Catalytic partial oxidation of CH4 over Ni-substituted barium hexaaluminate catalysts

Ba0.75NiyAl12−yO19−δ (y = 0.2, 0.4, 0.6, 0.8 and 1.0) catalysts were tested for the partial oxidation of CH4 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 CH4 proceeds at the inlet until all oxygen is reacted, followed by the reaction of CO2 and H2O with unreacted CH4, 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 Ni2+, which has a larger ionic radius than aluminum, substitutes for Al3+ 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.