(626f) Optimization of Metal Dopants in Pyrochlore Catalysts for the Dry Reforming of Methane: Combining Computational and Experimental Methods

The advent of advanced drilling technologies has significantly increased methane production rates world-wide, and further increases are possible if cost effective technologies can be developed to remove or make use of the CO₂ species present in many untapped natural gas deposits. Therefore, the dry reforming of methane (DRM) has received special attention as it provides a route for the production of fuels and chemicals via syngas, by employing methane and CO₂ as feedstocks. The trial and error optimization of catalysts for DRM has thus far yielded a modicum of promising catalysts. For example, Rhodium-substituted lanthanum zirconate pyrochlores (LRhZ) have been shown to exhibit high catalytic activity and long-term thermal stability for DRM. To further develop lower cost DRM pyrochlore catalysts with even greater catalyst lifetimes, an in silico optimization study was undertaken that built upon our previous density functional theory and microkinetic modeling studies of Rh-doped pyrochlore catalysts. Computational analysis of one of the rate determining steps (the CHO dehydrogenation reaction, which lies on the favored CH₄ dehydrogenation pathway) suggested Pd as an effective co-dopant to reduce the activation barrier for this step. Thus, a bimettalic Rh-Pd co-doped lanthanum zirconate pyrochlore (Rh-Pd-LZ) was synthesized, characterized, and tested for DRM activity. The Rh-Pd-LZ catalyst exhibited high activity for DRM and H₂ to CO product ratios close to unity at both moderate and high temperatures, which evidences the fostering of DRM and inhibition of the undesired reverse water gas shift reaction (RWGS, CO₂ + H₂ â?? CO + H₂O).