Characterization and Mechanistic Study of Dry Reforming of Methane over Rh Substituted Lanthanum Zirconate (La2Zr2O7) Pyrochlores

Dry 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, there is very little literature on this reaction for these catalysts. Catalytically active metals like Rh and Ru can be isomorphically substituted into the crystalline structure of the pyrochlores to produce stable catalyst. These materials also resist carbon formation due to their inherent oxygen conductivity at conditions required for DRM. Here, we report the use of Rh-substituted- lanthanum zirconate (La₂Zr₂O₇) pyrochlores 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 X-ray diffraction, CH₄ and H₂ temperature programmed reduction (TPR). The most crucial step in DRM mechanism is the activation of CH₄. This step is reported to be the slowest and the rate determining step in the DRM mechanism. In this work we study this CH₄ activation step by means of Arrhenius plot, CH₄/CD₄ kinetic isotope effect.