Deactivation of methanol synthesis catalysts - a review

The current knowledge of the deactivation phenomenon of the low-temperature gasphase methanol synthesis catalyst is reviewed. Under normal operating conditions, the catalyst Cu-Zn oxide has a rather long lifetime of a few years. However, the catalyst is very sensitive to sulfur poisoning, and the sulfur content in the feed stream needs to be reduced to less than 0.5 ppm. The ZnO component in the catalyst is a scavenger for sulfur by reacting with it to form Zn sulfide and sulfate, which helps extend the catalyst life. The catalyst can also be deactivated thermally, especially at above 300°C because of the growth of the Cu crystallites and the resulting loss of catalytically active area. Deposition of Fe or Ni results in loss of activity by site blocking as well as production of hydrocarbon products as a competitive reaction, whereas Cl facilitates sintering of Cu. The catalyst for the liquid-phase synthesis is also susceptible to the same types of deactivation. Catalysts derived from Cu-rare earth alloys are very susceptible to deactivation by CO₂, O₂, and to a lesser extent, H₂O.