Chapters authored
Cobalt-Based Catalysts for CO Preferential Oxidation
In this work, catalysts based on cobalt supported on ZrO2 and CeO2 and CoCeMnOx were studied for the CO preferential oxidation (COPrOx) in hydrogen-rich stream able to feed fuel cells. Among them, the CoCeMnOx formulation showed the highest CO conversion at low temperatures, while the cobalt oxide supported on ceria presented the best selectivity toward CO2. The Co3O4 spinel was the active phase for the CO preferential oxidation detected in all catalysts. However, the CoOx-CeO2 and CoCeMnOx catalysts resulted more active than cobalt oxide supported on zirconia. The presence of ceria close to cobalt species promotes the redox properties and enhances the catalytic activity. In the CoCeMnOx catalyst prepared by coprecipitation, the incorporation of Mn represented an additional positive effect. The presence of Mn promoted the reoxidation of Co2+ to Co3+ and, consequently, the activity increased at low temperature. By X-ray diffraction (XRD) of CoOx-ZrO2 and the CoOx-CeO2 catalysts, the Co3O4 spinel and ZrO2 or CeO2 were identified in agreement with laser-Raman spectra. At the same time, the CoCeMnOx catalyst, prepared by coprecipitation of precursor salts, showed an incipient development of a new phase (Mn,Co)3O4 mixed spinel, due to the intimate contact between elements.
Part of the book: Cobalt Compounds and Applications
Synthesis of Supported Mesoporous Catalysts Using Supercritical CO2
Metal and metal oxide nanoparticles have attracted increased attention due to their unusual physical and chemical properties. The nature, dispersion, and size of the nanoparticles are key factors in determining the activity and selectivity of the supported catalysts. Supercritical fluid deposition (SCFD) is a promising method to deposit metallic nanoparticles and films on inorganic porous supports. CO2 is the most commonly used supercritical fluid (sc-CO2) for material synthesis because it is nontoxic, nonreactive, nonflammable, and inexpensive. This work presents the synthesis of cobalt, nickel, and ruthenium nanoparticles on MCM-41, Al-MCM-41, MCM-48, and activated carbon supports in sc-CO2. Batch and continuous deposition are studied, with two high-pressure reactor configurations: column or alternative (sandwich). To avoid the length of the bed being too long, the reagents were separated into smaller amounts and placed alternately, keeping the total mass of the precursor and support constant. The prepared samples were characterized by scanning electron (SEM/EDX) and transmission electron microscopy (TEM).
Part of the book: Advances in Microporous and Mesoporous Materials