Effect of Ni and Fe Doping Levels on the Nano Core–Shell Structure La₂Ni_2–<i>x</i>Fe_<i>x</i>O₆@CeO₂ Double Perovskite Type Composite Catalysts for Dry Reforming of Methane Performance

Dry reforming of methane (DRM) used two greenhouse gases (CO₂ and CH₄) as reactants to produce hydrogen and syngas, which is considered to be an effective means to address the greenhouse effect. In this paper, a series of nano core-shell structure La₂Ni_2-<i>x</i>Fe_<i>x</i>O₆@CeO₂ composite catalysts with Ni and Fe double regulation at the B-site were prepared by the sol-gel method and applied to the DRM reaction. The experimental results showed that the addition of the Ni ion at the B position of double perovskite can boost the active sites on the prepared catalyst surface and thereby promote the activation and decomposition of reactants. Simultaneously, the incorporation of Fe ions can also increase the lattice oxygen migration and internal oxygen vacancy concentration of the perovskite, and the La₂Ni_1.6Fe_0.4O₆@CeO₂ sample has the highest surface chemisorbed oxygen content (53.37%). Moreover, the strong interaction between the La₂Ni_2-<i>x</i>Fe_<i>x</i>O₆ core and the CeO₂ shell can enlarge the specific surface area and pore volume, which could further improve the oxygen vacancy concentration and coke resistance ability and thus may stimulate the adsorption and dissociation of CH₄ and CO₂. Meanwhile, the suitable doping ratio of Ni and Fe can effectively enhance the redox performance of the catalyst, and the synergistic effect between Ni and Fe can markedly improve its thermal stability and carbon resistance. The density functional theory was employed to reveal the CH₄ adsorption kinetics, and the calculation results convinced us that the La₂Ni_1.6Fe_0.4O₆@CeO₂ catalyst possessed a lower energy barrier and carbon elimination effect in DRM as expected. Moreover, a fixed-bed tubular reactor was employed to evaluate the catalytic performance of the as-prepared samples, and the 6 h experiment results indicate that the La₂Ni_1.6Fe_0.4O₆@CeO₂ catalyst achieves top reaction performance with the desired H₂/CO of 1, with conversions of CH₄ and CO₂ reaching 93.12% and 89.95%, respectively. Finally, 41 h continuous stability experiments exhibit a slight decrease of CH₄ and CO₂ conversions (average: 89.25% and 84.37%), and the average H₂/CO ratio still remained at 1.01.