Coprecipitated Fe/K/spinel nanocomposites for Fischer-Tropsch to lower olefins

Literature about ZnAl2O4-supported iron Fischer-Tropsch to lower olefins (FTO) catalytic materials is sparse. Fe/K/spinel nanocomposites were synthesized by coprecipitation of Fe/Zn/Al nitrates with a precipitant as well as subsequent calcinations at 350 °C, followed by impregnation of potassium source. Materials were investigated by XRD, N2 sorption, FESEM, CO2-TPD as well as catalytic performance tests. Addition of potassium may remove the high-temperature desorption peak for strong basicity sites and increase both the strength and number of weak basicity sites on the surface of nanocomposites. Effects of reaction temperature, total pressure, space velocity as well as potassium content on catalytic performance of nanocomposites were systematically investigated. The ZnAl2O4 phase in support is able to remain a stable structure during the CO hydrogenation tests. The ZnAl2O4 phase may efficiently drive formed hydrocarbon molecules away from nanocomposite surface and thus can effectively hinder C–C coupling. Fe/K2O/ZnAl2O4·Al2O3 nanocomposites achieve very high short chain (C1-C4) hydrocarbon distribution value of 81.7–96.3% throughout their tested parameter range. At a condition of 0.5 MPa, 350 °C, and 1500 mL·g cat−1·h−1, the nanocomposite catalyst with a K2O content of 2%, which has a primary particle size of ca. 10 nm, achieves its maximum C2=-C4= hydrocarbon distribution of 53.4%, and, reaches a C2-C4 hydrocarbon distribution value of 61.7% which exceeds the ASF (Anderson-Schulz-Flory) limit value of 58%. These results indicate that novel supports and appropriate promoters own significant potential and are worthy of further investigations for iron-based FTO nanocomposite catalysts.