Enhanced conversion of syngas to high-quality diesel fuel over ZrO2 and acidized carbon nanotube bifunctional catalyst

Direct syngas conversion for diesel fuel becomes an attractive route for its possibility of utilizing non-petroleum carbon resources. However, there is a limited selectivity of around 36% for diesel hydrocarbons (C9-C22) via the conventional Fischer-Tropsch process due to the Anderson-Schulz-Flory (ASF) constraint. Herein, bifunctional catalysts composed of zirconium dioxide (ZrO2) dispersed on multi-walled carbon nanotubes (CNT) (ZrO2/CNT) were successfully designed and applied for direct conversion of syngas into diesel with selectivity far beyond the ASF limitation. At 350 °C with the pressure of 3 MPa, H2/CO of 2 and gas hourly space velocity of 2400 mL·h−1·gcat−1, ZrO2/CNT gave an unexceptionable C9-C22 selectivity of 50.74% at a single pass CO conversion of 43.86% compared with those (9.11% and 20.55%, respectively) of ZnO/CNT and those (14.07% and 25.76%, respectively) of ZnO-ZrO2/CNT. The iso/n-paraffin ratio in the C9-C22 reached up to 16. Moreover, after 100 h of operation, the catalyst still showed remarkable catalytic activity with CO conversion remaining at 40.61%, diesel hydrocarbon selectivity, and methane selectivity at 42.27% and 7.67%, respectively, while the by-product CO2 selectivity was also stable at about 3.77%.