Direct conversion of syngas to DME: synthesis of new Cu-based hybrid catalysts using Fehling’s solution, elimination of the calcination step

Abstract

A facile new method for the synthesis of nanostructured Cu₂O–ZnO and Cu₂O–ZnO–MgO catalysts has been described. The catalysts were physically admixed with γ-Al₂O₃ to form hybrid catalysts suitable for direct selective conversion of syngas to DME. The methanol synthesis component was synthesized from the corresponding nitrate precursors using Fehling’s solution coupled with the glucose oxidation assisted precipitation method. This method resulted in the formation of the oxide form of the catalyst from the precursor phase and avoided ex situ calcination. In the present study, along with Cu₂O, direct synthesis of divalent oxides (viz. ZnO and MgO) from their nitrate salts using Fehling’s route has been demonstrated, which has resulted in highly structured Cu₂O/ZnO/MgO catalysts. The resulting catalysts were characterized by XPS, XRD, BET-surface area, ammonia-TPD, H₂-TPR and SEM techniques. It was found that oxide phases were present in the catalyst. In addition, a different precursor phase with high purity and crystallinity along with high surface area, optimum acidity and lower reduction temperature was obtained through Fehling’s method of catalyst synthesis. Catalytic activity for syngas conversion to DME was tested in the temperature range of 200–280 °C and the pressure range of 30–50 bar. The catalyst obtained through this method exhibited a syngas conversion of 50% and a DME selectivity of 80%. The catalyst is also found to be resistant towards coke formation as compared to the catalyst with a similar composition made through the conventional co-precipitation route.