Ab initio derived reaction mechanism for the dry reforming of methane on Rh doped pyrochlore catalysts

The conversion of methane into syngas is of growing importance given recent increases in methane production worldwide. Furthermore, using CO₂ as the co-feed offers many environmental advantages. To this end, experimentalists have shown that Rh-substituted lanthanum zirconate pyrochlore (LRhZ) catalysts are active and stable at the high temperatures needed for the dry reforming of methane (DRM). To enable further improvements to these catalysts, the reaction mechanism for DRM on LRhZ catalysts was attained using density functional theory (DFT). Following the identification of favored reaction sites for all elementary reactions, reaction and activation energies were calculated and used to discern the primary reaction pathway. Simulations show that inclusion of Rh decreases activation barriers, including the barriers for the two rate limiting steps (CH₂ oxygenation and CHO dehydrogenation), which makes the plane (1 1 1) catalytically active for DRM. The slow steps are on the CH₄ dehydrogenation/oxygenation path, which agrees with experimental observations.