| Additive or equilibrium reaction | Gas phase composition | |
| CO% | CO2% | |
| None catalyst | 80 | 20 |
| Fe catalyst, 8% | 85 | 15 |
| Cu catalyst, 10% | 82.5 | 17.5 |
| FeO + CO = Fe + CO2 at equilibrium | 74 | 26 |
| CuO + CO = Cu + CO2 at equilibrium | ~10−7 | ~100 |
| CO2 + C = 2CO | ~100 | ~0 |