Catalytic partial oxidation of CH 4 over Ni-substituted barium hexaaluminate catalysts

Abstract

Ba 0.75Ni y Al 12− y O 19− δ ( y = 0.2, 0.4, 0.6, 0.8 and 1.0) catalysts were tested for the partial oxidation of CH 4 at temperatures between 200 and 900 °C. Temperature programmed reaction results indicate that light-off for the partial oxidation reaction occurred between 665 and 687 °C for all catalysts. Isothermal runs performed at 900 °C on the catalysts showed stable reaction product concentrations, consistent with equilibrium. Post-reaction analysis of the used catalysts showed that there are two distinct zones in the catalyst bed. In a short leading edge of the bed, the apparently complete consumption of oxygen leads to a catalyst which XANES analysis shows is primarily Ni-substituted into the hexaaluminate phase. In the downstream portion of the bed, Ni is shown to be present as metallic Ni. This corresponds to a reaction sequence in which the oxidation of CH 4 proceeds at the inlet until all oxygen is reacted, followed by the reaction of CO 2 and H 2O with unreacted CH 4, and its derivatives, to produce the final syngas mixture. From the change in the unit-cell dimensions with Ni substitution, there is a clear indication that Ni 2+, which has a larger ionic radius than aluminum, substitutes for Al 3+ in the hexaaluminate lattice in the synthesis process, and there is no restructuring of the bulk hexaaluminate phase after the Ni is removed from the lattice.