Process to prepare a hydrogen rich gas mixture from a halogen containing gas mixture comprising hydrogen and at least 50 vol. % carbon monoxide, on a dry basis, by contacting the halogen containing gas mixture with water having a temperature of between 150 and 250° C. to obtain a gas mixture poor in halogen and having a steam to carbon monoxide molar ratio of between 0.2:1 and 0.9:1 and subjecting said gas mixture poor in halogen to a water gas shift reaction wherein part or all of the carbon monoxide is converted with the steam to hydrogen and carbon dioxide in the presence of a catalyst as present in one fixed bed reactor or in a series of more than one fixed bed reactors and wherein the temperature of the gas mixture as it enters the reactor or reactors is between 190 and 230° C.