The effects of preparation methods and dehydration components on catal
ytic properties and the structures of bifunctional catalysts were inve
stigated. Catalytic synthesis of dimethyl ether from synthesis gas was
evaluated in a fixed-bed flow microreactor at a pressure of 4.0 MPa a
nd a GHSV of 1500 h(-1). Characterization of catalysts has been carrie
d out using XRD, TPR, Pyridine-TPD, CO2-TPD and XPS. The experimental
results show that CuO-ZnO-Al2O3/HZSM-5 and CuO-ZnO-Al2O3/HSY catalysts
, which were prepared by a coprecipitating sedimentation method, exhib
it the highest catalytic activity for direct synthesis of dimethyl eth
er from synthesis gas with 89% CO conversion and 99% selectivity of di
methyl ether (in organic products). In addition, the results indicate
that the dehydration step of the reaction occurs on the weak acidic si
tes and there is a 'synergistic effect' between the two kinds of activ
e components in bifunctional catalysts. (C) 1998 Elsevier Science B.V.