Semester

Spring

Date of Graduation

2007

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Edwin L. Kugler.

Abstract

Studies were conducted on active metals (i.e., Co, Fe and Ni) substituted into the lattice of hexaaluminate compounds to reform liquid hydrocarbon fuels into H2-rich synthesis gas for fuel cell applications. Both the concentration of active metals substituted into the lattice and the different mirror cations, (i.e., Ba, La and Sr) were investigated for their effect on the catalytic properties of the hexaaluminate compound. In these studies, n-tetradecane was used as a model middle distillate fuel. The synthesized catalysts were characterized by a series of techniques including: N2 BET surface area, powder XRD, TPR, H2 pulse chemisorption, bulk elemental analysis by ICP, and surface analysis by XPS.;The catalysts were shown to exhibit P63/mmc crystal symmetry which was indicative of the hexaaluminate structure. TPR experiments on the catalysts indicated that the substitution of cobalt, iron and nickel cations into the lattice stabilized their reducibility. The reduction temperature for the nickel series of catalysts correlated with the type of mirror cation substituted into the lattice. H2 pulse chemisorption performed on reduced nickel hexaaluminate catalysts confirmed that the number of active nickel sites that were reduced in the lattice was influenced by the mirror cation. XPS analysis of LaNi0.4Al11.6O19-delta , SrNi0.4Al11.6O19-delta and BaNi 0.4Al11.6O19-delta catalysts indicated that the variation in the nickel surface concentration of the oxide catalysts also correlated with the mirror cation.;The activity of the synthesized catalysts toward the partial oxidation of n-tetradecane was examined by temperature programmed reaction between 750 to 900°C. Iron substituted into the hexaaluminate lattice was shown to exhibit relatively poor catalytic activity and selectivity at all concentrations during the temperature programmed reaction with n-tetradecane. Cobalt substituted into the hexaaluminate lattice at concentrations of y ≤ 0.8 (LaCo yAl12-yO19-delta) exhibited equally poor catalytic activity and selectivity. However, the LaCoAl11O19-delta catalyst exhibited equilibrium CO and H2 yields.;The LaNiyAl12-yO19-delta (y = 0.2, 0.4, 0.8 and 1.0) series and the MINi0.4Al11.6 O19-delta (MI = Ba, La and Sr) series of catalysts possessed the greatest H2 and CO activity and selectivity over the temperature region examined. Both the LaNi0.2Al11.8O 19-delta and the BaNi0.4Al11.6O19-delta catalysts exhibited sharp increases in H2 yield at 850 and 875°C, respectively. The increase in H2 yield in this region corresponded to a decrease in CH4 yield indicating that the additional H2 produced was derived from CH4.;The role that the mirror cation produced on nickel substituted hexaaluminate stability during n-tetradecane isothermal partial oxidation was also examined. Nickel catalysts with Ba2+ and Sr2+ mirror cations exhibited greater stability during n-tetradecane partial oxidation than did the La3+ cation. The catalytic behavior induced by the mirror cation suggested that its influence on controlling carbon deposition was structural.

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