Conversion of Synthesis Gas to Dimethylether Over Gold-based Catalysts

It is shown that Au–zinc oxide–alumina catalysts are suitable for the water–gas shift reaction and for methanol (MeOH) and DME synthesis, indicating their use in a direct single-stage process for converting syngas to a DME + methanol mixture. Temperatures above 340 °C were required in order to obtain reasonable catalytic activity. A 67 % DME selectivity was achieved at 380 °C with a low space velocity 0.75 dm3 h−1 g−1 and 50 bar. The lower CO conversions at the higher temperature of 460 °C was probably due to the MeOH equilibrium limitation in the range of temperatures 340 to 460 °C, but deactivation is observed as well, above 460 °C. Au/ZnO/γ-Al2O3 is more stable than traditional copper-based catalysts, which are stable below about 300 °C, and then only in the absence of water. The gold composite catalyst was mainly selective toward DME, MeOH and CH4, and to C2 to C5 hydrocarbons. An analysis of the main reactions involved indicates that only the methanol synthesis reaction reaches a near-equilibrium situation, with the other reactions being under kinetic control.