reaction (WGSR) in the temperature range 350–450°C. The techniques of characterization employed were BET, X-ray diffraction, acid-base measurements by microcalorimetry and in situ diffuse reflectance infrared Fourier transform spectroscopy. MgO, TiO2, or SiO2 was added in order to (i) obtain a catalyst exempt of chromium oxide and (ii) study the effect of their acid-base properties on catalytic activity of Fe2O3. X-ray diffraction studies, and calorimetric and diffuse reflectance infrared Fourier transform measurements reveal a complete change in the physicochemical properties of the iron oxide catalyst after MgO addition due to the formation of the spinel oxide phase. These results could indicate that the MgFe2O4 phase stabilizes the reduced iron phase, preventing its sintering under realistic WGSR conditions (high H2O partial pressures). 1. Introduction Carbon oxide reacts with water and produces, via the reversible and exothermic reaction: , carbon dioxide with pure hydrogen. In recent years, this reaction has received considerable interest due to the possibility to reduce a large amount of carbon monoxide from reformed fuels (CO + H2) into additional hydrogen production. This reaction is catalyzed with a large variety of metals and metal oxides like Fe [1–3], Cu [2, 4], Au [2, 5, 6], Ru [2, 7], and Pt [8, 9] and is often performed in two steps to achieve rates for commercial purposes. At lower temperature (150–250°C) the catalyst of choice is based on copper Cu-ZnO. The iron oxide-based catalysts, Fe2O3, are well known in high temperature water-gas shift reaction (350–450°C) and are generally doped with chromium oxide, Cr2O3, which prevents the sintering of iron oxide crystallites. Before the high temperature shift catalysts can be used, hematite must be converted to magnetite which is believed to be the active phase. This reduction is carried out with process gas mixtures of hydrogen, nitrogen, carbon oxide, carbon dioxide, and water vapour and is controlled to avoid further reduction of magnetite active material to lower oxides or to metallic iron species. Metallic iron is an active catalyst for the methanation of CO and the Fischer-Tropsch processes, which is undesirable here, since all generated hydrogen is consumed. To solve this problem, it is suitable to develop iron oxide stable catalysts that would be more difficult to reduce to metallic iron. Júnior et al. [10] have indicated that the substitution of