Synergistic Effect of Nickel and Carbon Defects on Reverse Boudouard Reaction Toward Sustainable Chemical Looping

The integration of catalytic methane decomposition (CMD) with CO₂ gasification (Reverse Boudouard Reaction) offers a promising chemical looping route for carbon-negative hydrogen and syngas production. This work systematically investigates the gasification reactivity of six carbon morphologies, CNTs, CNFs, activated carbon, graphite, graphene, and CMD-derived carbon, with and without Ni addition. First, activity tests and characterization (XRD, XPS, Raman) revealed that CMD-derived carbon outperformed all other benchmarks due to its highly amorphous nature (sp³/sp² = 0.98), which provides a high density of reactive sites. Second, kinetic analysis showed that the incorporation of 5 wt% Ni on CMD carbon reduced the activation energy (E_a) from 435.3 kJ mol⁻¹ to 114.6 kJ/mol, the lowest among all samples. This 74% reduction confirms that structural defects in CMD carbon act as anchoring sites for Ni, facilitating a strong metal–support interaction (MSI) that promotes CO₂ activation. Third, an investigation into structural synergy revealed that higher Ni loadings (>5 wt%) increased the activation energy (up to 171.2 kJ mol⁻¹). This trend is attributed to Ni agglomeration and weakened MSI, which reduces the active catalytic interface. These findings demonstrate that the efficiency of CO₂ valorization is highly sensitive to carbon morphology, providing a clear optimization strategy for integrated chemical looping methane-to-syngas energy cycles.