CH4 (g) + CO2 (g) → 2 H2 (g) + 2 CO (g)
This is an oxidation-reduction (redox) reaction:
C-IV - 6 e- → CII (oxidation)
CIV + 2 e- → CII (reduction)
4 HI + 4 e- → 4 H0 (reduction)
CH4 is a reducing agent, CO2 is an oxidizing agent, CH4 is an oxidizing agent.