The influence of impurities in steel mill exhaust gases on ternary Cu/ZnO/Al(2)O(3)catalysts was studied for conventional methanol synthesis, which is one of the central reactions within the cross-industrial approach of Carbon2Chem (R). A series of hydrocarbons was identified as inert spectators for methanol synthesis. Several catalyst poisons like N-containing compounds or O(2)show reversible characteristics at low pressure. However, by increasing the partial pressure of O-2, poisoning becomes irreversible, indicating different poisoning mechanisms concerning the reversibility of deactivation.