Effect of precipitants during the preparation of Cu-ZnO-Al2O3/Zr-ferrierite catalyst on the DME synthesis from syngas

The synthesis of dimethyl ether (DME) from biomass-derived model synthesis gas has been investigated on Cu-ZnO-Al₂O₃/Zr-ferrierite bifunctional catalysts. The catalysts are prepared by co-precipitation–impregnation method using Na₂CO₃, K₂CO₃ and (NH₄)₂CO₃ as the precipitants. The catalytic activity tests reveal that the best yield of DME can be obtained on the catalyst precipitated by using (NH₄)₂CO₃. Detailed characterization studies conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH₃-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and copper surface area and particle size measurements by N₂O titration method. Increasing the number of moderate acidic sites and facilitation of easily reducible copper species with small particle size are found to be the prime reasons for the superior functionality of the (NH₄)₂CO₃ precipitated catalyst. The usage of (NH₄)₂CO₃ also leaves no residual ions, whereas the presence of residual K⁺ and Na⁺ ions in the case of K₂CO₃ and Na₂CO₃ precipitated catalysts leads to lower activity and selectivity.