Al2O3 + 3 C + Cl2 → 2 AlCl + 3 CO
This is an oxidation-reduction (redox) reaction:
3 C0 - 6 e- → 3 CII (oxidation)
2 Cl0 + 2 e- → 2 Cl-I (reduction)
2 AlIII + 4 e- → 2 AlI (reduction)
C is a reducing agent, Cl2 is an oxidizing agent, Al2O3 is an oxidizing agent.