Direct conversion of syngas to dimethyl ether as a green fuel over CuO-ZnO-Al2O3/HZSM-5 nanocatalyst: Effect of aging time on physicochemical and catalytic properties

Abstract

The effect of aging time on physicochemical and catalytic properties of CuO-ZnO-Al2O3/HZSM-5 nanocatalyst for direct conversion of syngas to dimethyl ether (DME) has been investigated. Nanocatalysts were synthesized using co-precipitation method in which the aging time varied from 0 to 6 h. The physicochemical properties of the nanocatalysts were studied by X-ray diffraction, Brunauer, Emmett, and Teller, Field Emission Scanning Electron Microscopy (FESEM), energy dispersive X-ray, transmission electron microscopy, FTIR, and temperature-programmed reduction by hydrogen (TPR-H2) techniques. Results showed that the crystallinity of CuO-ZnO-Al2O3 has been increased significantly by increasing of aging time. FESEM analysis showed that, with extension of the aging time, the aggregation of CuO-ZnO-Al2O3 over HZSM-5 has been increased. The size of the particles in the active phase was between 25.0 and 127.1 nm with an average size of 48.36 nm. TPR-H2 profiles indicated that reducibility of nanocatalysts was enhanced with increasing of aging time. Catalytic performance was investigated at 200–300 °C, 10–40 bar, GHSV = 600 cm3 g/h, and H2/CO = 2. It was found that the increase of aging time had a great influence on the activity of nanocatalysts. Moreover, the 6 h aged nanocatalyst displayed the highest catalytic activity. It was also observed that the optimum operating conditions for syngas to DME reaction were 275 °C and 40 bar.