Direct conversion of syngas to dimethyl ether as a green fuel over ultrasound-assisted synthesized CuO–ZnO–Al2O3/HZSM-5 nanocatalyst: effect of active phase ratio on physicochemical and catalytic properties at different process conditions
Abstract
The effect of active phase (CZA: CuO–ZnO–Al2O3) to support (HZSM-5) ratio on the physicochemical and catalytic properties of CuO–ZnO–Al2O3/HZSM-5 nanocatalyst for direct conversion of syngas to DME (STD) has been investigated. Nanocatalysts were synthesized using a hybrid co-precipitation–ultrasound method in three ratios of CZA/HZSM-5 = 2, 3 and 4. The surface functional groups, phase evolution, morphology, reducibility and surface area of calcined nanocatalyst were investigated using FTIR, XRD, FESEM, PSD, EDX, H2-TPR and BET techniques. It was found that with varying of the CZA content, the physicochemical properties of prepared nanocatalysts changed obviously. The analysis showed that applying ultrasound energy led to uniform coating of the HZSM-5 surface by CuO–ZnO–Al2O3. Moreover, it was found that each catalyst consisted of many small particles whose shapes are almost spherical. H2-TPR profiles indicated that reducibility of nanocatalysts was increased with enhancement of CZA ratio. The effect of CZA/HZSM-5 ratio on the catalytic performance was investigated at 200–300 °C, 10–40 bar, GHSV = 600 to 1500 cm3 g h−1 and H2/CO = 2. The results showed that the CZA content has great influence on the activity of nanocatalysts and the sample with CZA/HZSM-5 = 4 showed highest catalytic activity. Furthermore, it was observed that the optimum operating condition for STD reaction is 275 °C and 40 bar. The durability of the nanocatalyst was investigated during syngas to DME conversion. The nanocatalyst loses negligible activity over the course of the reaction.