Valorization of steel-work off-gases: Influence of impurities on the performance of Cu-based methanol synthesis catalyst

The use of steel-work off-gases as CO2 source for methanol production is a promising strategy for the decarbonization of the steel industry. In this work, we show that typical impurities, namely S, N, Na, Ca and Fe, reduce the activity of a commercial CuO/ZnO/Al2O3 catalyst by blocking part of the Cu active sites. The extent of the activity loss is proportional to the poison-induced decrease in the exposed Cu surface area, suggesting that the poisons do not modify the nature, but rather the number of active sites. The only deviation is observed for Na, as its strong basicity leads to stronger binding of CO2 on the catalyst surface. Moreover, all catalysts suffer from methanol selectivity losses with time, due to thermal sintering that occurs similarly over the untreated and poisoned samples. Industrial CO2 off-gases can thus be exploited for methanol production after appropriate purification targeted primarily at the removal of metal impurities. The presence of sulfur and nitrogen is less critical to the catalyst performance.