Applied Catalysis A: General, Vol.323, 1-8, 2007
Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation
Reforming studies were conducted on nickel-substituted hexaaluminate catalysts, ANi(0.4)Al(11.6)O(19-delta) (A = La, Sr and Ba), to reform liquid hydrocarbon fuels into Hz-rich synthesis gas for fuel cell applications. The reaction conditions studied were the partial oxidation of n-tetradecane (I) and n-tetradecane with 50 ppmw sulfur as dibenzothiophene (II). Hexaaluminate catalyst activity toward reaction conditions (I) and (II) as well as the surface Ni concentration and dispersion was shown to correlate with the type of mirror cation substituted into the lattice. The Ni surface concentration was determined by XPS to be 5.3, < 0.1 and 0.7 wt.% for LaNi0.4Al11.6O19-delta, BaNi0.4Al11.6O19-delta and SrNi0.4Al11.6O19-delta, respectively. SrNi0.4Al11.6O19-delta and BaNi0.4Al11.6O19-delta catalysts exhibited stable performance for reaction condition (I), while the loss in activity exhibited overtime by LaNi0.4Al11.6O19-delta suggested site blocking by carbon deposition. Under reaction condition (II), additional activity loss was experienced by both LaNi0.4Al11.6O19-delta and SrNio(0.4)Al(11.6)O(19-delta) catalysts due to the presence of dibenzothiophene. However, LaNi0.4Al11.6O19-delta experienced more severe and partially reversible site blocking where SrNio(0.4)Al(11.6)O(19-delta) experienced a less severe loss of activity, selectivity and irreversible site blocking. The behavior observed in nickel-substituted hexaaluminate catalysts suggests that the different mirror cations influenced the coordination of Ni sites within the lattice and adsorption of hydrocarbons to the surface of the catalysts. Published by Elsevier B.V.