Evaluation of Properties Changes by the Addition of Surfactant in the Synthesis of Ni/CeO2

Abstract

This work evaluates how adding cetyltrimethylammonium bromide (CTAB) in the synthesis affects the physical and chemical features of Ni/CeO2 catalysts. The samples were characterized by the Rietveld refinement from X-ray diffraction (XRD) and showed a decrease in the crystallite size and an increase in the microstrain from 5.9 to 7.5 x 10-3. Nitrogen physisorption analysis was used to obtain the pore size distribution by the BJH method, varying the pore size between 8 and 12 nm. Raman spectroscopy was employed to confirm the fluorite structure arrangement of ceria and the number of vacancies in the bulk phase, where the ratio from vibrational modes related to defects and oxygen vacancies increased from 0.488 to 0.516 ratio. With the spectra obtained from X-ray photoelectron spectroscopy (XPS), it was possible to observe the distribution of metals on the surface of the samples and their oxidative states, providing clues about the quantity of vacancies. Samples with higher concentrations of CTAB obtained higher values of Ce3+, reaching a 0.45 ratio on the surface. The scanning electron microscopy (SEM) analysis showed that the addition of CTAB formed more irregular shape grains, reaching 20 μm of medium size for all the samples.

Keywords

• Sol-gel synthesis
• Nickel catalysts
• CeO2 support
• Oxygen vacancy
• Crystal defects