Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation

Abstract

Abstract Reforming studies were conducted on nickel-substituted hexaaluminate catalysts, ANi 0.4 Al 11.6 O 19− δ (A = La, Sr and Ba), to reform liquid hydrocarbon fuels into H 2 -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, 0.4 Al 11.6 O 19− δ , BaNi 0.4 Al 11.6 O 19− δ and SrNi 0.4 Al 11.6 O 19− δ , respectively. SrNi 0.4 Al 11.6 O 19− δ and BaNi 0.4 Al 11.6 O 19− δ catalysts exhibited stable performance for reaction condition (I), while the loss in activity exhibited over time by LaNi 0.4 Al 11.6 O 19− δ suggested site blocking by carbon deposition. Under reaction condition (II), additional activity loss was experienced by both LaNi 0.4 Al 11.6 O 19− δ and SrNi 0.4 Al 11.6 O 19− δ catalysts due to the presence of dibenzothiophene. However, LaNi 0.4 Al 11.6 O 19− δ experienced more severe and partially reversible site blocking where SrNi 0.4 Al 11.6 O 19− δ 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.