Novel core–shell NiO@CuFeO2 and NiO@CuFe2O4 nanocatalysts prepared via ultrasound-microwave with high-performance in dry reforming of methane

Abstract

Copper-iron mixed oxides with different Fe/Cu molar ratios, along with NiO, NiO@CuFe₂O₄, and NiO@CuFeO₂ nanocatalysts, were synthesized via hydrothermal treatment assisted by ultrasonic and microwave irradiation. Comprehensive characterization using XRF, N₂ physisorption, XRD, FTIR, H₂-TPR, TGA, and TEM-EDS confirmed the formation of mesoporous materials and well-defined core–shell architectures, consisting of Ni-rich cores encapsulated by CuFe oxide shells. TEM analysis revealed average shell thicknesses of approximately 22 nm for NiO@CuFe₂O₄ and 15 nm for NiO@CuFeO₂. The catalytic performance in the dry reforming of methane (CH₄/CO₂ = 1, atmospheric pressure) showed that bare NiO, although initially highly active, underwent rapid deactivation due to sintering and severe carbon deposition. In contrast, post-reaction analyses demonstrated negligible carbon formation on the NiO@CuFe₂O₄ and NiO@CuFeO₂ catalysts. XRD analysis after reduction evidenced the formation of a Ni-Cu alloy, which modulates the electronic structure and catalytic behavior of Ni. The presence of the Ni-Cu alloy suppresses carbon deposition by reducing the intrinsic tendency of Ni to promote methane cracking, while simultaneously preventing the reoxidation of metallic Ni into inactive NiO species under DRM conditions. Consequently, the strong synergistic interaction between Ni and Cu enhances structural stability, preserves high catalytic activity, and provides excellent resistance to coking.