This has been related to the particularly high activity of cobalt in the spinel octahedral site, while cobalt in the tetrahedral site appears much less active. Among these, cobalt-based spinel oxide nanoparticles can be an interesting alternative, taking into account their high activity for CO oxidation. Some noble metals and transition-metal oxides are efficient for the CO-PROX reaction, and the latter, despite their lower general robustness, are mostly preferred mainly for economic reasons. Ideally, CO-PROX catalysts should work at relatively low temperatures (close to that of PEMFC operation), have high CO oxidation activity, and be selective towards CO 2 instead of H 2O (or other products like methane, for instance). The CO-PROX reaction is considered the most effective and economical method to reduce the CO levels to acceptable concentrations.
The latter reaction focuses on the elimination of CO, which is known to deactivate Pt-based electrocatalysts typically employed in PEMFC. The PEMFC operation requires the use of high-purity hydrogen and, for that purpose, the reforming reaction is sequentially followed by the water-gas shift (WGS) and CO preferential oxidation (CO-PROX) catalytic reactions.
Hydrogen can be produced by a number of different processes, but natural gas reforming is by far the dominant technology for production in commercial quantities, while the reforming of hydrocarbons or oxygenated hydrocarbons is also considered most practical for on-board hydrogen production. Among the various types of fuel cells, proton exchange membrane fuel cells (PEMFC), which combine high power density, efficiency, and environmental friendliness, represent the most interesting ones for power generation, particularly for mobile applications. Fuel cell power generation is considered as the most efficient energy technology to produce electricity from chemical fuels. Therefore, the development of new green resources is currently one of the most important and relevant research topics.
In turn, no methanation activity is observed in any case except for the copper-containing catalyst, in which achievement of reduced states of cobalt appears most favored.ĭuring the last years, the global consumption of fossil fuels has increased markedly, leading to environmental problems. cobalt oxidation, induced in CoFe 2O 4 upon introduction of the metals. This is basically attributed to the surface modifications, i.e. It is shown that while the presence of the various metals on CoFe 2O 4 hinders a low temperature CO oxidation process, it appreciably enhances the activity above 125 ☌. The catalysts have been characterized by N 2 adsorption, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR), and X-ray photoelectron spectra (XPS), as well as diffuse reflectance infrared DRIFTS under reaction conditions with the aim of establishing structure/activity relationships for the mentioned catalyst/process. In turn, the promoting effects of incorporation of Ce, Co, Cu, and Zr by impregnation on the surface of CoFe 2O 4 on the process are examined as well. CoFe 2O 4 prepared by sol-gel has been examined with respect to its catalytic performance for preferential CO oxidation in a H 2-rich stream.
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