Reshaping interfacial heat supply in the Boudouard reaction through variable-frequency microwave fields

Syngas is a key platform for fuels and chemicals, yet efficient CO₂-to-CO conversion in endothermic Boudouard reactions (C + CO₂ → 2 CO) is limited by nonuniform and delayed interfacial heat supply under conventional heating. To overcome this limitation, a variable-frequency microwave (VFM) strategy is proposed to enable precise interfacial energy delivery and mitigate transient heat deficits. Experiments combined with multiphysics simulations demonstrate that microwave frequency governs electric-field localization and the depth of energy deposition, thereby regulating the dynamics of interfacial heat compensation. Compared with conventional 2450 MHz microwave systems (0-0.2 °C/W), VFM achieves up to 7.1 °C/W (>35-fold enhancement), and an energy-specific CO yield of 8.3 mg/kJ, nearly an order of magnitude higher than electrical heating. Under optimized frequency conditions, strong field-material coupling sustains a surface temperature of 897 °C, enabling 99.8% CO₂ conversion and a CO production rate of 3.0 g/h, far exceeding electrical heating at the same bulk temperature (0.5 g/h, 15.5%). A multi-source entropy decomposition framework is established to quantify conductive, electromagnetic, chemical, and interfacial entropy generation. The results demonstrate the highest interfacial entropy generation and heat replenishment capacity, markedly surpassing other microwave frequencies and conventional electrical heating. Such rapid and localized heat compensation, arising from frequency-matched coupling between electromagnetic field and dielectric responses of the carbon matrix, stabilizes endothermic reaction interface and sustains high CO yields, while effectively lowering the apparent activation barrier (18.0 kJ/mol). Overall, these findings establish a physically grounded framework for tuning interfacial energy delivery in strongly endothermic systems.