Syngas is vital for sustainable energy conversion, but conventional steam-carbon reforming suffers from slow heat transfer and temperature gradients, which promote secondary oxidation and water-gas shift reactions, leading to CO2 formation. Here, a variable-frequency microwave approach was applied using lignin charcoal (LC) as the receptor. Among four tested frequencies, 5525 MHz performed best, reaching 814 degrees C within 80 s at 100 W, with uniform heating and producing CO2-free syngas. Simulations show that 5525 MHz provides superior electric field symmetry, dielectric loss density, and energy utilization efficiency. Spent LC analysis reveals enhanced defects and polarization, sustaining strong microwave absorption. These findings highlight the decisive role of microwave frequency in controlling temperature, energy distribution, and syngas selectivity, offering a prom-ising strategy for low-carbon syngas production.