(146k) Flame Synthesis of Nanostructured Sorbents for Desulfurization in Fuel Cells

Natural gas produced from petroleum can be reformed to produce hydrogen. During the reforming process hydrogen sulfide (H2 S) and sulfur dioxide (SO2) poison the steam reforming catalysts and are released into the atmosphere. The presence of these sulfur compounds in the raw materials shortens the reforming process. These compounds are removed at high temperatures (600-800oC) through the process of desulfurization. However, desulphurization technology is most efficient when it is applied with sorbents, which can effectively remove sulfur compounds like H2S and SO2.

In the present study, high surface area sorbents for desulfurization are produced using the flame spray pyrolysis (FSP) method. The flame synthesis process offers a single step method for preparation of these oxides while retaining good particle qualities. The process involves the atomization of precursor solutions, here metal acetates and nitrates, which are then passed over a methane, oxygen and nitrogen flame and then collected by thermophoresis. The sorbents produced are mixed oxides, and include CuFe2O4, CuAl2O4, CuCr2O4, CuO/CeO2. Mixed oxides such as CuFe2O4, CuAl2O4, and CuCr2O4 in the spinel phase (AB2O4) have higher sulfur removal efficiencies because the reduction of Cu to Cu metal is these oxides is much slower (copper is retained in the Cu2+ and Cu1+ oxidation states) than in single oxides. CuO/CeO2 does not form the spinel structure but CeO2 retains Cu in its cluster, preventing its reduction to a metal state. The particles produced using FSP are characterized using thermogravimetric analysis (TGA) to determine the impurities in the particles, X-ray diffraction (XRD) for phase analysis and crystal structure determination, BET gas absorption surface area to determine the surface area and transmission electron microscopy (TEM) for particle size morphology and of the material. The surface area of the particles produced ranged from 38 ? 157m2/g. XRD analysis of the particles indicated the formation of the fluorite phase of CeO2, for the CuO/CeO2 particles, with no indication of the formation of a separate copper oxide phase. XRD analysis of the particles shows the formation of spinel pahs with the presence of individual oxides. Pure spinel phase of these materials can be obtained by heat treatment.