Conversion of Synthesis Gas to Dimethylether Over Gold-based Catalysts

Abstract

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.