Titania-supported bimetallic catalysts combined with HZSM-5 for Fischer-Tropsch synthesis

Fischer-Tropsch synthesis was studied in a fixed-bed reactor over single-metal and bimetallic alloy catalysts, selected from Co, Ni, and Fe, supported on TiO2 at a total metal loading of 10 wt %. The catalysts, prepared by incipient wetness impregnation using nitrate precursors, were tested as is and in combination with a HZSM-5 zeolite. The test conditions were 1 MPa, 250 degrees C, H-2/CO = 1, and weight hourly space velocity (WHSV) = 0.77 h(-1). Alloying of metals resulted in a significant enhancement in CO conversion without an increase in methane selectivity. A 50:50 weight ratio Co-Ni catalyst physically mixed with HZSM-5 (5% Co-5% Ni/TiO2 + HZSM-5) gave the highest CO conversion (45.2%) at the conditions tested. This compares to conversion of 8.95% and 10.5% with Co-only and Ni-only catalysts, respectively. Mixing the Co-Ni catalyst with HZSM-5 resulted in a significant reduction in methane selectivity and a significant increase in C-4(+) selectivity. The aromatic fraction increased from 1.5 to 8.1 wt %, the C-2(+) olefins were nearly eliminated, and i-C4H10 increased from 2.3 to 58.5 wt % in the C-4 fraction.