Microwave Synthesis and Characterization of Transition or Rare Earth-Metal Doped Ceria Catalysts for CO Oxidation Applications

  • Alia Almutawa

Student thesis: Master's Thesis

Abstract

Proton Exchange Membrane Fuel Cells (PEMFC) are considered attractive green technology for energy generation due to their zero emissions. Hydrogen -fuel- production through hydrocarbon combustion is known to be the most efficient process, however it feeds the fuel stream with CO impurity at about 2 vol.% that is enough to poison the noble metal catalyst electrode (i.e. Pt) and reduce the overall cell efficiency. To optimize the fuel cell performance, CO impurity has to be reduced to< 10 ppm. Among various CO clean-up approaches, preferential CO oxidation using ceria as heterogeneous catalyst is very promising due to its high selectivity and low cost. In this study, transition metals (i.e. M= Cu, Co, Mn, Fe, Ni, Zr or Zn) or earth-metals (N= La or Gd) were supported on ceria using microwave assisted sol-gel synthesis to improve the thermal stability and ionic conductivity of the catalyst. The effect of the dopants on the variations in the physiochemical properties of Ce0.8 M0.2Ox, and Ce0.8 X0.2Ox catalysts were investigated. The physical and chemical properties of Ce0.8 M0.2Ox were correlated to their CO oxidation performance. The crystallites structures of the binary oxides were revealed by X-ray Diffraction (XRD), the morphological information were obtained by Scanning Electron Microscopy (SEM) and Brunauer -Emmett-Teller (BET) method. The average crystallite sizes ranged between 9-16 nm by Scherrer's equation, where dopant type played significant role in the size variations. Moreover, surface elemental analysis were performed by X-ray Photoelectron Spectroscopy (XPS). The reducibility of the mixed oxides was evaluated by temperature-programmed reduction in H2 atmosphere (H2-TPR) and the acidity was studied by temperature-programmed desorption (CO2-TPD). Variations in surface composition and oxidation states were correlated to the binary oxides reducibility, basicity and catalytic performance. Through CO oxidation activity studies for Ce0.8M0.2Ox, it was found that the catalytic behavior is optimized with copper doping. Finally, CO2 presence effect on the CO conversion of Ce0.8 M0.2Ox (i.e. M=Cu, and Zn) was investigated, where the overall activity was reduced for all of the materials. Indexing Terms: fuel cells, binary mixed metal oxides, ceria, transition metal, microwave, CO oxidation.
Date of AwardNov 2017
Original languageAmerican English
SupervisorKyriaki Polychronopoulou (Supervisor)

Keywords

  • Fuel Cells
  • Binary Mixed Metal Oxides
  • Ceria
  • Transition Metal
  • Microwave
  • CO oxidation.

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