Dry Reforming of Methane Using Rh Substituted Pyrochlores

Dry (CO₂) reforming of methane (DRM) to syngas (H₂ and CO) has been well-studied over a number of catalysts. The high temperatures needed to produce syngas inevitably result in carbon formation. Although pyrochlores are known to be thermally stable at conditions required for dry reforming, we are aware of only one reference in which DRM has been studied (Ashcroft et al., 1993) over pyrochlores. The potential for substituted pyrochlores to exhibit both thermally stability and to resist carbon formation due to their inherent oxygen conductivity suggest that they may be active and stable for DRM. Here, we report the use of Rh-substituted- lanthanum zirconate (La₂Zr₂O₇) pyrochlores for DRM. Isomorphic substitution of Rh as the active metal on the B-site results in an active and stable catalyst for DRM. Specifically three catalysts (a) unsubstituted lanthanum zirconate (LZ) for baseline comparison, (b) 2% and (c) 5% (by wt) Rh-substituted L2RhZ and L5RhZ pyrochlores were characterized using CH₄ and H₂ temperature programmed reduction (TPR) and their activity was studied at different temperatures of 550 ºC, 575 ºC, and 600 ºC. H₂ TPR showed that the reducibility of the pyrochlore increases with an increase in the metal substitution. CH₄ TPR clearly shows that the lattice oxygen in pyrochlores is reactive and helps limit carbon formation. Activity results showed that the CH₄ and CO₂ conversion increase with an increase in metallic substitution into the pyrochlore lattice.