The effect of Co-feeding ethene on Fischer Tropsch Synthesis to Olefins over Co-based catalysts

Abstract Understanding the secondary reactions of olefins in Fischer Tropsch Synthesis (FTS) is crucial for enhancing olefin selectivity in Fischer Tropsch to Olefin (FTO) reaction. Equimolar ethene towards CO was used as a probe to be cofed into the syngas (H2: CO = 2) to study the effect on the product distribution over cobalt-based catalysts supported on γ-alumina, α-alumina and carbon nanotube (CNT), respectively. The experiments were performed at T = 210 °C; Ptot = 1.85 bar, PCO = 0.11 bar; PH2 = 0.22 bar; PC2H4 = 0 or 0.11 bar with Ar as the balance. On all three catalysts, ethene co-feeding at this concentration inhibited CO conversion and the products were mainly from ethene. The products showed similar Anderson-Schulz-Flory (ASF) distribution as typical for FTS products. Ethene co-feeding can both enhance the chain growth probability and significantly increase the O/P ratio of C3-C6 hydrocarbons. An isotopic switch from 12CO/H2 /Ar→13CO/H2/C2H4/Kr proved that ethene can hydrocrack to C1 intermediates and be incorporated into the growing chain. On the other hand, the hydrogenation activity can be significantly suppressed due to the H2 scavenging effect and possibly competitive adsorption with H2.