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

• Dry reforming of methane on a Rh-doped pyrochlore is described using DFT methods.
• Rh plays a key role in the rate limiting CHO dehydrogenation reaction step.
• The (1 1 1) plane was found to be most energetically favorable for DRM reactions.
• Computed species adsorption and DRM reaction behavior agree with experiments.
• Modeled DRM and reverse water gas shift behavior matches experimental observations.

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.

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