Semester

Fall

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Edwin L. Kugler.

Abstract

A characterization study was performed on two series of hexaaluminate catalysts of the form MI(MII)xAl12-x O19-delta; where MI refers to the mirror cation (MI = Ba, Sr, La) and MII to the cation (MII = Ni) substituted into the lattice. The first series was synthesized for comparison of different mirror cations while holding the Ni substitution level constant at x = 0.4. The second series was developed with the same mirror cation of Ba, but varied x, the level of Ni substitution. Experiments were conducted by means of the following characterization techniques: scanning electron microscopy (SEM), unit-cell refinement (UCR), in situ temperature-programmed reduction and X-ray diffraction (TPR-XRD) and Fourier-transform infrared (FT-IR) spectroscopy.;UCR showed that Ni has been incorporated into the hexaaluminate lattice during synthesis. Increasing the Ni substitution level results in an increase in the a and b parameters and a decrease in the c direction. The overall volume of the unit-cell was found to increase with higher Ni substitution level. In situ TPR-XRD studies with La and Sr hexaaluminates have shown that Ni in the lattice upon reduction with H2 turns into metallic Ni0 on the hexaaluminate surface of the crystal. Experiments with Ba hexaaluminates were mostly inconclusive due to the hexaaluminate diffraction pattern having intense peaks in the same positions as Ni0 metal so that the hexaaluminate pattern masks the appearance of Ni0 metal peaks. Fourier-transform infrared spectroscopy of the absorption of CO on reduced catalysts was performed to distinguish between Ni+2 ions and Ni0 metal species on the hexaaluminate surfaces. However, the analysis of the FT-IR spectra provided no evidence for CO adsorbed on either Ni+2 ions or metallic Ni0 on the hexaaluminate surface. During exposure of CO, there was the appearance of multiple peaks that indicate the presence of gas phase CO and CO2 molecules as well as the formation of carboxylates and carbonates. Upon evacuation of the experimental chamber, the only remaining peaks belonged to those of the appropriate mirror cation carbonate.

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