Dry methane reforming over lanthanide-doped Co–Al catalysts prepared via a solution combustion method†

Cobalt-based catalysts containing Ce, La and Al were prepared via solution combustion synthesis (SCS) and used in dry reforming of methane (DRM). Combustion temperature for the highest active 20Co–10La–20Al catalyst measured during the combustion process was 861 °C, explaining the formation of CoAl₂O₄, which was active for DRM in the present work. No graphite structure was defined from the XRD pattern and TPO profiles of the spent Co–La–Al catalyst, while other catalysts contained this phase. In addition, only 10 wt% of carbon was identified in Co–La–Al, according to CHNS results. All catalysts were well dispersed, and the metal particle size varied between 19 and 28 nm. TPR analyses showed that doping of rare-earth metals leads to easier reduction due to oxygen vacancies, which suppress coking. The highest CH₄ transformation rate and space-time yield of hydrogen were observed for CoLaAl, which exhibited a metal particle size of 23 nm, giving the lowest carbon content in the spent catalysts after temperature cycling experiments in DRM. This catalyst containing metallic cobalt and an active CoAl₂O₄ spinel demonstrated stable formation of hydrogen and CO during 50 h time-on-stream. The spinel phase was, however, decomposed during the DRM. The best catalyst also contained a perovskite-type mixed oxide, LaCo_xAl_1−xO₃, which was already formed during synthesis through an SCS method. This phase was not, however, stable in long-term experiments.