Dry Reforming of Methane on Rh-Doped Pyrochlore Catalysts: A Steady-State Isotopic Transient Kinetic Study

Increases in worldwide methane production from biological and fossil sources have led to an increased level of interest in the dry reforming of methane (DRM) to produce syngas. Experimental efforts have shown that select pyrochlore materials, such as the Rh-substituted lanthanum zirconate pyrochlore (LRhZ), are catalytically active for DRM, exhibit long-term thermal stability, and resist deactivation. This work seeks to allow further catalyst improvements by elucidating surface reaction kinetics via steady-state isotopic transient kinetic analysis (SSITKA) of dry reforming on the LRhZ pyrochlore. Isotopically labeled CH₄ and CO₂ were used in multiple SSITKA experiments to elucidate the migration of carbon atoms to product species. Short surface residence times at 650 and 800 °C (<0.6 s) were observed for DRM intermediates involved in reversible reactions, and the participation of all surface metal atoms as active sites for DRM, not only Rh, is suggested. Isotopic responses and kinetic isotope effects are explained using reaction mechanism details derived from density functional theory studies of the surface reactions.