In situ XAS and NAPXPS investigation of the structural evolution of NiCo particles during Dry and Steam Reforming of Methane

Catalysts based on nickel and/or cobalt supported on lanthanum oxide were examined under in situ conditions using X-ray absorption spectroscopy (XAS) and near-ambient pressure X-ray photoelectron spectroscopy (NAPXPS), with a focus on their performance in methane reforming. These catalysts were synthesized using a method known as “Solid Phase Crystallization” (SPC), where the precursor is LaNi 1-x Co x O 3 with a perovskite structure. This structure presents a general formula ABO 3 , and, in our systems, Ni and Co are uniformly embedded within the perovskite lattice in the B position. Upon reduction, the perovskite-based system transforms into an active catalytic phase, Ni 1-x Co x /La 2 O 3 , which can revert to the original perovskite phase upon high-temperature oxidation. The perovskite-type oxides exhibit remarkable regenerating properties that can be exploited for catalytic applications. This cycle of reduction and re-oxidation points to an inherent regeneration mechanism of the catalyst, driven by reversible modifications in the B-site metal centers. The in situ analysis revealed the formation of NiCo particles after reduction, where nickel appears to play a protective role by shielding cobalt from oxidation. This effect does not translate into significant enhancements in catalytic efficiency, with the bimetallic material displaying performance that lies between that of the individual Ni/La 2 O 3 and Co/La 2 O 3 . NAPXPS measurements under reducing environments, combined with post-reduction STEM observations, indicate the presence of two distinct types of NiCo nanostructures. One exhibits a uniform NiCo alloy intimately mixed with the La 2 O 3 support. The other shows a core-shell like configuration, characterized by cobalt enrichment at the core and nickel predominance at the surface (Co@Ni), both components being partially covered by lanthanum oxide.