Unravelling the effectiveness of the small partial substitution of Fe by Ni in La0.9Sr0.1Fe1-xNixO3 perovskites to improve their performance in dry reforming of methane

Abstract

Despite the potential of dry reforming of methane (DRM) to valorize CH4 and CO2 into syngas, it must face the rapid catalyst deactivation and competition between reactions that reduce the H2/CO ratio below 1. Perovskitebased catalysts are promising due to their high thermal stability and high oxygen mobility that reduce deactivation by carbon deposition. This work demonstrates the beneficial effect of partially substituting Fe (from 1 to 10 % mol) by Ni in La0.9Sr0.1FeO3 perovskite. For that purpose, an extensive study combining multiple activity tests, characterization of the perovskites and determination of reaction extents by linear programming (LP) optimization was performed. Cofeeding CH4 and CO2 was very effective to keep the perovskite stable while it was severely damaged when feeding only CH4. The perovskite with 5 % Fe substitution (La0.9Sr0.1Fe0.95Ni0.05O3) exhibited the best performance, with CH4 and CO2 conversions of 90 and 95 %, respectively, and H2/CO of 1.1. XPS analysis revealed larger amount of oxygen vacancies than in the Ni-free perovskite. SEM analysis after reaction showed Ni nanoparticles ex-soluted on the perovskite surface. Therefore, the enhanced activity was attributed to a higher oxygen mobility and the role of Ni as DRM catalyst. Analysis of the reaction extents by LP optimization at different reaction conditions revealed changes in the reaction pathways that favored higher H2 yield. XRD, XPS and TG/DTG/DSC of the 5 % Ni-perovskite throughout reaction time showed the progressive appearance of new phases, the generation of more Fe3+ species and oxygen vacancies, and higher coke deposition. Finally, a great stability of the La0.9Sr0.1Fe0.95Ni0.05O3 perovskite was attained when applied in chemical looping dry reforming mode as demonstrated running 50 cycles of alternative DRM and CO2-regeneration steps.