Application of ZrO₂-Based Hierarchical Nanofibers as a Promoter in Ni Catalyzed Methane Dry Re-Forming

In this work, the use of electrospun zirconia nanofibers (NFs), native and doped with 8% mol yttrium, was evaluated for the first time as supports for Ni-based hierarchical catalysts in the dry re-forming of methane (DRM). By a thermal annealing process of the as-made fibers to 500-1000 °C, we induce controlled changes to the NFs structural properties, before the introduction of a thin MgAlO_x mixed oxide (MO) layer and nickel (Ni) to make hierarchical catalysts for DRM. Analyzing the NFs properties, we find that the grain size of the underlying supports have a strong monotonically increasing correlation to the DRM reaction performance. Specifically, we find that the increase in the ZrO₂ or yttria stabilized zirconia (YSZ) grain size by 2-3 enhances the CH₄ and CO₂ conversions by a factor of 2. We attribute this effect to the efficiency of the contact between the thin MgAlO_x MO layer and the underlying supports, and their joint effect on the Ni-catalyzed DRM. We show that the same enhancement does not occur when using a support material based on ZrO₂ nanoparticles (NPs) rather than NFs. High-resolution transmission electron microscopy shows that the Ni NPs were exsolved from the MgAlO_x MO thin layer to form a coke and sinter-resistant catalyst.