The effect of co-feeding ethene on Fischer-Tropsch synthesis to olefins over Co-based catalysts

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 (H-2: CO = 2) to study the effect on the product distribution over cobalt-based catalysts supported on gamma-alumina, alpha-alumina and carbon nanotube (CNT), respectively. The experiments were performed at T = 210 degrees C; P-tot = 1.85 bar, P-CO = 0.11 bar; P-H2 = 0.22 bar; P-C2H4 = 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 C-3-C-6 hydrocarbons. An isotopic switch from (CO)-C-12/H-2 /Ar ->(CO)-C-13/H-2/C2H4/Kr proved that ethene can hydrocrack to C-1 intermediates and be incorporated into the growing chain. On the other hand, the hydrogenation activity can be significantly suppressed due to the H-2 scavenging effect and possibly competitive adsorption with H-2.