A methanol catalyst based on Cu/ZnO/Al2O3 (CZA) was prepared and mixed with four different solid acids, a pure gamma-Al2O3, a SiO2-doped gamma-Al2O3, an AlPO4-doped gamma-Al2O3 and the zeolite H-MFI 400, respectively. These admixed catalyst systems were tested in the direct synthesis of dimethyl ether from CO-rich synthesis gas (CO:H-2 = 1), which is typical for biomass-derived synthesis gas. Reactions were carried out in a laboratory plant at 250 degrees C and 51 bar for 120 h time-on-stream followed by catalyst passivation with O-2 and regeneration by hydrogenation. After catalyst regeneration, the reaction was run again for another 72 h. The catalyst system containing the zeolite exhibited highest CO-conversion. However, all catalysts showed a drop of activity after the passivation- and regeneration-process and the system with the SiO2-doped gamma-Al2O3 showed the lowest Idss of activity. Investigation of the catalysts after reaction by N2O-pulse chemisorption and XRD revealed that agglomeration of catalyst species took place leading to an increased Cu-0-particle size for all systems. This phenomenon was less pronounced in the case of the system containing the SiO2-doped gamma-Al2O3. Thus, the main cause of catalyst deactivation was found to be sintering of the catalytically active components. (C) 2016 Elsevier B.V. All rights reserved.