Promising Combined Pyrochlore-Perovskite Catalysts to Syngas Production

The dry reforming of methane (DRM) is a auspicious process to convert biogas or natural gas into CO + H₂ syngas. The generation of syngas is of great industrial interest in particular in the production of liquid fuels via Fischer-Tropsch. The major problem in DRM is the catalyst deactivation by the formation of carbon deposits over the metal sites. To overcome this problem the catalyst La₂Ce_2-xNi_xO_7-λ-LaNiO₃ was synthesized using coprecipitation (CP) and hydrothermal (HT) methods. These catalysts were characterized and tested catalytically in the DRM at temperatures between 600 to 900°C, and further, tested at 850°C, over 8 hours. The X-ray diffraction analysis showed, in both synthesis methods, the formation of NiO in addition to LaNiO₃ and La₂Ce_2-xNi_xO_7-d. In the temperature programmed reduction analysis, two main reduction peaks characteristic of the perovskite phase were observed with higher reduction temperatures in the HT sample. Furthermore, this catalyst had higher CH₄ and CO₂ conversions at all temperatures, and unlike CP the HT catalyst was active at relatively low temperature of 600°C. In the short term stability at 850°C, the HT catalyst showed very close CH₄ and CO₂ (~90%) conversions suggesting that the reaction is occurring stoichiometrically. In contrast, the CP catalyst showed higher CO₂ (~75%) than CH₄ (~62%) conversion, due the simultaneous occurrence of reverse water gas shift reaction. Regardless of the synthesis method, all catalysts were stable during 8h of time on stream. Furthermore, thermogravimetric analysis after short-term stability tests revealed no significant carbon deposition (<2%). The results indicate that the pyrochlore-perovskite system is active and stable to catalyze the DRM, since it can effectively suppress the deposition of carbon on the surface of the catalyst.