Hierarchical core–shell Ni@C-NCNTs nanocomposites tailored for microwave-induced dry reforming of methane process

Abstract

The dry reforming of methane (DRM) is an important technology for syngas production, but its industrial application has been limited by the extremely high temperatures required to activate the thermodynamically stable CH₄ and CO₂ molecules. Herein, Ni-MOF-derived Ni@C-NCNTs nanomaterials with hierarchical core–shell structures and N-doped defects were elaborately designed and synthesized as bifunctional microwave absorbers and reforming catalysts by two-step pyrolysis processes. Efficient syngas production via the microwave-induced DRM (MW-DRM) process over Ni@C-NCNTs-5 was achieved. The double-hierarchical Ni@C-NCNTs with different loading amount of defective N-doped carbon nanotubes (NCNTs) on the Ni@C microstructures were rationally constructed by modulating the dosage of melamine in the secondary pyrolysis processes, which significantly improved the microwave absorption and conversion capacity and catalytic performance due to the synergistic effect of multiple loss mechanism of the incident microwave and the mitigation of active metal sintering. Density functional theory (DFT) calculations also indicated that surface engineering on the defects of the Ni@C-NCNTs catalysts could strongly promote the electron transfer and thus enhance the adsorption and catalytic activation of CH₄ and CO₂. More meaningfully, energy efficiency was significantly improved for the MW-DRM process by approximately 31 times than the conventional heating catalytic process owing to the direct, rapid, and highly effective energy transfer process under microwave irradiation. In conclusion, this dimensionally-designed core–shell catalyst demonstrated obvious superiority of catalytic performance and process intensification in the MW-DRM process.