When steam is passed over red hot coke, what is produced?

When steam passes over red-hot coke (carbon), the carbon takes the oxygen from the steam:

C + H₂O → CO + H₂

The products are carbon (II) oxide and hydrogen. This mixture is called water gas and is used as a fuel. Carbon (IV) oxide would need more oxygen than the steam supplies at this stage, so it is not the main product.