Exsolution-Mediated <i>In Situ</i> NiCuFeAlloying in Chemically Tailored Hercynite: A Key to Coke-free DryReforming of Methane

We have explored in this work the effect of chemical tailoring through simultaneous doping of Ni and Cu in a hercynite system for the dry reforming of methane (DRM). A series of nanodimensional (10–14 nm) hercynites have been prepared following solution combustion synthesis. The optimized sample, Ni_0.08Cu_0.07Fe_0.85Al₂O₄, is reported to exhibit noteworthy coke-free conversions of 97% and 99% for CH₄ and CO₂, respectively, with a H₂/CO ratio of ∼0.8 at GHSV of 34000 mL g^–1 h^–1 and at ∼800 °C. This investigation highlights the structural evolution of the hercynite-based catalyst with time on stream activity behavior. Characterization of the aged vs the as-prepared catalyst suggests <i>in situ</i> exsolution of the doped metal ions (Ni and Cu) together with a certain portion of Fe from the catalyst leading to formation of NiCuFe trimetallic alloy accompanied by the formation of γ-Al₂O₃ along with the retention of a pristine hercynite phase. Alloying of the active component Ni with Cu and Fe in the presence of the spinels (FeAl₂O₄ and γ-Al₂O₃) is shown to be beneficial in circumventing the difficulties of Ni-only catalysts in DRM. Interestingly, the residual carbon, present initially in the combustion-synthesized catalyst, gets diminished in the course of the reaction, suggesting Ni_0.08Cu_0.07Fe_0.85Al₂O₄ as a promising catalyst for dry reforming of methane with a sustainable coke-resistant ability.