synthesis catalyst and a ZSM-5 methanol dehydration catalyst was used. The metallic catalyst appears to deactivate due to Cu sintering, with no apparent effect from the methanol dehydration step under the conditions applied. The acid catalyst deactivates due to accumulation of hydrocarbon species formed in its pores. Synthesis gas composition, i.e., H-2/CO ratio and CO2-content (which directly affects partial pressure of water), seems to influence the zeolite deactivation. Catalysts for direct synthesis of dimethyl ether (DME) from synthesis gas should essentially contain two functions, i.e., methanol synthesis and methanol dehydration. In the present work, the deactivation of both functions of hybrid catalysts during direct DME synthesis under industrially relevant conditions has been investigated with special focus on the influence of each reaction step on the deactivation of the catalyst function corresponding to the other step. A physical mixture of a Cu-Zn-based methanol