Methane is CH4. Carbon from Carbon Dioxide (CO2) and Hydrogen from Water (H2O). Stoichiometrically, CO2 + (2)H2O -> CH4 + (2)O2 The process is performed via t

Methane is CH4. Carbon from Carbon Dioxide (CO2) and Hydrogen from Water (H2O). Stoichiometrically, CO2 + (2)H2O -> CH4 + (2)O2 The process is performed via the Sabatier Reaction, which someone else linked to.