Direct conversion of syngas to DME over CuO-ZnO-Al2O3/HZSM-5 nanocatalyst synthesized via ultrasound-assisted co-precipitation method: New insights into the role of gas injection

In this study, direct synthesis of dimethyl ether (DME) is conducted over a bifunctional CuO–ZnO–Al2O3/H Zeolite Socony Mobil-5 (HZSM-5) nanocatalyst. A hybrid method of ultrasound-assisted co-precipitation is used for the synthesis of catalysts, and the effect of gas injection during sonication is investigated. The physicochemical characteristics of the catalysts are analysed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), particle size distribution (PSD), energy dispersive X-ray (EDX), Brunauer–Emmett–Teller (BET) and Fourier-transformed infrared (FTIR) methods. In the absence of gas injection, the acetate-based catalysts have a better morphology and higher surface area than the nitrate-based catalyst. Gas injection significantly changes the morphology and structural properties of the acetate-based catalyst. High surface area, narrow PSD and better dispersion of small CuO crystals are obtained in a gas-injected synthesized sample. DME synthesis experiments showed that the CO conversion and DME selectivity are correlated with surface area, nanocatalyst particle size and its dispersion. The gas-injected CuO–ZnO–Al2O3/HZSM-5 nanocatalyst that has the highest surface area and the smallest dispersed particles showed more than 70% DME selectivity. The gas-injected CuO–ZnO–Al2O3/HZSM-5 nanocatalyst exhibited high stability in terms of CO conversion and DME yield over 1440-min time on a stream test at 275°C, 40 bar and 18 000 cm3 g.h−1. Copyright © 2014 John Wiley & Sons, Ltd.